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It is beneficial for both hospitals and patients to accelerate MRI scanning. Recently, a new fast MRI technique based on CS was proposed. However, the reconstruction quality and computation time of CS-MRI did not meet the standard of clinical use. Therefore, we proposed a novel algorithm based on three successful components: the sparsity of EWT, the rapidness of FISTA, and the excellent tuning in SISTA. The proposed method was dubbed Exponential Wavelet Iterative Shrinkage/Threshold Algorithm (EWISTA). Experiments over four kinds of MR images (brain, ankle, knee, and ADHD) indicated that the proposed EWISTA showed better reconstruction performance than the state-of-the-art algorithms such as FCSA, ISTA, FISTA, SISTA, and EWT-ISTA. Moreover, EWISTA was faster than ISTA and EWT-ISTA, but slightly slower than FCSA, FISTA and SISTA.

PurposeTo design parallel transmit (pTx) simultaneous multislice (SMS) spokes pulses with explicit control for peak power and local and global specific absorption rate (SAR). MethodsWe design SMS pTx least-squares and magnitude least squares spokes pulses while constraining local SAR using the virtual observation points (VOPs) compression of SAR matrices. We evaluate our approach in simulations of a head (7T) and a body (3T) coil with eight channels arranged in two z-rows. ResultsFor many of our simulations, control of average power by Tikhonov regularization of the SMS pTx spokes pulse design yielded pulses that violated hardware and SAR safety limits. On the other hand, control of peak power alone yielded pulses that violated local SAR limits. Pulses optimized with control of both local SAR and peak power satisfied all constraints and therefore had the best excitation performance under limited power and SAR constraints. These results extend our previous results for single slice pTx excitations but are more pronounced because of the large power demands and SAR of SMS pulses. ConclusionsExplicit control of local SAR and peak power is required to generate optimal SMS pTx excitations satisfying both the system's hardware limits and regulatory safety limits. Magn Reson Med 73:1946-1953, 2015. (c) 2014 Wiley Periodicals, Inc.

Whole brain segmentation from structural MRI-T1 scan is a prerequisite for most morphological analyses, but requires hours of processing time and therefore delays the availability of image markers after scan acquisition. We introduced a fully convolution neural network (F-CNN) that segments a brain scan in several seconds [1]. Training deep F-CNNs for semantic image segmentation requires access to abundant labeled data.

Gradient-echo echo-planar imaging (EPI) is the primary method of choice in functional MRI and other methods relying on fast MRI to image brain activation and connectivity. However, the high susceptibility of EPI towards B0 magnetic field inhomogeneity poses serious challenges. Conventional magnetic field shimming with low-order spherical harmonic (SH) functions is capable of compensating shallow field distortions, but performs poorly for global brain shimming or on specific areas with strong susceptibility-induced B0 distortions such as the prefrontal cortex (PFC). Excellent B0 homogeneity has been demonstrated recently in the human brain at 7 Tesla with the DYNAmic Multi-coIl TEchnique (DYNAMITE) for magnetic field shimming (J Magn Reson (2011) 212:280-288). Here, we report the benefits of DYNAMITE shimming for multi-slice EPI and T2* mapping. A standard deviation of 13Hz was achieved for the residual B0 distribution in the human brain at 7 Tesla with DYNAMITE shimming and was 60% lower compared to conventional shimming that employs static zero through third order SH shapes. The residual field inhomogeneity with SH shimming led to an average 8mm shift at acquisition parameters commonly used for fMRI and was reduced to 1.5-3mm with DYNAMITE shimming. T2* values obtained from the prefrontal and temporal cortices with DYNAMITE shimming were 10-50% longer than those measured with SH shimming. The reduction of the confounding macroscopic B0 field gradients with DYNAMITE shimming thereby promises improved access to the relevant microscopic T2* effects. The combination of high spatial resolution and DYNAMITE shimming allows largely artifact-free EPI and T2* mapping throughout the brain, including prefrontal and temporal lobe areas. DYNAMITE shimming is expected to critically benefit a wide range of MRI applications that rely on excellent B0 magnetic field conditions including EPI-based fMRI to study various cognitive processes and assessing large-scale brain connectivity in vivo. As such, DYNAMITE shimming has the potential to replace conventional SH shim systems in human MR scanners.

