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The conventional gradient‐echo steady‐state signal model is the basis of various spoiled gradient‐echo (SPGR) based quantitative MRI models, including variable flip angle (VFA) MRI and dynamic contrast‐enhanced MRI (DCE). However, including preparation pulses, such as fat suppression or saturation bands, disrupts the steady‐state and leads to a bias in T1 and DCE parameter estimates. This work introduces a signal model that improves the accuracy of VFA T1‐mapping and DCE for interrupted spoiled gradient‐echo (I‐SPGR) acquisitions. The proposed model was applied to a VFA T1‐mapping I‐SPGR sequence in the Gold Standard T1‐phantom (3 T), in the brain of four healthy volunteers (3 T), and to an abdominal DCE examination (1.5 T). T1‐values obtained with the proposed and conventional model were compared to reference T1‐values. Bland–Altman analysis (phantom) and analysis of variance (in vivo) were used to test whether bias from both methods was significantly different (p = 0.05). The proposed model outperformed the conventional model by decreasing the bias in the phantom with respect to the phantom reference values (mean bias ‐2 vs. ‐35% at 3 T) and in vivo with respect to the conventional SPGR (‐6 vs. ‐37% bias in T1, p < 0.01). The proposed signal model estimated approximately 48% (depending on baseline T1) higher contrast concentrations in vivo, which resulted in decreased DCE pharmacokinetic parameter estimates of up to 35%. The proposed signal model improves the accuracy of quantitative parameter estimation from disrupted steady‐state I‐SPGR sequences. It therefore provides a flexible method for applying fat suppression, saturation bands, and other preparation pulses in VFA T1‐mapping and DCE. [ABSTRACT FROM AUTHOR]

Purpose: Breath‐held fat‐suppressed volumetric T1‐weighted MRI is an important and widely‐used technique for evaluating the abdomen. Both fat‐saturation and Dixon‐based fat‐suppression methods are used at conventional field strengths; however, both have challenges at lower field strengths (<1.5T) due to insufficient fat suppression and/or inadequate resolution. Specifically, at lower field strengths, fat saturation often fails due to the short T1 of lipid; and Cartesian Dixon imaging provides poor spatial resolution due to the need for a long ΔTE, due to the smaller Δf between water and lipid. The purpose of this work is to demonstrate a new approach capable of simultaneously achieving excellent fat suppression and high spatial resolution on a 0.55T whole‐body system. Methods: We applied 3D stack‐of‐spirals Dixon imaging at 0.55T, with compensation of concomitant field phase during reconstruction. The spiral readouts make efficient use of the requisite ΔTE. We compared this with 3D Cartesian Dixon imaging. Experiments were performed in 2 healthy and 10 elevated liver fat volunteers. Results: Stack‐of‐spirals Dixon imaging at 0.55T makes excellent use of the required ΔTE, provided high SNR efficiency and finer spatial resolution (1.7 × 1.7 × 5 mm3) compared Cartesian Dixon (3.5 × 3.5 × 5 mm3), within a 17‐s breath‐hold. We observed successful fat suppression, and improved definition of structures such as the liver, kidneys, and bowel. Conclusion: We demonstrate that high‐resolution single breath‐hold volumetric abdominal T1‐weighted imaging is feasible at 0.55T using spiral sampling and concomitant field correction. This is an attractive alternative to existing Cartesian‐based methods, as it simultaneously provides high‐resolution and excellent fat‐suppression. [ABSTRACT FROM AUTHOR]

Purpose: To introduce an alternative idea for fat suppression that is suited both for low‐field applications where conventional fat‐suppression approaches become ineffective due to narrow spectral separation and for applications with strong B0 homogeneities. Methods: Separation of fat and water is achieved by sweeping the frequency of RF saturation pulses during continuous radial acquisition and calculating frequency‐resolved images using regularized iterative reconstruction. Voxel‐wise signal‐response curves are extracted that reflect tissue's response to RF saturation at different frequencies and allow the classification into fat or water. This information is then utilized to generate water‐only composite images. The principle is demonstrated in free‐breathing abdominal and neck examinations using stack‐of‐stars 3D balanced SSFP (bSSFP) and gradient‐recalled echo (GRE) sequences at 0.55 and 3T. Moreover, a potential extension toward quantitative fat/water separation is described. Results: Experiments with a proton density fat fraction (PDFF) phantom validated the reliability of fat/water separation using signal‐response curves. As demonstrated for abdominal imaging at 0.55T, the approach resulted in more uniform fat suppression without loss of water signal and in improved CSF‐to‐fat signal ratio. Moreover, the approach provided consistent fat suppression in 3T neck exams where conventional spectrally‐selective fat saturation failed due to strong local B0 inhomogeneities. The feasibility of simultaneous fat/water quantification has been demonstrated in a PDFF phantom. Conclusion: The proposed principle achieves reliable fat suppression in low‐field applications and adapts to high‐field applications with strong B0 inhomogeneity. Moreover, the principle potentially provides a basis for developing an alternative approach for PDFF quantification. [ABSTRACT FROM AUTHOR]

Objectives: To find the optimal acceleration factor (AF) of the compressed SENSE (CS) technique for uterine isotropic high-resolution 3D T2-weighted imaging (3D-ISO-T2WI). Methods: A total of 91 female volunteers from the First Affiliated Hospital of Dalian Medical University, Chu Hsien-I Memorial Hospital and Tianjin Institute of Endocrinology, and The Fourth Hospital of Harbin were recruited. A total of 44 volunteers received uterus sagittal 3D-ISO-T2WI scans on 3.0T MRI device with different CS AFs (including SENSE3, CS3, CS4, CS5, CS6, and CS7), 51 received 3D-ISO-T2WI scans with different degrees of fat suppression (none, light, moderate, and severe), while 4 volunteers received both series of scans. Image quality was subjectively evaluated with a 3-point scoring system. Junction zone signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and myometrial SNR were also calculated. Intraclass correlation coefficients were used to analyse the consistency of the measurement results by 2 observers. Analysis of variance test or Friedman rank sum test was used to compare the differences in subjective scores, SNR, and CNR under different AFs/different degrees of fat suppression. Results: Images by AFs of CS3, CS4, and CS5 had the highest SNR and CNR. Among them, CS5 had the shortest scan time. CS5 also had one of the highest subjective scores. There was no significant difference in SNR and CNR among images acquired with different degrees of fat suppression. Also, images with moderate fat suppression had the highest subjective scores. Conclusion: The CS5 combined with moderate fat suppression is recommended for routine female pelvic 3D-ISO-T2WI scan. Advances in knowledge: The CS5 has the highest image quality and has the shortest scan time, which is the best AF. Moderate fat suppression has the highest subjective scores. The CS5 and moderate fat suppression are the best combination for a female pelvic 3D-ISO-T2WI scan. [ABSTRACT FROM AUTHOR]

For patients with complete breast resection, conventional contrast-enhanced T1-weighted imaging (CE-T1WI) with frequency-selective spectral attenuated inversion recovery (SPAIR) provides limited fat suppression on the postoperative side due to the uneven skin surface, inhomogeneous tissue environment, and frequency-selective feature of the SPAIR scheme, leading to difficulties in precise diagnosis. This study aimed to investigate the image quality and performance of the Dixon method compared with SPAIR in breast high-resolution CE-T1WI for mastectomy patients. Sixty female patients who had not performed any breast surgeries were randomly selected retrospectively as the control group. Postmastectomy female patients were enrolled to undergone high-resolution CE-T1WI with SPAIR and Dixon breast scans. Subjective scores were rated using a 5-point scale. Objective parameters, including contrast-to-noise ratio (CNR), edge sharpness, and signal uniformity were measured and calculated. The Wilcoxon rank-sum test and Kappa statistic were used. A total of 114 consecutive postmastectomy patients were included. Subjective scores of T1WI-SPAIR in the control group were all significantly better than those with SPAIR on the postoperative side of mastectomy patients (P < 0.01). Dixon outperformed SPAIR with significantly better subjective scores in regards to uniformity and degree of fat-suppression, anatomical structures depiction, lesion conspicuity, and axillary visibility (p < 0.05) in both post- and non-operative sides and bilateral axillary areas through the paired comparison. The objective parameters of Dixon were significantly better than those of SPAIR. The Dixon method provided better image uniformity and higher fat suppression efficiency, and showed significant advantages in delineating the anatomical structures, with better axillary and lesion visibilities, especially on the completely removed breast side. [ABSTRACT FROM AUTHOR]

PurposeFatty acid composition of the orbit makes it challenging to achieve complete fat suppression during orbit MR imaging. Implementation of a fat suppression technique capable of suppressing signals from saturated (aliphatic) and unsaturated (olefinic or protons at double-bonded carbon sites) fat would improve the visualization of an optical nerve. Furthermore, the ability to semi-quantify the fractions of aliphatic and olefinic fat may potentially provide valuable information in assessing orbit pathology.MethodsA phantom study was conducted on various oil samples on a clinical 3 Tesla scanner. The imaging protocol included three 2D fast spin echo (FSE) sequences: in-phase, polarity-altered spectral and spatial selective acquisition (PASTA), and a combination of PASTA with opposed phase in olefinic and aliphatic chemical shift. The results were validated against high-resolution 11.7T NMR and compared with images acquired with spectral attenuated inversion recovery (SPAIR) and chemical shift selective (CHESS) fat suppression techniques. In-vivo data were acquired on eight healthy subjects and were compared with the prior histological studies.ResultsPASTA with opposed phase achieved complete suppression of fat signals in the orbits and provided images of well-delineated optical nerves and muscles in all subjects. The olefinic fat fraction in the olive, walnut, and fish oil phantoms at 3T was found to be 5.0%, 11.2%, and 12.8%, respectively, whereas 11.7T NMR provides the following olefinic fat fractions: 6.0% for olive, 11.5% for walnut, and 12.6% for fish oils. For the in-vivo study, on average, olefinic fat accounted for 9.9% ± 3.8% of total fat while the aliphatic fat fraction was 90.1% ± 3.8%, in the normal orbits.ConclusionWe have introduced a new fat suppression technique using PASTA with opposed phase and applied it to human orbits. The purposed method achieves an excellent orbital fat suppression and the quantification of aliphatic and olefinic fat signals.