Compressed sensing magnetic resonance imaging (CS-MRI) enables fast acquisition, which is highly desirable for numerous clinical applications. This can not only reduce the scanning cost and ease patient burden, but also potentially reduce motion artefacts and the effect of contrast washout, thus yielding better image quality. Different from parallel imaging-based fast MRI, which utilizes multiple coils to simultaneously receive MR signals, CS-MRI breaks the Nyquist-Shannon sampling barrier to reconstruct MRI images with much less required raw data. This paper provides a deep learning-based strategy for reconstruction of CS-MRI, and bridges a substantial gap between conventional non-learning methods working only on data from a single image, and prior knowledge from large training data sets. In particular, a novel conditional Generative Adversarial Networks-based model (DAGAN)-based model is proposed to reconstruct CS-MRI. In our DAGAN architecture, we have designed a refinement learning method to stabilize our U-Net based generator, which provides an end-to-end network to reduce aliasing artefacts. To better preserve texture and edges in the reconstruction, we have coupled the adversarial loss with an innovative content loss. In addition, we incorporate frequency-domain information to enforce similarity in both the image and frequency domains. We have performed comprehensive comparison studies with both conventional CS-MRI reconstruction methods and newly investigated deep learning approaches. Compared with these methods, our DAGAN method provides superior reconstruction with preserved perceptual image details. Furthermore, each image is reconstructed in about 5 ms, which is suitable for real-time processing.

Hybrid imaging using various radiopharmaceuticals is currently essential not only in detection and therapy response monitoring of tumors, but also in assessment of inflammatory or systemic diseases. Combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) is still relatively new method with great prospects of comprehensive assessment using anatomical and multiple functional information. However, benefits of PET/MRI in thorax, abdomen and retroperitoneum are not completely defined. Breathing movements affect imaging of thoracic, abdominal and retroperitoneal organs and pathological structures using PET and MRI. Fast MRI sequences are performed using breath-hold technique; however, acquisition of longer sequences and PET scanning need to be breathing-synchronized. Review article summarizes concrete PET/MRI protocols and importance of concrete MRI sequences and radiopharmaceuticals in different pathological lesions with focus on benefit of breathing-synchronized techniques.

International audience; The volume fraction of water related to myelin (f my) is a promising MRI index for in vivo assessment of brain myelination, that can be derived from multi-component analysis of T1 and T2 relaxometry signals. However, existing quantification methods require rather long acquisition and/or post-processing times, making implementation difficult both in research studies on healthy unsedated children and in clinical examinations. The goal of this work was to propose a novel strategy for f my quantification within acceptable acquisition and post-processing times. Our approach is based on a 3-compartment model (myelin-related water, intra/extra-cellular water and unrestricted water), and uses calibrated values of inherent relaxation times (T1 c and T2 c) for each compartment c. Calibration was first performed on adult relaxometry datasets (N = 3) acquired with large numbers of inversion times (TI) and echo times (TE), using an original combination of a region contraction approach and a non-negative least-square (NNLS) algorithm. This strategy was compared with voxel-wise fitting, and showed robust estimation of T1 c and T2 c. The accuracy of f my calculations depending on multiple factors was investigated using simulated data. In the testing stage, our strategy enabled fast f my mapping, based on relaxometry datasets acquired with reduced TI and TE numbers (acquisition

Summary Time-adaptive sensitivity encoding (TSENSE) and generalized autocalibrating partially parallel acquisition (GRAPPA) were applied to a gradient-echo sequence used for first-pass myocardial perfusion imaging of 12 patients with coronary artery disease. The two parallel imaging methods were compared in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and image artefacts. Image acquisition was started during the administration of a Gd-contrast bolus (0.1 mmoL/kg) followed by a 20-mL saline flush (3 mL/s), and the next perfusion was started at least 15 min thereafter using an identical bolus. The order of perfusion sequences was inverted in every other patient. Both acquisitions had an acceleration rate of 2, and were performed during breath-holding. The SNR, CNR and image quality of the GRAPPA images were significantly better than were those of the TSENSE images. An exception was the lower CNR of GRAPPA when applied after the second bolus. Differences between subjects were larger with GRAPPA perfusion imaging than with TSENSE. The SNR and CNR also varied relatively much between the GRAPPA images, indicating that the diagnostic value of TSENSE may be superior after all.

The fast MRI method of Skipped Phase Encoding and Edge Deghosting (SPEED) is further developed to accelerate multiple acquisitions. In a single acquisition, SPEED first acquires three sparse ghosted edge maps with an undersampling factor of N/3, which are modeled with a double-layer structure and described by three equations with two unknown ghosts, each with a unique ghost order index. By minimizing least-square-error, a pair of ghost order indexes is determined. Based on them, the two corresponding ghosts are resolved, leading to a deghosted image. In this case, three equations are needed to determine the ghost order index, while only two equations are required to resolve the two ghosts. This shows both inefficiency and potential. Multiple acquisitions often contain similar spatial information. The similarities can be used to improve efficiency by sharing the ghost order index among different acquisitions, leading to acceleration factors greater than that achievable with single acquisition. Magn Reson Med 61:229–233, 2009. © 2008 Wiley-Liss, Inc.