Introduction: Multiple Myeloma (MM) represents a malignant proliferation of plasma cells derived from a single clone. Imaging of the skeleton beyond symptomatic areas is useful for myeloma staging and subsequent follow-up for treatment response and disease relapse. Despite research comparing the Dixon sequence to conventional sequences in a variety of musculoskeletal disorders, there is a lack of studies regarding the Dixon sequence’s application in MM. Aim: To compare the contrast of MM focal lesions in all four T2-weighted Dixon and Conventional T1-weighted spin-echo and Short Tau Inversion Recovery (STIR) images. Materials and Methods: This cross-sectional study was conducted in the Department of Radiology at Kovai Medical Centre and Hospitals (KMCH), Coimbatore, Tamil Nadu, India. All newly diagnosed and known cases of MM, either biopsy-proven or strongly suspected based on other diagnostic testing conforming to International Myeloma Working Group (IMWG) criteria from December 2020 to July 2022, were included in the study. A total of 43 patients with 142 focal MM lesions were included. Contrast between focal MM lesions and surrounding bone marrow was calculated on T1-weighted spin-echo, STIR, and T2-weighted Dixon (all four) images. Statistical analysis was done using repeated measures of Analysis of Variance (ANOVA) with Bonferroni correction to control the type I error on multiple comparisons to find the significant difference between multivariate analyses. A probability value of 0.05 was considered a significant level for all statistical tools. Results: The study population consisted of 21 men and 22 women with a mean age of 65.3±8.6 years {Mean±Standard Deviation (SD)}. Contrast values in all four T2 Dixon images, STIR, and T1-weighted images were as follows: T2 Dixon Fat-only (FO) images (0.86.±0.09) (SD); range: (0.46-0.99), T2-weighted Dixon Water-only (WO) images (0.54±0.14) (SD); range: (0.14-0.82), T2 Dixon In-phase (IP) images (0.20±0.13) (SD); range: (0.02-0.41), T2-weighted Dixon Out-phase (OP) images (0.53±0.19) (SD); range: (0.12-0.87), STIR images (0.47±0.12) (SD); range: (0.12-0.73), and T1 images (0.23±0.12) (SD); range: (0.01-0.55). The mean contrast was highest on T2 Dixon fat-only images (p

Introduction: Multiple Myeloma (MM) represents a malignant proliferation of plasma cells derived from a single clone. Imaging of the skeleton beyond symptomatic areas is useful for myeloma staging and subsequent follow-up for treatment response and disease relapse. Despite research comparing the Dixon sequence to conventional sequences in a variety of musculoskeletal disorders, there is a lack of studies regarding the Dixon sequence's application in MM. Aim: To compare the contrast of MM focal lesions in all four T2-weighted Dixon and Conventional T1-weighted spin-echo and Short Tau Inversion Recovery (STIR) images. Materials and Methods: This cross-sectional study was conducted in the Department of Radiology at Kovai Medical Centre and Hospitals (KMCH), Coimbatore, Tamil Nadu, India. All newly diagnosed and known cases of MM, either biopsyproven or strongly suspected based on other diagnostic testing conforming to International Myeloma Working Group (IMWG) criteria from December 2020 to July 2022, were included in the study. A total of 43 patients with 142 focal MM lesions were included. Contrast between focal MM lesions and surrounding bone marrow was calculated on T1-weighted spin-echo, STIR, and T2-weighted Dixon (all four) images. Statistical analysis was done using repeated measures of Analysis of Variance (ANOVA) with Bonferroni correction to control the type I error on multiple comparisons to find the significant difference between multivariate analyses. A probability value of 0.05 was considered a significant level for all statistical tools. Results: The study population consisted of 21 men and 22 women with a mean age of 65.3±8.6 years {Mean±Standard Deviation (SD)}. Contrast values in all four T2 Dixon images, STIR, and T1-weighted images were as follows: T2 Dixon Fat-only (FO) images (0.86.±0.09) (SD); range: (0.46-0.99), T2-weighted Dixon Water-only (WO) images (0.54±0.14) (SD); range: (0.14-0.82), T2 Dixon In-phase (IP) images (0.20±0.13) (SD); range: (0.02-0.41), T2-weighted Dixon Out-phase (OP) images (0.53±0.19) (SD); range: (0.12-0.87), STIR images (0.47±0.12) (SD); range: (0.12-0.73), and T1 images (0.23±0.12) (SD); range: (0.01-0.55). The mean contrast was highest on T2 Dixon fat-only images (p<0.0005) compared to T1 images, with the lowest contrast seen in IP images and intermediate values in OP images. Conclusion: In conclusion, fat-only images of the T2 multipoint Dixon sequence provide significant contrast compared to conventional T1-weighted imaging. Dixon water-only images provide fat suppression that is not inferior to STIR images. While Dixon techniques in the diagnosis of MM did not significantly differ from the conventional sequence, Dixon stands out from conventional sequences when considering the study duration and contrast between the lesion and normal bone marrow. [ABSTRACT FROM AUTHOR]

Free-running 5D whole-heart coronary MR angiography (MRA) is gaining in popularity because it reduces scanning complexity by removing the need for specific slice orientations, respiratory gating, or cardiac triggering. At 3T, a gradient echo (GRE) sequence is preferred in combination with contrast injection. However, neither the injection scheme of the gadolinium (Gd) contrast medium, the choice of the RF excitation angle, nor the dedicated image reconstruction parameters have been established for 3T GRE free-running 5D whole-heart coronary MRA. In this study, a Gd injection scheme, RF excitation angles of lipid-insensitive binominal off-resonance RF excitation (LIBRE) pulse for valid fat suppression and continuous data acquisition, and compressed-sensing reconstruction regularization parameters were optimized for contrast-enhanced free-running 5D whole-heart coronary MRA using a GRE sequence at 3T. Using this optimized protocol, contrast-enhanced free-running 5D whole-heart coronary MRA using a GRE sequence is feasible with good image quality at 3T. [ABSTRACT FROM AUTHOR]

Purpose: Fatty acid composition of the orbit makes it challenging to achieve complete fat suppression during orbitMR imaging. Implementation of a fat suppression technique capable of suppressing signals from saturated (aliphatic) and unsaturated (olefinic or protons at double-bonded carbon sites) fat would improve the visualization of an optical nerve. Furthermore, the ability to semi-quantify the fractions of aliphatic and olefinic fat may potentially provide valuable information in assessing orbit pathology. Methods: A phantom study was conducted on various oil samples on a clinical 3 Tesla scanner. The imaging protocol included three 2D fast spin echo (FSE) sequences: in-phase, polarity-altered spectral and spatial selective acquisition (PASTA), and a combination of PASTA with opposed phase in olefinic and aliphatic chemical shift. The results were validated against high-resolution 11.7T NMR and compared with images acquired with spectral attenuated inversion recovery (SPAIR) and chemical shift selective (CHESS) fat suppression techniques. In-vivo data were acquired on eight healthy subjects and were compared with the prior histological studies. Results: PASTA with opposed phase achieved complete suppression of fat signals in the orbits and provided images of well-delineated optical nerves and muscles in all subjects. The olefinic fat fraction in the olive, walnut, and fish oil phantoms at 3T was found to be 5.0%, 11.2%, and 12.8%, respectively, whereas 11.7T NMR provides the following olefinic fat fractions: 6.0% for olive, 11.5% for walnut, and 12.6% for fish oils. For the in-vivo study, on average, olefinic fat accounted for 9.9% ± 3.8% of total fat while the aliphatic fat fraction was 90.1% ± 3.8%, in the normal orbits. Conclusion: We have introduced a new fat suppression technique using PASTA with opposed phase and applied it to human orbits. The purposed method achieves an excellent orbital fat suppression and the quantification of aliphatic and olefinic fat signals. [ABSTRACT FROM AUTHOR]

Introduction: Magnetic resonance imaging (MRI) staging scans are critical for the diagnosis and treatment of patients with nasopharyngeal cancer (NPC). We aimed to evaluate the application value of LAVA-Flex and T1WI-IDEAL sequences in MRI staging scans. Methods: Eighty-four newly diagnosed NPC patients underwent both LAVA-Flex and T1WI-IDEAL sequences during MRI examinations. Two radiologists independently scored the acquisitions of image quality, fat suppression quality, artifacts, vascular and nerve display. The obtained scores were compared using the Wilcoxon signed rank test. According to the signal intensity (SI) measurements, the uniformity of fat suppression, contrast between tumor lesions and subcutaneous fat tissue, and signal-to-noise ratio (SNR) were compared by the paired t-test. Results: Compared to the T1WI-IDEAL sequence, LAVA-Flex exhibited fewer artifacts (P<0.05), better visualization of nerves and vessels (P<0.05), and performed superior in the fat contrast ratio of the primary lesion and metastatic lymph nodes (0.80 vs. 0.52, 0.81 vs. 0.56, separately, P<0.001). There was no statistically significant difference in overall image quality, tumor signal-to-noise ratio (SNR), muscle SNR, and the detection rate of lesions between the two sequences (P>0.05). T1WI-IDEAL was superior to LAVA-Flex in the evaluation of fat suppression uniformity (P<0.05). Discussion: LAVA-Flex sequence provides satisfactory image quality and better visualization of nerves and vessels for NPC with shorter scanning times. [ABSTRACT FROM AUTHOR]

Peripheral neuropathy is known to be one of the most common neurological disorders. Despite the great diagnostic value of electroneuromyography and ultrasound, addressing the diagnostics and differential diagnostics of peripheral nerve diseases of different origin could be challenging. In recent years, magnetic resonance tomography has been increasingly used for evaluating cases of suspected or established peripheral neuropathy with excellent results. This manuscript mainly deals with the advantages and limitations of the aforementioned diagnostic instruments, technical considerations according to different anatomy of peripheral nerves, along with state-of-the-art technical decisions, frequently used magnetic resonance imaging sequences and their diagnostic value based on own observation, and recommendations for contrast enhancement use and different methods of fat suppression. Currently, there is practically no standardized description of normal magnetic resonance imaging features of peripheral nerves, as well as their changes in different diseases. The evaluation of images is mainly based on the radiologist experience, which obviously decreases method’s diagnostic value. Studies of large numbers involving healthy volunteers and patients with peripheral neuropathies of different origin are required to address this issue.

IntroductionMagnetic resonance imaging (MRI) staging scans are critical for the diagnosis and treatment of patients with nasopharyngeal cancer (NPC). We aimed to evaluate the application value of LAVA-Flex and T1WI-IDEAL sequences in MRI staging scans.MethodsEighty-four newly diagnosed NPC patients underwent both LAVA-Flex and T1WI-IDEAL sequences during MRI examinations. Two radiologists independently scored the acquisitions of image quality, fat suppression quality, artifacts, vascular and nerve display. The obtained scores were compared using the Wilcoxon signed rank test. According to the signal intensity (SI) measurements, the uniformity of fat suppression, contrast between tumor lesions and subcutaneous fat tissue, and signal-to-noise ratio (SNR) were compared by the paired t-test.ResultsCompared to the T1WI-IDEAL sequence, LAVA-Flex exhibited fewer artifacts (P0.05). T1WI-IDEAL was superior to LAVA-Flex in the evaluation of fat suppression uniformity (P

In breast MRI with diffusion-weighted imaging (DWI), fat suppression is essential for eliminating the dominant lipid signal. This investigation evaluates a combined water-excitation-spectral-fatsat method (WEXfs) versus standard spectral attenuated inversion recovery (SPAIR) in high-resolution 3-Tesla breast MRI. Multiparametric breast MRI with 2 echo-planar DWI sequences was performed in 83 patients (50.1 ± 12.6 years) employing either WEXfs or SPAIR for fat signal suppression. Three radiologists assessed overall DWI quality and delineability of 88 focal lesions (28 malignant, 60 benign) on images with b values of 800 and 1600 s/mm2, as well as apparent diffusion coefficient (ADC) maps. For each fat suppression method and b value, the longest lesion diameter was determined in addition to measuring the signal intensity in DWI and ADC value in standardized regions of interest. Regardless of b values, image quality (all p < 0.001) and lesion delineability (all p ≤ 0.003) with WEXfs-DWI were deemed superior compared to SPAIR-DWI in benign and malignant lesions. Irrespective of lesion characterization, WEXfs-DWI provided superior signal-to-noise, contrast-to-noise and signal-intensity ratios with 1600 s/mm2 (all p ≤ 0.05). The lesion size difference between contrast-enhanced T1 subtraction images and DWI was smaller for WEXfs compared to SPAIR fat suppression (all p ≤ 0.007). The mean ADC value in malignant lesions was lower for WEXfs-DWI (p < 0.001), while no significant ADC difference was ascertained between both techniques in benign lesions (p = 0.947). WEXfs-DWI provides better subjective and objective image quality than standard SPAIR-DWI, resulting in a more accurate estimation of benign and malignant lesion size. [ABSTRACT FROM AUTHOR]

PurposeTo design a soft-hard composite pulse for fat suppression and water excitation in ultrashort echo time (UTE) imaging with minimal short T2 signal attenuation.MethodsThe composite pulse contains a narrow bandwidth soft pulse centered on the fat peak with a small negative flip angle (-α) and a short rectangular pulse with a small positive flip angle (α). The fat magnetization experiences both tipping-down and -back with an identical flip angle and thus returns to the equilibrium state, leaving only the excited water magnetization. Bloch simulations, as well as knee, tibia, and ankle UTE imaging studies, were performed to investigate the effectiveness of fat suppression and corresponding water signal attenuation. A conventional fat saturation (FatSat) module was used for comparison. Signal suppression ratio (SSR), defined as the ratio of signal difference between non-fat-suppression and fat-suppression images over the non-fat-suppression signal, was introduced to evaluate the efficiency of the composite pulse.ResultsNumerical simulations demonstrate that the soft-hard pulse has little saturation effect on short T2 water signals. Knee, tibia, and ankle UTE imaging results suggest that comparable fat suppression can be achieved with the soft-hard pulse and the FatSat module. However, much less water saturation is induced by the soft-hard pulse, especially for short T2 tissues, with SSRs reduced from 71.8 ± 6.9% to 5.8 ± 4.4% for meniscus, from 68.7 ± 5.5% to 7.7 ± 7.6% for bone, and from 62.9 ± 12.0% to 4.8 ± 3.2% for the Achilles tendon.ConclusionThe soft-hard composite pulse can suppress fat signals in UTE imaging with little signal attenuation on short T2 tissues.

PurposeIn ultrashort echo time (UTE) imaging, fat suppression can improve short T2 * contrast but can also reduce short T2 * signals. The conventional two-point Dixon (2p-Dixon) method does not perform well due to short T2 * decay. In this study, we propose a new method to suppress fat for high contrast UTE imaging of short T2 tissues, utilizing a single-point Dixon (1p-Dixon) method.MethodsThe proposed method utilizes dual-echo UTE imaging, where UTE is followed by the second TE, chosen flexibly. Fat is estimated by applying a 1p-Dixon method to the non-UTE image after correction of phase errors, which is used to suppress fat in the UTE image. In vivo ankle and knee imaging were performed at 3 T to evaluate the proposed method.ResultIt was observed that fat and water signals in tendons were misestimated by the 2p-Dixon method due to signal decay, while the 1p-Dixon method showed reliable fat and water separation not affected by the short T2 * signal decay. Compared with the conventional chemical shift based fat saturation technique, the 1p-Dixon based approach showed much stronger signal intensities in the Achilles, quadriceps, and patellar tendons, with significantly improved contrast to noise ratios (CNRs) of 11.8 ± 2.2, 16.0 ± 1.6, and 26.8 ± 1.3 with the 1p-Dixon method and 0.6 ± 0.2, 4.6 ± 1.0, and 17.5 ± 1.4 with regular fat saturation, respectively.ConclusionThe proposed 1p-Dixon based fat suppression allows more flexible selection of imaging parameters and more accurate fat and water separation over the conventional 2p-Dixon in UTE imaging. Moreover, the proposed method provides much improved CNR for short T2 tissues over the conventional fat saturation method.