In many clinical MRI scenarios, existing imaging information can be used to significantly shorten acquisition time or improve Signal to Noise Ratio (SNR). In those cases, a previously acquired image can serve as a reference image, that may exhibit similarity in some sense to the image being acquired. Examples include similarity between adjacent slices in high resolution MRI, similarity between various contrasts in the same scans and similarity between different scans of the same patients. In this paper we present a general framework for utilizing reference images for fast MRI. We take into account that the reference image may exhibit low similarity with the acquired image and develop a hybrid adaptive-weighted approach for sampling and reconstruction. Experiments demonstrate the performance of the method in three different clinical MRI scenarios: SNR improvement in high resolution brain MRI, utilizing similarity between T2-weighted and fluid-attenuated inversion recovery (FLAIR) for fast FLAIR scanning and utilizing similarity between baseline and follow-up scans for fast follow-up scanning.

Introduction Screening for breast cancer in high-risk women takes about 40 minutes to acquire an MRI scan and is time-intensive to report. There is recent interest in the performance of an abbreviated MRI protocol (FAST) in the screening setting. FAST scans have a reported negative predictive value of 99.8%. This study evaluates the false positive rates (FPR) and recall rates for FAST scans as compared to full diagnostic studies (FD). Methods A database of all screening breast MRI scans performed at our institution between 30 June 2013 and 1 July 2014 (n = 591) was created by one of the researchers, who did not subsequently analyse the MRI scans. The T1W and first post-contrast and subtracted images from each of these scans (FAST protocol) were assessed by experienced breast MRI radiologists, blinded to the final diagnosis. The findings were then compared with the FD result. Results The recall rates were 6.6% for FAST scans and 5.8% for FD scans. FPR rates were 4.7% and 3.9% respectively. There is no statistically significant difference in the recall rates or FPR of FAST scans in comparison with full diagnostic studies. Conclusions Given the absence of statistically significant difference in the FPR and recall rates in comparison with FD, FAST scans can replace FD for screening of breast cancer.

PurposeTo design parallel transmit (pTx) simultaneous multislice (SMS) spokes pulses with explicit control for peak power and local and global specific absorption rate (SAR). MethodsWe design SMS pTx least-squares and magnitude least squares spokes pulses while constraining local SAR using the virtual observation points (VOPs) compression of SAR matrices. We evaluate our approach in simulations of a head (7T) and a body (3T) coil with eight channels arranged in two z-rows. ResultsFor many of our simulations, control of average power by Tikhonov regularization of the SMS pTx spokes pulse design yielded pulses that violated hardware and SAR safety limits. On the other hand, control of peak power alone yielded pulses that violated local SAR limits. Pulses optimized with control of both local SAR and peak power satisfied all constraints and therefore had the best excitation performance under limited power and SAR constraints. These results extend our previous results for single slice pTx excitations but are more pronounced because of the large power demands and SAR of SMS pulses. ConclusionsExplicit control of local SAR and peak power is required to generate optimal SMS pTx excitations satisfying both the system's hardware limits and regulatory safety limits. Magn Reson Med 73:1946-1953, 2015. (c) 2014 Wiley Periodicals, Inc.

PURPOSE Evaluation of sensitivity and false positive findings of two fast MRI sequences for the detection of pulmonary nodules in comparison with spiral CT by two independent observers. MATERIALS AND METHODS All 30 enrolled patients had a spiral CT or MSCT as base line study. MRI was performed with a 1.5 T MR scanner (Sonata, Siemens) using a transverse 3D gradient echo sequence (3D-GRE: TR/TE/flip = 2.9 ms/1.1 ms/5 degrees ) and a half-Fourier single-shot fast spin-echo sequence (HASTE: TR/TE/flip = 800/25/150 degrees ) acquired in three planes. A separate analysis for both sequences was carried out prospectively by two independent readers (A and B) with different experience regarding pulmonary MRI. Additionally, a retrospective reading with knowledge of the CT scans was done. Results were calculated for all lesions and for lesions larger than 4 mm. RESULTS The sensitivities were 73 %, 70 % and 84 % for the 3D-GRE sequence (reader A, reader B, retrospective reading) and 65 %, 68 % and 81 % for the HASTE sequence. For lesions larger than 4 mm, the sensitivities were 93 %, 89 %, 96 % for the 3D-GRE sequence and 85 %, 85 %, 96 % for the HASTE sequence. The rate of false positive findings depended on the reader's experience, but was generally lower for the 3D-GRE sequence with 2 and 16 (reader A and B) false positive nodules compared to 4 and 40 false positive findings for the HASTE sequence. The 3D-GRE sequence was more accurate for both readers (reader A: p = 0.08, reader B: p = 0.00003). CONCLUSION The sensitivity of MRI for the detection of lung nodules was only acceptable for lesions larger than 4 mm. The 3D-GRE sequence is superior to the HASTE sequence due to the reduced amount of false positive findings with comparable sensitivity.

Magnetic resonance imaging (MRI) is used to provide spatially resolved structural and chemical composition characterisation of droplets undergoing freezing. To this end, MRI is applied to a 2 mm diameter sucrose solution droplet, suspended in cold air. During the consequential solidification of the droplet, the spatial location of nucleation and the crystal growth of the droplet are followed using non-invasive two dimensional (2D) images; these are produced using the fast MRI technique, RARE. This is able to both quantify crystal growth rates, as well as the unfrozen liquid mass fraction for the optically opaque freezing droplets. Such information is of major interest in the verification of models describing the freezing of such droplets. The spatial re-distribution of the sucrose solute as a consequence of freezing is monitored using MR 1D chemical shift profiling. The formation of a concentrated sucrose layer at the droplet surface was detected.

Traditionally, the mainstay of head and neck MR imaging has been the identification of structural alterations resulting from pathology. Now, the advent of fast MR imaging techniques provides the opportunity for radiologists to integrate structural and functional imaging in the head and neck. This article highlights functional imaging techniques that provide a means toward a complete evaluation of structural integrity and function in various systems of the head and neck.

The purpose of this study is to quantitatively compare the image quality and efficiency provided by widely available fast MR imaging pulse sequences. A composite phantom with various T1 and T2 values and subjected to periodic motion was imaged at 1.5 T. The fast MRI sequences evaluated included fast spin-echo (FSE), single shot fast spin-echo (SSFSE), echo-planar imaging (EPI), multi-slice gradient recalled (MPGR), fast MPGR (FMPGR), and fast multi-slice spoiled gradient echo (FMPSPGR). T1-weighted (T1WI), T2-weighted (T2WI), proton-density-weighted (PDWI), and T2∗-weighted (T2∗WI) images were evaluated in breath-hold and non-breath-hold time frames. Analysis included measurement of image signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), nonuniformity, ghosting ratio, SNR per unit time and CNR per unit time. Among fast T2WI sequences, FSE with breath-hold time frame resulted in the highest image quality and in superior SNR and CNR efficiency by a factor of 5 or 6 as compared with conventional spin echo sequence. Among fast T1WI sequences, FMPGR and FMPSPGR both with non-breath-hold time frame produced the highest image quality and SNR and CNR efficiency by a factor of greater than 5 as compared with conventional spin echo. Among fast PDWI and T2∗WI sequences, FSE produced the highest SNR and CNR, and was maximally efficient with a factors of greater than 6 as compared with conventional spin echo.

International audience; An approach for sensitive magnetic resonance detection of metal cations is proposed. Combining the use of hyperpolarized 129Xe NMR and of a cage-molecule functionalized by a ligand able to chelate different cations, we show that simultaneous detection of lead, zinc, and cadmium ions at nanomolar concentration is possible in short time, thanks to fast MRI sequences based on the HyperCEST scheme.

This article describes the fast MRI of fetal abnormalities and placental anomalies in evaluation of the usefulness of fast MRI in obstetric diagnoses. Fast MRI provides excellent resolution for imaging fetal and maternal anatomies without the need for sedation. Fast MRI is therefore useful to clarify diagnoses suggested by equivocal ultrasonographic findings and to obtain additional information for prenatal counseling and management.

The purpose of this study was to compare the diagnostic efficacy of a newly developed T1-weighted three-dimensional segmented echo planar imaging (3D EPI) sequence versus a conventional T1-weighted three dimensional spoiled gradient echo (3D GRE) sequence in the evaluation of brain tumors. Forty-four patients with cerebral tumors and infections were examined on a 1.0 T MR unit with 23 mT/m gradient strength. The total scan time for the T1 3D EPI sequence was 2 min 12 s, and for a conventional 3D GRE sequence it was 4 min 59 s. Both sequences were performed after administration of a contrast agent. The images were analyzed by three radiologists. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, signal-to-noise and contrast-to-noise-ratio (C/N) were calculated. The gray-white differentiation and C/N ratio of 3D EPI were found to be inferior to conventional 3D GRE images, but the difference was not statistically significant. In the qualitative comparison, lesion detection and conspicuity of 3D EPI images and conventional 3D GRE images were similar, but a tow-fold reduction of the scanning time was obtained. With the 3D EPI technique, a 50% scan time reduction could be achieved with acceptable image quality compared to conventional 3D GRE. Thus, the 3D EPI technique could replace conventional 3D GRE in the preoperative imaging of brain.