To develop and evaluate a sequence in which water excitation with lipid insensitive binomial off-resonant radio frequency excitation (LIBRE) pulses is incorporated into three-dimensional (3D) variable flip angle fast spin echo (LIBRE-vf-FSE) for fat-free and large field of view imaging at 3 Tesla (T). Numerical simulation was conducted to optimize the parameters of LIBRE pulses, including the flip angle, pulse duration, and frequency offset, for maximizing the fat suppression effect of the proposed LIBRE-vf-FSE sequence. The sequence was then implemented at 3 T and assessed in phantoms, lower extremity imaging of 8 healthy volunteers, and head/neck imaging of 5 healthy volunteers. Conventional water excitation (WE) and fat saturation (FatSat) were also performed for comparison. Signal-to-noise ratio (SNR) of fat and contrast-to-noise ratio (CNR) between fat and water were used to evaluate the level of fat suppression. Standard deviation (SD) of SNR was used to evaluate the uniformity of fat suppression. The numerical simulation demonstrated that LIBRE-vf-FSE enables large volume imaging with uniform fat suppression, which was further confirmed by phantom and healthy volunteer experiments. LIBRE provided the lowest fat SNR and offered more uniform fat suppression compared with the WE and FatSat. Specifically, average oil SNRs obtained by LIBRE (1.10 ms, 360 Hz, and 60°), WE, and FatSat were (180.1 vs. 280.2 vs. 811.2) in phantom experiments, and average fat SNRs and SDs in legs obtained by LIBRE (1.10 ms, 360 Hz, and 60°), WE, and FatSat were (85.1 vs. 105.0 vs. 105.1) and (22.4 vs. 27.4 vs. 56.4) in vivo experiments, respectively. The proposed LIBRE-vf-FSE sequence allows for fat suppression and large field of view imaging at 3 T. It could be an alternative approach for fat-free vf-FSE scan. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the feasibility of using a deep learning (DL) model to generate fat-suppression images and detect abnormalities on knee magnetic resonance imaging (MRI) through the fat-suppression image-subtraction method. Material and methods: A total of 45 knee MRI studies in patients with knee disorders and 12 knee MRI studies in healthy volunteers were enrolled. The DL model was developed using 2-dimensional convolutional neural networks for generating fat-suppression images and subtracting generated fat-suppression images without any abnormal findings from those with normal/abnormal findings and detecting/classifying abnormalities on knee MRI. The image qualities of the generated fat-suppression images and subtraction-images were assessed. The accuracy, average precision, average recall, F-measure, sensitivity, and area under the receiver operator characteristic curve (AUROC) of DL for each abnormality were calculated. Results: A total of 2472 image datasets, each consisting of one slice of original T1WI, original intermediate-weighted images, generated fat-suppression (FS)-intermediate-weighted images without any abnormal findings, generated FS-intermediate-weighted images with normal/abnormal findings, and subtraction images between the generated FS-intermediate-weighted images at the same cross-section, were created. The generated fat-suppression images were of adequate image quality. Of the 2472 subtraction-images, 2203 (89.1%) were judged to be of adequate image quality. The accuracies for overall abnormalities, anterior cruciate ligament, bone marrow, cartilage, meniscus, and others were 89.5-95.1%. The average precision, average recall, and F-measure were 73.4-90.6%, 77.5-89.4%, and 78.4-89.4%, respectively. The sensitivity was 57.4-90.5%. The AUROCs were 0.910-0.979. Conclusions: The DL model was able to generate fat-suppression images of sufficient quality to detect abnormalities on knee MRI through the fat-suppression image-subtraction method. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the benefits and challenges of dynamic parallel transmit (pTx) pulses for fat saturation (FS) and water‐excitation (WE), in the context of CEST MRI. Methods: "Universal" kT‐points (for FS) and spiral non‐selective (for WE) trajectories were optimized offline for flip angle (FA) homogeneity. Routines to optimize the pulse shape online, based on the subject's fields maps, were implemented (target FA of 110°/0° for FS, 0°/5° for WE at fat/water frequencies). The pulses were inserted in a CEST sequence with a pTx readout. The different fat suppression schemes and their effects on CEST contrasts were compared in 12 volunteers at 7T. Results: With a 25%‐shorter pulse duration, pTx FS largely improved the FA homogeneity (root‐mean‐square‐error (RMSE) = 12.3° vs. 53.4° with circularly‐polarized mode, at the fat frequency). However, the spectral selectivity was degraded mainly in the cerebellum and close to the sinuses (RMSE = 5.8° vs. 0.2° at the water frequency). Similarly, pTx WE showed a trade‐off between FA homogeneity and spectral selectivity compared to pTx non‐selective pulses (RMSE = 0.9° and 1.1° at the fat and water frequencies, vs. 4.6° and 0.5°). In the brain, CEST metrics were reduced by up to 31.9% at −3.3 ppm with pTx FS, suggesting a mitigated lipid‐induced bias. Conclusion: This clinically compatible implementation of dynamic pTx pulses improved the fat suppression homogeneity at 7T taking into account the subject‐specific B0 heterogeneities online. This study highlights the lipid‐induced biases on the CEST z‐spectrum. The results are promising for body applications where B0 heterogeneities and fat are more substantial. [ABSTRACT FROM AUTHOR]

Objective: To compare the fat suppression effect and imaging quality of Dixon and frequency-selective fat-saturation (Fat- Sat)techniques in orbital T2-weighted imaging (T2WI). Methods: Thirty-five healthy subjects were enrolled，with both orbital Dixon- T2WI (Dixon group)and Fat-Sat-T2WI (Fat-Sat group)scans. The fat suppression effect and overall imaging quality for the two groups were scored. The signal intensity of extraocular muscle and ipsilateral temporal muscle，as well as their signal intensity ratio (SIR)were quantitatively measured. Wilcoxon signed rank test were used to compare the subjective scores between groups. Paired -sample t test were used to compare the signal intensity and SIR between groups. Results: Dixon - T2WI had significantly higher scores of fat suppression effect (3.86±0.36 vs. 2.91±0.56，P ＜ 0.001)and overall imaging quality (3.83±0.38 vs. 3.26±0.56，P ＜ 0.001)as compared to Fat - Sat -T2WI. Dixon -T2WI generated both higher signal intensity of extraocular muscle (362.33±107.73 vs. 286.59±78.84，P ＜ 0.001)and ipsilateral temporal muscle (207.26 ± 63.41 vs. 170.19 ± 51.93，P ＜ 0.001)than Fat - Sat - T2WI. However，there was no significant difference in their SIR between the two groups (1.83±0.54 vs. 1.77±0.49，P=0.239). Conclusion: Dixon-T2WI outperforms Fat-Sat-T2WI in both fat suppression effect and overall imaging quality，without significantly altered SIR. This technique can provide a more reliable diagnosis basis for clinic. [ABSTRACT FROM AUTHOR]

The baseline distortion caused by water and fat signals is a crucial issue in the 1H MRS(I) study of the human brain. This paper suggests an effective and reliable preprocessing technique to calibrate the baseline distortion caused by the water and fat signals exhibited in the MRS spectral signal. For the preprocessing, we designed a T2* (or linewidth within the spectral signal) selective filter for the MRS(I) data based on differential filtering within the frequency domain. The number and types for the differential filtering were determined by comparing the T2* selectivity profile of each differential operator with the T2* profile of the metabolites to be suppressed within the MRS(I) data. In the performance evaluation of the proposed differential filtering, the simulation data for MRS spectral signals were used. Furthermore, the spectral signal of the human 1H MRSI data obtained by 2D free induction decay chemical shift imaging with a typical water suppression technique was also used in the performance evaluation. The absolute values of the average of the filtered dataset were quantitatively analyzed using the LCModel software. With the suggested T2* selective (not frequency selective) filtering technique, in the simulated MRS data, we removed the metabolites from the simulated MRS(I) spectral signal baseline distorted by the water and fat signal observed in the most frequency band. Moreover, in the obtained MRSI data, the quantitative analysis results for the metabolites of interest showed notable improvement in the uncertainty estimation accuracy, the CRLB (Cramer-Rao Lower Bound) levels. [ABSTRACT FROM AUTHOR]

Purpose: Two‐dimensional (2D) echo‐planar radiofrequency (RF) pulses are widely used for reduced field‐of‐view (FOV) imaging in applications such as diffusion‐weighted imaging. However, long pulse durations render the 2D RF pulses sensitive to off‐resonance effects, causing local signal losses in reduced‐FOV images. This work aims to achieve off‐resonance robustness for 2D RF pulses via a sheared trajectory design. Theory and Methods: A sheared 2D RF pulse design is proposed to reduce pulse durations while covering identical excitation k‐space extent as a standard 2D RF pulse. For a given shear angle, the number of sheared trajectory lines is minimized to obtain the shortest pulse duration, such that the excitation replicas are repositioned outside the slice stack to guarantee unlimited slice coverage. A target fat/water signal ratio of 5% is chosen to achieve robust fat suppression. Results: Simulations, imaging experiments on a custom head and neck phantom, and in vivo imaging experiments in the spinal cord at 3 T demonstrate that the sheared 2D RF design provides significant improvement in image quality while preserving profile sharpnesses. In regions with high off‐resonance effects, the sheared 2D RF pulse improves the signal by more than 50% when compared to the standard 2D RF pulse. Conclusion: The proposed sheared 2D RF design successfully reduces pulse durations, exhibiting significantly improved through‐plane off‐resonance robustness, while providing unlimited slice coverage and high fidelity fat suppression. This method will be especially beneficial in regions suffering from a variety of off‐resonance effects, such as spinal cord and breast. [ABSTRACT FROM AUTHOR]