MRI-guided treatment is a growing area of medicine, particularly in radiotherapy and surgery. The exquisite soft tissue anatomic contrast offered by MRI, along with functional imaging, makes the use of MRI during therapeutic procedures very attractive. Challenging the utility of MRI in the therapy room are many issues including the physics of MRI and the impact on the environment and therapeutic instruments, the impact of the room and instruments on the MRI; safety, space, design and cost. In this session, the applications and challenges of MRI-guided treatment will be described. The session format is: 1. Past, present and future: MRI-guided radiotherapy from 2005 to 2025: Jan Lagendijk 2. Battling Maxwell’s equations: Physics challenges and solutions for hybrid MRI systems: Paul Keall 3. I want it now!: Advances in MRI acquisition, reconstruction and the use of priors to enable fast anatomic and physiologic imaging to inform guidance and adaptation decisions: Yanle Hu 4. MR in the OR: The growth and applications of MRI for interventional radiology and surgery: Rebecca Fahrig Learning Objectives: 1. To understand the history and trajectory of MRI-guided radiotherapy 2. To understand the challenges of integrating MR imaging systems with linear accelerators 3. To understand the latest in fast MRI methods to enable the visualisation of anatomy and physiology on radiotherapy treatment timescales 4. To understand the growing role and challenges of MRI for image-guided surgical procedures My disclosures are publicly available and updated at: http://sydney.edu.au/medicine/radiation-physics/about-us/disclosures.php

MRI-guided treatment is a growing area of medicine, particularly in radiotherapy and surgery. The exquisite soft tissue anatomic contrast offered by MRI, along with functional imaging, makes the use of MRI during therapeutic procedures very attractive. Challenging the utility of MRI in the therapy room are many issues including the physics of MRI and the impact on the environment and therapeutic instruments, the impact of the room and instruments on the MRI; safety, space, design and cost. In this session, the applications and challenges of MRI-guided treatment will be described. The session format is: 1. Past, present and future: MRI-guided radiotherapy from 2005 to 2025: Jan Lagendijk 2. Battling Maxwell’s equations: Physics challenges and solutions for hybrid MRI systems: Paul Keall 3. I want it now!: Advances in MRI acquisition, reconstruction and the use of priors to enable fast anatomic and physiologic imaging to inform guidance and adaptation decisions: Yanle Hu 4. MR in the OR: The growth and applications of MRI for interventional radiology and surgery: Rebecca Fahrig Learning Objectives: 1. To understand the history and trajectory of MRI-guided radiotherapy 2. To understand the challenges of integrating MR imaging systems with linear accelerators 3. To understand the latest in fast MRI methods to enable the visualisation of anatomy and physiology on radiotherapy treatment timescales 4. To understand the growing role and challenges of MRI for image-guided surgical procedures My disclosures are publicly available and updated at: http://sydney.edu.au/medicine/radiation-physics/about-us/disclosures.php

MRI-guided treatment is a growing area of medicine, particularly in radiotherapy and surgery. The exquisite soft tissue anatomic contrast offered by MRI, along with functional imaging, makes the use of MRI during therapeutic procedures very attractive. Challenging the utility of MRI in the therapy room are many issues including the physics of MRI and the impact on the environment and therapeutic instruments, the impact of the room and instruments on the MRI; safety, space, design and cost. In this session, the applications and challenges of MRI-guided treatment will be described. The session format is: 1. Past, present and future: MRI-guided radiotherapy from 2005 to 2025: Jan Lagendijk 2. Battling Maxwell’s equations: Physics challenges and solutions for hybrid MRI systems: Paul Keall 3. I want it now!: Advances in MRI acquisition, reconstruction and the use of priors to enable fast anatomic and physiologic imaging to inform guidance and adaptation decisions: Yanle Hu 4. MR in the OR: The growth and applications of MRI for interventional radiology and surgery: Rebecca Fahrig Learning Objectives: 1. To understand the history and trajectory of MRI-guided radiotherapy 2. To understand the challenges of integrating MR imaging systems with linear accelerators 3. To understand the latest in fast MRI methods to enable the visualisation of anatomy and physiology on radiotherapy treatment timescales 4. To understand the growing role and challenges of MRI for image-guided surgical procedures My disclosures are publicly available and updated at: http://sydney.edu.au/medicine/radiation-physics/about-us/disclosures.php