Fat-suppressed images are essential in clinical practice but are often affected by magnetic field inhomogeneity, resulting in poor image quality. We hypothesized that salt (99% sodium chloride [NaCl]) could be used as a magnetic field uniformity assist pad and verified whether salt pads improve magnetic field uniformity and the fat suppression effect in low-field magnetic resonance imaging (MRI) systems. We conducted a small clinical study where coronal 2D fast spin-echo T2-weighted MRI with fat suppression was performed. The subjects were 10 healthy volunteers (six men and four women) with no surgical history, with a mean age of 20.5 years (range, 20–30 years). In the clinical study, we performed physical and visual evaluation by imaging a subject's knee with and without salt pads. The results of the clinical study indicated that the use of salt pads improved the magnetic field uniformity, thus increasing the fat suppression effect. Salt pads improved the homogeneity of the magnetic field and the fat suppression effect in low-field MRI systems. The use of salt pads in low-field MRI systems could provide more accurate fat suppression images. [ABSTRACT FROM AUTHOR]

The conventional gradient-echo steady-state signal model is the basis of various spoiled gradient-echo (SPGR) based quantitative MRI models, including variable flip angle (VFA) MRI and dynamic contrast-enhanced MRI (DCE). However, including preparation pulses, such as fat suppression or saturation bands, disrupts the steady-state and leads to a bias in T 1 and DCE parameter estimates. This work introduces a signal model that improves the accuracy of VFA T 1 -mapping and DCE for interrupted spoiled gradient-echo (I-SPGR) acquisitions. The proposed model was applied to a VFA T 1 -mapping I-SPGR sequence in the Gold Standard T 1 -phantom (3 T), in the brain of four healthy volunteers (3 T), and to an abdominal DCE examination (1.5 T). T 1 -values obtained with the proposed and conventional model were compared to reference T 1 -values. Bland-Altman analysis (phantom) and analysis of variance (in vivo) were used to test whether bias from both methods was significantly different (p = 0.05). The proposed model outperformed the conventional model by decreasing the bias in the phantom with respect to the phantom reference values (mean bias -2 vs. -35% at 3 T) and in vivo with respect to the conventional SPGR (-6 vs. -37% bias in T 1 , p < 0.01). The proposed signal model estimated approximately 48% (depending on baseline T 1 ) higher contrast concentrations in vivo, which resulted in decreased DCE pharmacokinetic parameter estimates of up to 35%. The proposed signal model improves the accuracy of quantitative parameter estimation from disrupted steady-state I-SPGR sequences. It therefore provides a flexible method for applying fat suppression, saturation bands, and other preparation pulses in VFA T 1 -mapping and DCE., (© 2024 The Author(s). NMR in Biomedicine published by John Wiley & Sons Ltd.)

Purpose: To implement a flexible framework, named HydrOptiFrame, for the design and optimization of time-efficient water-excitation (WE) RF pulses using B-spline interpolation, and to characterize their lipid suppression performance., Methods: An evolutionary optimization algorithm was used to design WE RF pulses. The algorithm minimizes a composite loss function that quantifies the fat-water contrast using Bloch equation simulations. In a first study, B-spline interpolated optimized (BSIO) pulses designed with HydrOptiFrame with durations of 1 and 0.76 ms were generated for 3 T and characterized in healthy volunteers' knees. The femoral bone marrow SNR was compared to that obtained with to 1-1 WE and lipid insensitive binomial off resonant excitation (LIBRE) pulses. In a second study, in the heart at 1.5 T, the water-fat contrast ratio and coronary artery vessel length obtained with a 2.56 ms BSIO pulse was compared to 1-1 WE and LIBRE pulses in free-running cardiovascular MR., Results: The 1 ms BSIO pulse resulted in higher fat suppression and lower contrast ratio (CR) in the bone marrow than the state-of-the-art pulses (4.1 ± 0.2 vs. 4.7 ± 0.4 and 4.4 ± 0.3 for the BSIO, the 1-1 WE and LIBRE respectively, p < 0.05 vs. both) at 3 T. At 1.5 T, the BSIO pulse resulted in a higher blood-epicardial fat CR (3.8 ± 1.3 vs. 1.6 ± 0.6 and 2.4 ± 1.1 for the BSIO, 1-1 WE and LIBRE, respectively, p < 0.05 vs. both) and longer traceable left coronary artery vessel length (8.7 ± 1.4 cm vs. 7.0 ± 1.0 cm [p = 0.04] and 7.5 ± 1.2 cm [p = 0.09])., Conclusion: The HydrOptiFrame framework offers a new opportunity to design WE RF pulses that are robust to B 0 inhomogeneity at multiple magnetic field strengths and for variable RF pulse durations., (© 2024 International Society for Magnetic Resonance in Medicine.)

Objective To investigate the efficacy and reliability of Dixon-FLAIR sequence compared with FS-FLAIR sequence for fat suppression in brain MRI. Methods Fourth-six patients with suspected craniocerebral disease were prospectively enrolled and underwent brain MRI including Dixon-FLAIR and FS-FLAIR sequences using a 1.5 T system. Overall image quality and fat suppression uniformity on 4 representative image slices at the levels of maxillary sinus, orbit, frontal sinus, and central sulcus were evaluated using 5-point scale by two observers. The signal-to-noise ratio (SNR) of white matter in the same region of the middle layer of the images from both Dixon-FLAIR and FS-FLAIR was measured. Results The scores of fat suppression effect by Dixon-FLAIR on overall image quality (3, 5; average score: 4) with agreement Kappa coefficients between the two observers of 0.823, maxillary sinus (1, 5; 3; 0.890), orbit (1, 5; 4; 0.886), frontal sinus (3, 5; 4; 0.803), and central sulcus (3, 5; 4; 0.826) image slices were significantly higher than that of FS-FLAIR on overall image quality (1, 3; 1.5; 0.926), maxillary sinus (1, 2; 1; 1.000), orbit (1, 3; 2; 0.823), frontal sinus (1, 3; 1; 0.819), and central sulcus (1, 4; 3; 0.924) image slices (all P<0.05). There was also good agreement between the two observers with all κ>0.8 in assessing the effect of fat suppression. The SNR of Dixon-FLAIR (195.44±37.96) was significantly (P<0.05) better than that of FS-FLAIR (165.88± 35.31) sequence. Conclusion Dixon-FLAIR can achieve better SNR with better fat suppression uniformity and can replace FS-FLAIR sequence in brain MRI. [ABSTRACT FROM AUTHOR]

Purpose: To compare apparent diffusion coefficients (ADCs) of bone marrow on diffusion-weighted imaging (DWI) between two fat-suppression techniques, and to evaluate the association between bonemarrow ADCs and the proton density fat fraction (PDFF). Methods: Seventy-seven patients underwent whole-bodyDWI with short-inversion time inversion-recovery (STIR) (DWISTIR) and/or STIR + selective water-excitation (spectral-spatial RF [SSRF]) (DWISTIR+SSRF). ADCs of lumbar vertebrae (L3 and L4) were compared between DWISTIR and DWISTIR+SSRF, and correlated with the PDFF. Results: Lumbar ADCs obtained by DWISTIR and DWISTIR+SSRF were significantly correlated (L3: r = 0.90, P < 0.0001, L4: r = 0.90, P < 0.0001). Lumbar ADCs (× 10-6 mm²/s) obtained by DWISTIR were significantly lower than those by DWISTIR+SSRF (L3: 479±137 and 490±148, P < 0.05, L4: 456±114 and 471±118, P < 0.005). Residual fat signals were more clearly observed on DWISTIR than on DWISTIR+SSRF. The ADCs of L3 obtained by DWISTIR and DWISTIR+SSRF exhibited significant positive correlations with the PDFF (r = 0.51, P < 0.0001, and r = 0.45, P < 0.0001, respectively), and the ADCs of L4 obtained by DWISTIR and DWISTIR+SSRF exhibited significantly positive correlations with the PDFF (r = 0.40, P < 0.0005, and r = 0.40, P < 0.0005, respectively). Conclusion: Irrespective of different fat-suppressionmethods, lumbar ADCs were positively correlated with the PDFF, being inconsistent with previous studies. Lumbar ADCs obtained by DWISTIR were significantly lower than those obtained by DWISTIR+SSRF, probably due to residual fat signals on DWISTIR. However, this difference (< 4%) did not explain the positive correlation between lumbar ADC and PDFF. [ABSTRACT FROM AUTHOR]

The baseline distortion caused by water and fat signals is a crucial issue in the 1H MRS(I) study of the human brain. This paper suggests an effective and reliable preprocessing technique to calibrate the baseline distortion caused by the water and fat signals exhibited in the MRS spectral signal. For the preprocessing, we designed a T2* (or linewidth within the spectral signal) selective filter for the MRS(I) data based on differential filtering within the frequency domain. The number and types for the differential filtering were determined by comparing the T2* selectivity profile of each differential operator with the T2* profile of the metabolites to be suppressed within the MRS(I) data. In the performance evaluation of the proposed differential filtering, the simulation data for MRS spectral signals were used. Furthermore, the spectral signal of the human 1H MRSI data obtained by 2D free induction decay chemical shift imaging with a typical water suppression technique was also used in the performance evaluation. The absolute values of the average of the filtered dataset were quantitatively analyzed using the LCModel software. With the suggested T2* selective (not frequency selective) filtering technique, in the simulated MRS data, we removed the metabolites from the simulated MRS(I) spectral signal baseline distorted by the water and fat signal observed in the most frequency band. Moreover, in the obtained MRSI data, the quantitative analysis results for the metabolites of interest showed notable improvement in the uncertainty estimation accuracy, the CRLB (Cramer-Rao Lower Bound) levels.