MRI-guided treatment is a growing area of medicine, particularly in radiotherapy and surgery. The exquisite soft tissue anatomic contrast offered by MRI, along with functional imaging, makes the use of MRI during therapeutic procedures very attractive. Challenging the utility of MRI in the therapy room are many issues including the physics of MRI and the impact on the environment and therapeutic instruments, the impact of the room and instruments on the MRI; safety, space, design and cost. In this session, the applications and challenges of MRI-guided treatment will be described. The session format is: 1. Past, present and future: MRI-guided radiotherapy from 2005 to 2025: Jan Lagendijk 2. Battling Maxwell’s equations: Physics challenges and solutions for hybrid MRI systems: Paul Keall 3. I want it now!: Advances in MRI acquisition, reconstruction and the use of priors to enable fast anatomic and physiologic imaging to inform guidance and adaptation decisions: Yanle Hu 4. MR in the OR: The growth and applications of MRI for interventional radiology and surgery: Rebecca Fahrig Learning Objectives: 1. To understand the history and trajectory of MRI-guided radiotherapy 2. To understand the challenges of integrating MR imaging systems with linear accelerators 3. To understand the latest in fast MRI methods to enable the visualisation of anatomy and physiology on radiotherapy treatment timescales 4. To understand the growing role and challenges of MRI for image-guided surgical procedures My disclosures are publicly available and updated at: http://sydney.edu.au/medicine/radiation-physics/about-us/disclosures.php

MRI-guided treatment is a growing area of medicine, particularly in radiotherapy and surgery. The exquisite soft tissue anatomic contrast offered by MRI, along with functional imaging, makes the use of MRI during therapeutic procedures very attractive. Challenging the utility of MRI in the therapy room are many issues including the physics of MRI and the impact on the environment and therapeutic instruments, the impact of the room and instruments on the MRI; safety, space, design and cost. In this session, the applications and challenges of MRI-guided treatment will be described. The session format is: 1. Past, present and future: MRI-guided radiotherapy from 2005 to 2025: Jan Lagendijk 2. Battling Maxwell’s equations: Physics challenges and solutions for hybrid MRI systems: Paul Keall 3. I want it now!: Advances in MRI acquisition, reconstruction and the use of priors to enable fast anatomic and physiologic imaging to inform guidance and adaptation decisions: Yanle Hu 4. MR in the OR: The growth and applications of MRI for interventional radiology and surgery: Rebecca Fahrig Learning Objectives: 1. To understand the history and trajectory of MRI-guided radiotherapy 2. To understand the challenges of integrating MR imaging systems with linear accelerators 3. To understand the latest in fast MRI methods to enable the visualisation of anatomy and physiology on radiotherapy treatment timescales 4. To understand the growing role and challenges of MRI for image-guided surgical procedures My disclosures are publicly available and updated at: http://sydney.edu.au/medicine/radiation-physics/about-us/disclosures.php

A modified spiral imaging technique is presented, in which the conventional sinusoidal gradient waveforms are replaced by trapezoidal ones. In addition to allowing a reduced data acquisition time, the new waveforms circumvent specific hardware restrictions on the minimum scan repetition time.

Background The aim of this study is to investigate the outcomes of magnetic resonance imaging (MRI)–based individual thrombolysis therapy using recombinant tissue plasminogen activator (rt-PA) in patients with superacute infarction, comparing the outcome in 1 group of patients treated within 4.5 hours compared with 4.5- to 12-hour window treatment group. Methods We studied 135 patients stratified to 2 different groups based on whether they presented with stroke symptoms within 4.5 hours (4.5-hour group, 72 patients) or between 4.5 and 12 hours (4.5- to 12-h group, 63 patients). All patients were treated with rt-PA after MRI confirmed superacute ischemic stroke (hyperintense in diffusion-weighted imaging but no hypointense change in T2-weighted image (T2WI) or fluid-attenuated inversion recovery). Clinical neurologic deficit was evaluated using the National Institutes of Health Stroke Scale on admission, at 24 hours, and 7 days later. A 90-day clinical outcome was assessed using the modified Rankin Scale (mRS). Results There was no significant difference in the clinical outcome between the patients treated with thrombolysis within the first 4.5 hours and those treated between 4.5 and 12 hours. The 2 groups both had recanalization, mRS, and favorable outcome at 90 days (P > .05). Conclusions Our study suggested that fast MR-based thrombolysis using rt-PA was safe and reliable in superacute infarction within 4.5 hours and 4.5-12 hours poststroke.