Purpose: To develop a true single shot turbo spin echo (SShTSE) acquisition with Dixon for robust T2‐weighted abdominal imaging with uniform fat and water separation at 3T. Methods: The in‐phase (IP) and out‐of‐phase (OP) echoes for Dixon processing were acquired in the same repetition time of a SShTSE using partial echoes. A phase‐preserved bi‐directional homodyne reconstruction was developed to compensate the partial echo and the partial phase encoding of SShTSE. With IRB approval, the SShTSE‐Dixon was compared against standard SShTSE, without and with fat suppression using spectral adiabatic inversion recovery (SPAIR) in 5 healthy volunteers and 5 patients. The SNR and contrast ratio (CR) of spleen to liver were compared among different acquisitions. Results: The bi‐directional homodyne reconstruction successfully minimized ringing artifacts because of partial acquisitions. SShTSE‐Dixon achieved uniform fat suppression compared to SShTSE‐SPAIR with fat suppression failures of 1/10 versus 10/10 in the axial plane and 0/5 versus 5/5 in the coronal plane, respectively. The SNRs of the liver (12.2 ± 4.9 vs. 11.7 ± 5.2; P =.76) and spleen (25.9 ± 11.6 vs. 23.7 ± 9.7; P =.14) were equivalent between fat‐suppressed images (SShTSE‐Dixon water‐only and SShTSE‐SPAIR). The SNRs of liver (14.4 ± 5.7 vs. 13.4 ± 5.0; P =.60) and spleen (26.5 ± 10.1 vs. 25.7 ± 8.5; P =.56) were equivalent between non‐fat‐suppressed images (SShTSE‐Dixon IP and SShTSE). The CRs of spleen to liver were also similar between fat‐suppressed images (2.6 ± 0.4 vs. 2.5 ± 0.5; P =.92) and non‐fat‐suppressed images (2.3 ± 0.6 vs. 2.2 ± 0.4; P =.84). Conclusion: SShTSE‐Dixon generates robust abdominal T2‐weighted images at 3T with and without uniform fat suppression, along with perfectly co‐registered fat‐only images in a single acquisition. [ABSTRACT FROM AUTHOR]

Purpose: Designing a new T2‐preparation (T2‐Prep) module to simultaneously provide robust fat suppression and efficient T2 preparation without requiring an additional fat‐suppression module for T2‐weighted imaging at 3T. Methods: The tip‐down radiofrequency (RF) pulse of an adiabatic T2‐Prep module was replaced by a custom‐designed RF‐excitation pulse that induces a phase difference between water and fat, resulting in a simultaneous T2 preparation of water signals and the suppression of fat signals at the end of the module (a phaser adiabatic T2‐Prep). Numerical simulations and in vitro and in vivo electrocardiogram (ECG)‐triggered navigator‐gated acquisitions of the human heart were performed. Blood, myocardium, and fat signal‐to‐noise ratios and right coronary artery vessel sharpness were compared against previously published adiabatic T2‐Prep approaches. Results: Numerical simulations predicted an increased fat‐suppression bandwidth and decreased sensitivity to transmit magnetic field inhomogeneities using the proposed approach while preserving the water T2‐Prep capabilities. This was confirmed by the tissue signals acquired in the phantom and the in vivo images, which show similar blood and myocardium signal‐to‐noise ratio, contrast‐to‐noise ratio, and significantly reduced fat signal‐to‐noise ratio compared with the other methods. As a result, the right coronary artery conspicuity was significantly increased. Conclusion: A novel fat‐suppressing T2‐Prep method was developed and implemented that showed robust fat suppression and increased vessel sharpness compared with conventional techniques while preserving its T2‐Prep capabilities. [ABSTRACT FROM AUTHOR]

Abstract Introduction The objective of this study was to evaluate the effect on diagnostic image quality and acquisition time utilising a DIXON sequence to replace two standard proton density (PD) fat saturation (FS) sequences in routine magnetic resonance (MR) evaluation of the knee. Methods Thirty‐one consecutive patients referred for an MR examination of the knee were examined using the routine departmental protocol along with the addition of a DIXON sequence. The sequences were all evaluated by a senior radiologist and feedback provided via both written and scored responses. The sequences were then repackaged for two additional reviewers with the sagittal PD FS (Chemical Shift Selective Fat Saturation or CHESS) and sagittal PD removed and replaced with the DIXON (fat suppressed and in‐phase, respectively) sequence equivalents. Scored and written responses were tabled and reviewed to assess the suitability of sequence replacement. Results The DIXON‐based images were judged as being comparable replacements for the sagittal PD fat sat and PD sequences. There was no report of any loss in diagnostic confidence across the 31 patients (total of 32 knees) with a time saving of just over 10% gained. The most common issues raised affecting image quality, though not affecting diagnostic attributes, were patient motion and a minor chemical shift artefact. Conclusion The use of the DIXON technique in place of the PD sequences was of equivalent diagnostic quality with’good’ to ‘outstanding’ fat suppression observed for the majority of cases using the DIXON sequence with an incremental time saving obtained.

Abstract Background Robust and homogeneous lipid suppression is mandatory for coronary artery cardiovascular magnetic resonance (CMR) imaging since the coronary arteries are commonly embedded in epicardial fat. However, effective large volume lipid suppression becomes more challenging when performing radial whole-heart coronary artery CMR for respiratory self-navigation and the problem may even be exacerbated at increasing magnetic field strengths. Incomplete fat suppression not only hinders a correct visualization of the coronary vessels and generates image artifacts, but may also affect advanced motion correction methods. The aim of this study was to evaluate a recently reported lipid insensitive CMR method when applied to a noncontrast self-navigated coronary artery CMR acquisitions at 3 T, and to compare it to more conventional fat suppression techniques. Methods Lipid insensitive binomial off resonant excitation (LIBRE) radiofrequency excitation pulses were included into a self-navigated 3D radial GRE coronary artery CMR sequence at 3 T. LIBRE was compared against a conventional CHESS fat saturation (FS) and a binomial 1–180°-1 water excitation (WE) pulse. First, fat suppression of all techniques was numerically characterized using Matlab and experimentally validated in phantoms and in legs of human volunteers. Subsequently, free-breathing self-navigated coronary artery CMR was performed using the LIBRE pulse as well as FS and WE in ten healthy subjects. Myocardial, arterial and chest fat signal-to-noise ratios (SNR), as well as coronary vessel conspicuity were quantitatively compared among those scans. Results The results obtained in the simulations were confirmed by the experimental validations as LIBRE enabled near complete fat suppression for 3D radial imaging in vitro and in vivo. For self-navigated whole-heart coronary artery CMR at 3 T, fat SNR was significantly attenuated using LIBRE compared with conventional FS. LIBRE increased the right coronary artery (RCA) vessel sharpness significantly (37 ± 9% (LIBRE) vs. 29 ± 8% (FS) and 30 ± 8% (WE), both p

An efficient multi-slice inversion–recovery EPI (MS-IR-EPI) sequence for fast, high spatial resolution, quantitative T1 mapping is presented, using a segmented simultaneous multi-slice acquisition, combined with slice order shifting across multiple acquisitions. The segmented acquisition minimises the effective TE and readout duration compared to a single-shot EPI scheme, reducing geometric distortions to provide high quality T1 maps with a narrow point-spread function. The precision and repeatability of MS-IR-EPI T1 measurements are assessed using both T1-calibrated and T2-calibrated ISMRM/NIST phantom spheres at 3 and 7 T and compared with single slice IR and MP2RAGE methods. Magnetization transfer (MT) effects of the spectrally-selective fat-suppression (FS) pulses required for in vivo imaging are shown to shorten the measured in-vivo T1 values. We model the effect of these fat suppression pulses on T1 measurements and show that the model can remove their MT contribution from the measured T1, thus providing accurate T1 quantification. High spatial resolution T1 maps of the human brain generated with MS-IR-EPI at 7 T are compared with those generated with the widely implemented MP2RAGE sequence. Our MS-IR-EPI sequence provides high SNR per unit time and sharper T1 maps than MP2RAGE, demonstrating the potential for ultra-high resolution T1 mapping and the improved discrimination of functionally relevant cortical areas in the human brain.

Aim: The study aimed to evaluate the long‐term recurrence rates and survival following upfront laparoscopic total mesorectal excision (TME) for rectal adenocarcinoma. Patient and Methods: This was a retrospective cohort of 94 patients with rectal adenocarcinoma undergoing upfront radical resection in New Territories West Cluster between 2010 and 2015. Tumours with safe circumferential resection margin (>1 mm) on magnetic resonance imaging (MRI) staging were selected for upfront surgery. Demographic data, tumour characteristics, operative details, and histopathological and postoperative outcomes were collected from patients' records. The primary outcome was local recurrence. Secondary outcomes were distant recurrence and overall (OS) and disease‐free survival (DFS). Results: A total of 224 patients were diagnosed with rectal adenocarcinoma, of which 94 received upfront surgery after a multidisciplinary team discussion by surgeons and oncologists. The median follow‐up period after surgery was 60 months (range 4.7‐60.9 months), with four patients lost to follow‐up. Six patients (6.3%) developed local recurrence (two with isolated local recurrence and four with local and distant recurrence). Twelve patients (12.8%) experienced distant recurrence. The 5‐year OS and DFS rates were 84.3% and 76.2%, respectively. Possible prognostic factors for local recurrence (including distal tumour level ≤ 5 cm, clinical nodal stage, clinical threatened margin, pathological stage, harvested lymph nodes <12, distal margin <1 cm, positive extramural venous invasion, and circumferential resection margin) were evaluated by multivariable logistic regression, and were shown to be insignificant. Conclusion: Upfront laparoscopic TME for MRI‐selected rectal cancer patients can achieve favourable oncological outcomes in our centre. Routine neoadjuvant treatment for all T3 or nodal positive disease is not necessary. [ABSTRACT FROM AUTHOR]

Purpose: The recently introduced inhomogeneous magnetization transfer (ihMT) method has predominantly been applied for imaging the central nervous system. Future applications of ihMT, such as in peripheral nerves and muscles, will involve imaging in the vicinity of adipose tissues. This work aims to systematically investigate the partial volume effect of fat on the ihMT signal and to propose an efficient fat‐separation method that does not interfere with ihMT measurements. Methods: First, the influence of fat on ihMT signal was studied using simulations. Next, the ihMT sequence was combined with a multi‐echo Dixon acquisition for fat separation. The sequence was tested in 9 healthy volunteers using a 3T human scanner. The ihMT ratio (ihMTR) values were calculated in regions of interest in the brain and the spinal cord using standard acquisition (no fat saturation), water‐only, in‐phase, and out‐of‐phase reconstructions. The values obtained were compared with a standard fat suppression method, spectral presaturation with inversion recovery. Results: Simulations showed variations in the ihMTR values in the presence of fat, depending on the TEs used. The IhMTR values in the brain and spinal cord derived from the water‐only ihMT multi‐echo Dixon images were in good agreement with values from the unsuppressed sequence. The ihMT–spectral presaturation with inversion recovery combination resulted in 24%‐35% lower ihMTR values compared with the standard non‐fat‐suppressed acquisition. Conclusion: The presence of fat within a voxel affects the ihMTR calculations. The IhMT multi‐echo Dixon method does not compromise the observable ihMT effect and can potentially be used to remove fat influence in ihMT. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate 3D UTE bicomponent imaging of cortical bone ex vivo and in vivo using a newly designed soft–hard composite pulse for excitation. Methods: Chemical shift artifacts, presenting as fat–water oscillation or combination‐induced signal oscillation, significantly reduce the accuracy of quantitative UTE bicomponent analysis of cortical bone. To achieve fat suppression for more reliable bicomponent analysis, a newly developed soft–hard excitation pulse was used with UTE imaging and compared with a single rectangular pulse excitation without and with a conventional fat saturation (FatSat) module. These 3 sequences were applied to 8 bovine bone samples without marrow fat, 3 bovine bone samples with marrow fat, and tibial midshafts of 5 healthy human volunteers. Bicomponent analyses were performed in both ex vivo and in vivo studies. Results: The soft–hard pulse provided comparable fat suppression, but much reduced bone signal attenuation compared with the FatSat module. Better bicomponent T2∗ fitting was also achieved with the soft–hard excitation pulse because it greatly reduced chemical shift artifacts and outperformed the single rectangular pulse without or with FatSat. Although the FatSat module reduced fat signals and related fat–water oscillation, the water signals were significantly attenuated with more than 40% reduction due to direction saturation. For the inner layer of tibial midshaft in healthy volunteers, fitting errors increased from 3.78% for the soft–hard pulse to 11.43% and 5.16%, respectively, for the single rectangular pulse without and with the FatSat module. Conclusion: The 3D UTE sequence with a new soft–hard excitation pulse allows more reliable bicomponent imaging of cortical bone. [ABSTRACT FROM AUTHOR]

Spectrally selective fat saturation (FatSat) sequence is commonly used to suppress signal from adipose tissue. Conventional SINC-shaped pulses are sensitive to B 0 off-resonance and B 1 + offset. Uniform fat saturation with large spatial coverage is especially challenging for the body and breast MRI. The aim of this study is to develop spectrally selective FatSat pulses that offer more immunity to B 0 /B 1 + field inhomogeneities than SINC pulses and evaluate them in bilateral breast imaging at 3 T. Optimized composite pulses (OCP) were designed based on the optimal control theory with robustness to a targeted B 0 / B 1 + conditions. OCP pulses also allows flexible flip angles to meet different requirements. Comparisons with the vendor-provided SINC pulses were conducted by numerical simulation and in vivo scans using a 3D T 1 -weighted (T 1 w) gradient-echo (GRE) sequence with coverage of the whole-breast. Simulation revealed that OCP pulses yielded almost half of the transition band and much less sensitivity to B 1 + inhomogeneity compared to SINC pulses with B 0 off-resonance within ±200 Hz and B 1 + scale error within ±0.3 (P < 0.001). Across five normal subjects, OCP FatSat pulses produced 25–41% lower residual fat signals (P < 0.05) with 27–36% less spatial variation (P < 0.05) than SINC. In contrast to conventional SINC-shaped pulses, the newly designed OCP FatSat pulses mitigated challenges of wide range of B 0 / B 1 + field inhomogeneities and achieved more uniform fat suppression in bilateral breast T 1 w imaging at 3 T. [ABSTRACT FROM AUTHOR]

The acquisition of images with suppression of the fat signal is very useful in clinical practice and can be achieved in a variety of sequences. The Dixon technique, unlike other fat suppression techniques, allows the signal of fat to be suppressed in the postprocessing rather than during acquisition, as well as allowing the visualization of maps showing the distribution of water and fat. This review of the Dixon technique aims to illustrate the basic physical principles, to compare the technique with other magnetic resonance imaging sequences for fat suppression or fat quantification, and to describe its applications in the study of diseases of the musculoskeletal system. Many variants of the Dixon technique have been developed, providing more consistent separation of the fat and water signals, as well as allowing correction for many confounding factors. It allows homogeneous fat suppression, being able to be acquired in combination with several other sequences, as well as with different weightings. The technique also makes it possible to obtain images with and without fat suppression from a single acquisition. In addition, the Dixon technique can be used as a quantitative method, allowing the proportion of tissue fat to be determined, and, in more updated versions, can quantify tissue iron. [ABSTRACT FROM AUTHOR]

Purpose: The combination of modified Dixon (mDixon) and periodically rotated overlapping parallel lines with enhanced reconstruction sequence with two interleaved echoes, which promotes uniform fat-suppression and motion insensitivity, has recently become available for commercial magnetic resonance imaging (MRI) scanners. To compare the robustness of this combination sequence with that of standard Cartesian mDixon sequence for fat-suppressed T2-weighted imaging in clinical head and neck MRI. Methods: Fifty patients with head and neck tumors were involved this study. All patients underwent MRI using both the combination and standard sequences. Two radiologists independently scored motion artifacts and water-fat separation error using a 4-point scale (1, unacceptable; 4, excellent). Furthermore, comprehensive comparative evaluation was performed using a 5-point scale (1, substantially inferior; 5, substantially superior). Data were statistically analyzed using the Wilcoxon signed-rank test. Results: In the motion artifact assessment, ratings of 3 or 4 points were assigned to 45% (observer-1, 58.0%; observer-2, 32.0%) and 97% (100%; 94.0%) of images for the standard and combination sequences, respectively (P < 0.001). For the water-fat separation error assessment, ratings of 3 or 4 points were assigned to 100% (100%; 100%) and 85% (84.0%; 86.0%) of images, respectively (P < 0.001). In the comprehensive evaluation, of the 100 cases (observer-1, 50; observer-2, 50), 96 were rated at four or five points. In cases with slight or no motion artifacts and water-fat separation errors, the combination sequence was superior to the standard sequence in term of noise and sharpness, and equal in terms of contrast. Conclusion: Although water-fat separation errors increased significantly in the combination sequence, most of these were acceptable. The significantly decreased motion artifacts in the combination sequence significantly improved image quality overall. [ABSTRACT FROM AUTHOR]