15 patients, aged 1-14 years, with sleep disordered breathing underwent turbo fast low angle shot MRI during drug-induced sleep. The site of obstruction within the pharynx was identified. Data from MRI were compared with fibroscopic findings. The degree of hypertrophy of the palatine tonsils as determined by MRI was also compared with that determined by visual inspection while awake. MRI was completed in all cases, whereas fibroscopy was completed in only six of the 10 cases examined. MRI findings agreed with those of fibroscopy in all the patients who underwent both investigations. On MRI, the pharynx was obstructed in 12 of the 15 cases examined (80%); the palatine tonsils were involved in all of these while both the palatine tonsils and nasopharynx were obstructed in three of the 12 cases. One of the 12 patients was graded as Grade I of Mackenzie's scale. One of the cases graded as Grade II showed no obstruction. In conclusion, fast MRI proved useful in identifying the site of pharyngeal obstruction in young patients with sleep disordered breathing.

Purpose: We present a case of a 4-year-old child who was incidentally found to have a suprasellar arachnoid cyst (SAC) after initial CT imaging at 6 weeks of age but who demonstrated no anomalies. This is only the sixth case of intracranial de novo ACs documented in the English literature and only the second case of SAC to arise de novo. Methods: Case review after an SAC was found on an MRI scan at 4 years of age which had not been present on a previous CT of the head. Results: Apparent de novo SAC formation in a healthy 4-year-old female without a history of intracranial infection, surgery or trauma. Conclusion: The pathophysiology leading to the formation of the cyst might well be congenital, although there is some question as to how early in development the cysts are formed as our child was a 32-week GA preemie with an initial scan at 38 weeks GA. With the use of fast MRI scans instead of CT scans and the continued neuroimaging of premature infants, we can take a better look at the anatomy and better determine the timing of development of the SAC.

Compressive sensing (CS) is an emerging technique for fast MRI, which relies on the sparsity constraint of the underlying image to reduce the data acquisition requirement. Sparsifying transforms, such as total variation (TV), wavelet, curvelet, have been used in CS-MRI as regularization terms. Linear weighted summations of these regularization terms have also been used and tested. However, tuning the weights for individual terms is complicated and time-consuming. In this paper, a novel method that uses combined sparsifying transforms is proposed. This method applies transforms sequentially. It can avoid the artifacts associated with a single transform, as well as save the time of tuning the weights. Simulated results using in-vivo data show that the proposed method is efficient while providing similar or improved reconstruction quality.

The ultrafast magnetic resonance imaging technique known as echo-planar imaging has undergone considerable technical improvements in recent years. It is currently being evaluated at only a few institutions worldwide. Although EPI, invented by P. Mansfield in 1977, is the oldest fast MRI technique, it is still not widely available on clinical scanners. Only 20–30 EPI scanners exist worldwide, compared to about 7000 conventional MRI scanners. The main reason why EPI has not emerged from the scientific prototype niche is its high demands on hardware and software. However, the time is now coming when EPI is entering the clinical stage. We describe the common EPI sequence types, show clinical results, and describe the contrast in the measured images.

We present a fast MRI technique sensitized to microscopic susceptibility effects. The method combines elements of echo-shifted gradient-recalled MR imaging (TE > TR) with the acquisition of multiple k-space lines within a single TR-period. The sequence results in a much reduced imaging time as compared with conventional gradient-echo MRI methods. The feasibility of the method is demonstrated for susceptibility bolus tracking in the cat brain using an imaging time of 153 ms. The relative cerebral blood volume maps created with this method are comparable with those obtained with conventional methods.

The principles of a fast T2*-sensitized MR imaging method (Moonen et al., Magn. Reson. Med. 26, 184 (1992)) are extended to further increase T2* sensitivity. It is shown that the period of T2*-weighting can be lengthened by n TR-periods by appropriate gradient schemes without RF refocusing resulting in progressively delayed gradient-recalled echoes. This extension of the echo-shifting concept thus introduces large flexibility in the choice of T2*-weighting without changing total imaging time. The coherence pathway formalism is used to evaluate and describe the selection of the desired echo and the attenuation of unwanted coherences. The new techniques are demonstrated for tracking a bolus of susceptibility contrast agent in cat brain. Relative blood-volume maps are derived with expected contrast between white and gray matter.

Improvements in crossed images are presented by application of snapshot FLASH MRImaging which reduces the imaging time in localizedin vivo NMR spectroscopy. The method enables correlation of the volume of interest with its surroundings and determines the set of offset frequencies of the selective RF pulses to locate the volume of interest.