Purpose: To implement, optimize, and characterize lipid‐insensitive binomial off‐resonant RF excitation (LIBRE) pulses for fat‐suppressed fully self‐gated free‐running 5D cardiac MRI. Methods: Bloch equation simulations were used to optimize LIBRE parameter settings in non‐interrupted bSSFP prior to in vitro validation. Thus, optimized LIBRE pulses were subsequently applied to free‐running coronary MRA in 20 human adult subjects, where resulting images were quantitatively compared to those obtained with non‐fat‐suppressing excitation (SP), conventional 1‐2‐1 water excitation (WE), and a previously published interrupted free‐running (IFR) sequence. SAR and scan times were recorded. Respiratory‐and‐cardiac‐motion‐resolved images were reconstructed with XD‐GRASP, and contrast ratios, coronary artery detection rate, vessel length, and vessel sharpness were computed. Results: The numerically optimized LIBRE parameters were successfully validated in vitro. In vivo, LIBRE had the lowest SAR and a scan time that was similar to that of WE yet 18% shorter than that of IFR. LIBRE improved blood–fat contrast when compared to SP, WE, and IFR, vessel detection relative to SP and IFR, and vessel sharpness when compared to WE and IFR (for example, for the left main and anterior descending coronary artery, 51.5% ± 10.2% [LIBRE] versus 42.1% ± 6.8% [IFR]). Vessel length measurements remained unchanged for all investigated methods. Conclusion: LIBRE enabled fully self‐gated non‐interrupted free‐running 5D bSSFP imaging of the heart at 1.5T with suppressed fat signal. Measures of image quality, vessel conspicuity, and scan time compared favorably to those obtained with the more conventional non‐interrupted WE and the previously published IFR, while SAR reduction offers added flexibility. [ABSTRACT FROM AUTHOR]

Objective To compare the image effects between 3D CUBE T1-weighted sequence images with and without fat suppression in high resolution intracranial magnetic resonance imaging. Methods By using GE3. OT MRI and 3D CUBE technology, 105 patients with middle cerebral artery stenosis were scanned with 3D CUBE T1-weighted sequence images with and without fat suppression, respectively. The image signal strength, signal-to-noise ratio and contrast signal-tonoise ratio of each region of interest of two different scan sequences were calculated and compared, and images of different sequences, the plaque, and lumen area were measured. The image quality of these two sequences was scored by 2 physicians for twice and their consistency was analyzed. Results The signal intensity, signal-to-noise ratio and contrast signalto- noise ratio of each region of interest of the 3D CUBE T1 without fat suppression sequence were all higher than those of the 3D CUBE T1 with fat suppression sequence, while the noise level was lower than that of the 3D CUBE T1 fat suppression sequence, with statistically significant differences (all P < 0. 05). There was no statistically significant difference in the vascular cross section and lumen area measured by the two physicians (both P > 0. 05), but there was a statistically significant difference in the plaque area measured (P < 0. 05). Both 3D CUBE T1 with and without fat suppression sequences could clearly display MCA plaques, but the signal performance was different. There were 12 patients with different plaque signals on the two sequences, showing high or slightly high signals in the 3D CUBE T1 without fat suppression sequence, and showing equal signals in the 3D CUBE T1 with fat suppression. There was no statistically significant difference in lumen display scores between the two sequences (P > 0. 05) . Compared with 3D CUBE Tl with fat suppression sequence, 3D CUBE Tl without fat suppression sequence had higher scores in artifact, noise, image contrast, vascular display, vascular wall and surrounding tissue comparison, plaque display, and plaque and vascular wall comparison (all P < 0. 05) . There was a good consistency in the scores of the first and second images between the two physicians, and there was a good consistency in the scores of the first and second images between the two physicians. Conclusions In the case of high resolution vascular wall imaging in patients with middle cerebral artery stenosis, 3D CUBE Tl without fat suppression sequence has lower noise, higher signal-to-noise ratio and higher tissue resolution than Tl with fat suppression sequence, which has more advantages in the display and resolution of vascular wall and plaques. [ABSTRACT FROM AUTHOR]

The aim of the present study was to evaluate magnetic resonance venography (MRV) scanned by breath-hold volume interpolated body examination with spectral fat saturation (VIBE-fs), combined with Dixon fat-suppressed VIBE (VIBE-Dixon) by using a 1.5T MR scanner for detecting deep venous thrombosis (DVT) compared with duplex sonography. A total of 31 patients with DVT were identified using duplex sonography and were enrolled in the present study for MRV examination, from the inferior vena cava to the ankle level after injection of gadopentetate dimeglumine. Venous segment-to-segment comparison was assessed for DVT detection between MRV and duplex sonography. A total of two radiologists separately performed subjective image quality assessment using a 5-point scale. Cohen's κ coefficient, Wilcoxon rank sum test and intraclass correlation coefficient values were used for statistical analysis. Of the 303 evaluated vein segments, duplex sonography identified 119 (39.3%; 119/303) venous segments with thrombus, while MRV detected 170 (56.1%; 170/303) venous segments with thrombus. The diagnostic agreement rate of DVT between duplex sonography and MRV was poor in the deep femoral vein and anterior tibial veins, while it was excellent in the inferior vena cava (IVC), common iliac vein, external iliac vein, femoral vein, popliteal vein, posterior tibial veins and peroneal veins. In addition, poor reliability was detected in the deep femoral vein, anterior tibial veins and peroneal veins, but good to excellent reliability was observed in IVC, common iliac vein, external iliac vein, femoral vein, popliteal vein and posterior tibial veins. Furthermore, image quality scores of each venous segment between the two radiologists indicated no statistical difference. Therefore, MRV scanned using VIBE-fs for the suprainguinal and VIBE-Dixon for the infrainguinal region may be a useful method for detecting DVT compared with duplex sonography. The results of present study proved this MR protocol to be a beneficial alternative imaging modality for the detection of DVT when duplex sonography is inadequate or not able to be performed. [ABSTRACT FROM AUTHOR]

Purpose: The application of amide proton transfer (APT) CEST MRI for diagnosis of breast cancer is of emerging interest. However, APT imaging in the human breast is affected by the ubiquitous fat signal preventing a straightforward application of existing acquisition protocols. Although the spectral region of the APT signal does not coincide with fat resonances, the fat signal leads to an incorrect normalization of the Z‐spectrum, and therefore to distorted APT effects. In this study, we propose a novel normalization for APT‐CEST MRI that corrects for fat signal–induced artifacts in the postprocessing without the need for application of fat saturation schemes or water–fat separation approaches. Methods: The novel normalization uses the residual signal at the spectral position of the direct water saturation to estimate the fat contribution. A comprehensive theoretical description of the normalization for an arbitrary phase relation of the water and fat signal is provided. Functionality and applicability of the proposed normalization was demonstrated by in vitro and in vivo experiments. Results: In vitro, an underestimation of the conventional APT contrast of approximately −1.2% per 1% fat fraction was observed. The novel normalization yielded an APT contrast independent of the fat contribution, which was also independent of the water‐fat phase relation. This allowed APT imaging in patients with mamma carcinoma corrected for fat signal contribution, field inhomogeneities, spillover dilution, and water relaxation effects. Conclusion: The proposed normalization increases the specificity of APT imaging in tissues with varying fat content and represents a time‐efficient and specific absorption rate–efficient alternative to fat saturation and water–fat separation approaches. [ABSTRACT FROM AUTHOR]

Free-running 5D whole-heart coronary MR angiography (MRA) is gaining in popularity because it reduces scanning complexity by removing the need for specific slice orientations, respiratory gating, or cardiac triggering. At 3T, a gradient echo (GRE) sequence is preferred in combination with contrast injection. However, neither the injection scheme of the gadolinium (Gd) contrast medium, the choice of the RF excitation angle, nor the dedicated image reconstruction parameters have been established for 3T GRE free-running 5D whole-heart coronary MRA. In this study, a Gd injection scheme, RF excitation angles of lipid-insensitive binominal off-resonance RF excitation (LIBRE) pulse for valid fat suppression and continuous data acquisition, and compressed-sensing reconstruction regularization parameters were optimized for contrast-enhanced free-running 5D whole-heart coronary MRA using a GRE sequence at 3T. Using this optimized protocol, contrast-enhanced free-running 5D whole-heart coronary MRA using a GRE sequence is feasible with good image quality at 3T.

Introduction: Magnetic resonance imaging (MRI) staging scans are critical for the diagnosis and treatment of patients with nasopharyngeal cancer (NPC). We aimed to evaluate the application value of LAVA-Flex and T1WI-IDEAL sequences in MRI staging scans., Methods: Eighty-four newly diagnosed NPC patients underwent both LAVA-Flex and T1WI-IDEAL sequences during MRI examinations. Two radiologists independently scored the acquisitions of image quality, fat suppression quality, artifacts, vascular and nerve display. The obtained scores were compared using the Wilcoxon signed rank test. According to the signal intensity (SI) measurements, the uniformity of fat suppression, contrast between tumor lesions and subcutaneous fat tissue, and signal-to-noise ratio (SNR) were compared by the paired t-test., Results: Compared to the T1WI-IDEAL sequence, LAVA-Flex exhibited fewer artifacts ( P <0.05), better visualization of nerves and vessels ( P <0.05), and performed superior in the fat contrast ratio of the primary lesion and metastatic lymph nodes (0.80 vs . 0.52, 0.81 vs . 0.56, separately, P <0.001). There was no statistically significant difference in overall image quality, tumor signal-to-noise ratio (SNR), muscle SNR, and the detection rate of lesions between the two sequences ( P >0.05). T1WI-IDEAL was superior to LAVA-Flex in the evaluation of fat suppression uniformity ( P <0.05)., Discussion: LAVA-Flex sequence provides satisfactory image quality and better visualization of nerves and vessels for NPC with shorter scanning times., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Peng, Chen, Yu, Lin, Lin, Zheng, Fu, Chen, Zheng, Zhan and Chen.)