Excised mice kidney, heart and skin MRI visible features were quantitated using ex vivo 21 Tesla MRI microimager. The fast MRI acquisition protocols of FLASH, gradient echo flow compensated (GEFC) techniques were used to visualize microvasculature of mice kidney, mice heart including cardiac arteries, veins, cordate tendons and mice skin epidermis with hair follicle features.

In this work a theoretical description for practical quantitative estimation of the noise enhancement in generalized autocalibrating partially parallel acquisitions (GRAPPA) reconstructions, equivalent to the geometry (g)-factor in sensitivity encoding for fast MRI (SENSE) reconstructions, is described. The GRAPPA g-factor is derived directly from the GRAPPA reconstruction weights. The procedure presented here also allows the calculation of quantitative g-factor maps for both the uncombined and combined accelerated GRAPPA images. This enables, for example, a fast comparison between the performances of various GRAPPA reconstruction kernels or SENSE reconstructions. The applicability of this approach is validated on phantom studies and demonstrated using in vivo images for 1D and 2D parallel imaging. Magn Reson Med 62: 739 –746, 2009. © 2009 Wiley-Liss, Inc.

A fast multi-section MR imaging technique is described. Gradient- and spin-echo (GRASE) imaging utilizes the speed advantages of gradient refocusing while overcoming the image artifacts arising from static field inhomogeneity and chemical shift. Image contrast is determined by the T2 contrast in the Hahn spin echoes. A novel k-space trajectory temporally modulates signals and demodulates artifacts.

The aim of this study was to evaluate reproducibility of a fast MRI protocol to measure gastric emptying and motility of the gastric antrum.Gastric emptying and antral speed were measured in 12 type 1 diabetic patients (mean age 43 years) and 9 healthy volunteers (mean age 31 years). Subjects, fasting from 6h, were evaluated in supine position using a 1.5T MR scanner and a eight-channels phased-array body coil after ingestion of 400 ml of a vanillas pudding mixed with 5 ml of Gd-DTPA. Axial 3D T1w sequence at 0 and 30 min for volume evaluation and cine-steady state acquisition every 5 min for a total time of 30 min for gastric wave speed assessing were acquired. Two blinded observers extrapolated T(1/2) from gastric volume assessment and speed of gastric waves.All the patients tolerated the examination. The T(1/2) cut-off was of 115 min with an accuracy in differentiate controls from diabetics of 96% (95% CI 0.766-0.992; p0.001), while the antral speed cut-off was of 0.15 mm/s with an accuracy of 87% (95% CI 0.628-0.977; p0.001). The inter-observer agreement for the volumes at time 0 and 30 min was respectively 0.983 (95% CI 0.9628-0.9929; p0.001) and 0.9933 (95% CI 0.9847-0.9971; p0.001) with an agreement of 0.9918 (95% CI 0.9853-0.9954; p0.001), while for antral speed it was of 0.935 (95% CI 0.9097-0.9528; p0.001).MRI is a reproducible technique for the evaluation of gastric emptying and antral motility.

International audience; Real-time cardiac MRI appears as a promising technique to evaluate the mechanical function of the heart. However, ultra-fast MRI acquisitions come with an important signal-to-noise ratio (SNR) penalty, which drastically reduces the image quality. Hence, a real-time denoising approach would be desirable for SNR amelioration. In the clinical context of cardiac dysfunction assessment, long acquisitions are required and for most patients the acquisition takes place with free breathing. Hence, it is necessary to compensate respiratory motion in real-time. In this article, a real-time and interactive method for sequential registration and denoising of real-time MR cardiac images is presented. The method has been experimented on 60 fast MRI acquisitions in five healthy volunteers and five patients. These experiments assessed the feasibility of the method in a real-time context.

Clinical use of cardiac synchronized Magnetic Resonance Imaging has been limited because of long unacceptable acquisition times. BRISK (Block Regional Interpolation Scheme for k-space) is a rapid MRI technique, which employs temporal sparse sampling scheme that varies the sampling rate as a function of distance from the k-space center. Using combination of conventional segmentation and BRISK approach, a new rapid phase contrast cine approach named FAST was investigated. FAST technique samples contiguous regions of k-space using a segmentation factor, just as in conventional segmentation, with the difference that the segmentation factor (SF) is varied as a function of distance from the k-space center. FAST and BRISK can be performed in nearly equally scan times. Both retained excellent axial-velocity accuracy. However secondary velocities, which were two orders of magnitude lower than the primary, suffered from comparable inaccuracies and distortion in conventional segmentation, BRISK and FAST.Copyright © 2004 by ASME