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Purpose: To develop and test compressed sensing–based multiframe 3D MRI of grid‐tagged hyperpolarized gas in the lung. Theory and Methods: Applying grid‐tagging RF pulses to inhaled hyperpolarized gas results in images in which signal intensity is predictably and sparsely distributed. In the present work, this phenomenon was used to produce a sampling pattern in which k‐space is undersampled by a factor of approximately seven, yet regions of high k‐space energy remain densely sampled. Three healthy subjects received multiframe 3D 3He tagging MRI using this undersampling method. Images were collected during a single exhalation at eight timepoints spanning the breathing cycle from end‐of‐inhalation to end‐of‐exhalation. Grid‐tagged images were used to generate 3D displacement maps of the lung during exhalation, and time‐resolved maps of principal strains and fractional volume change were generated from these displacement maps using finite‐element analysis. Results: Tags remained clearly resolvable for 4–6 timepoints (5–8 s) in each subject. Displacement maps revealed noteworthy temporal and spatial nonlinearities in lung motion during exhalation. Compressive normal strains occurred along all three principal directions but were primarily oriented in the head–foot direction. Fractional volume changes displayed clear bilateral symmetry, but with the lower lobes displaying slightly higher change than the upper lobes in 2 of the 3 subjects. Conclusion: We developed a compressed sensing–based method for multiframe 3D MRI of grid‐tagged hyperpolarized gas in the lung during exhalation. This method successfully overcomes previous challenges for 3D dynamic grid‐tagging, allowing time‐resolved biomechanical readouts of lung function to be generated. [ABSTRACT FROM AUTHOR]

Inhaled hyperpolarized helium-3 ([sup.3]He) gas is a new magnetic resonance (MR) contrast agent that is being used to study lung functionality. To evaluate the total lung ventilation from the hyperpolarized [sup.3]He MR images, it is necessary to segment the lung cavities. This is difficult to accomplish using only the hyperpolarized [sup.3]He MR images, so traditional proton ([sup.1]H) MR images are frequently obtained concurrent with the hyperpolarized [sup.3]He MR examination. Segmentation of the lung cavities from traditional proton ([sup.1]H) MRI is a necessary first step in the analysis of hyperpolarized [sup.3]He MR images. In this paper, we develop an active contour model that provides a smooth boundary and accurately captures the high curvature features of the lung cavities from the [sup.1]H MR images. This segmentation method is the first parametric active contour model that facilitates straightforward merging of multiple contours. The proposed method of merging computes an external force field that is based on the solution of partial differential equations with boundary condition defined by the initial positions of the evolving contours. A theoretical connection with fluid flow in porous media and the proposed force field is established. Then by using the properties of fluid flow we prove that the proposed method indeed achieves merging and the contours stop at the object boundary as well. Experimental results involving merging in synthetic images are provided. The segmentation technique has been employed in lung [sup.1]H MR imaging for segmenting the total lung air space. This technology plays a key role in computing the functional air space from MR images that use hyperpolarized [sup.3]He gas as a contrast agent. Index Terms--Active contour, hyperpolarized gas MRI, image segmentation, merging.

Purpose To evaluate T2 [ABSTRACT FROM AUTHOR]

Purpose: To evaluate regional anisotropy of lung-airspace orientation by assessing the dependence of helium-3 ((3) He) apparent diffusion coefficient (ADC) values on the direction of diffusion sensitization at two field strengths.Materials and Methods: Hyperpolarized (3) He diffusion-weighted magnetic resonance imaging (MRI) of the lung was performed at 0.43T and 1.5T in 12 healthy volunteers. A gradient-echo pulse sequence was used with a bipolar diffusion-sensitization gradient applied separately along three orthogonal directions. ADC maps, median ADC values, and signal-to-noise ratios were calculated from the diffusion-weighted images. Two readers scored the ADC maps for increased values at lung margins, major fissures, or within focal central regions.Results: ADC values were found to depend on the direction of diffusion sensitization (P < 0.01, except for craniocaudal vs. anteroposterior directions at 1.5T) and were increased at the lateral and medial surfaces for left-right diffusion sensitization (12 of 12 subjects); at the apex and base (9 of 12), and along the major fissure (8 of 12), for craniocaudal diffusion sensitization; and at the most anterior and posterior lung (10 of 12) for anteroposterior diffusion sensitization. Median ADC values at 0.43T (0.201 ± 0.017, left-right; 0.193 ± 0.019, craniocaudal; and 0.187 ± 0.017 cm(2) /s, anteroposterior) were slightly lower than those at 1.5T (0.205 ± 0.017, 0.197 ± 0.017 and 0.194 ± 0.016 cm(2) /s, respectively; P < 0.05).Conclusion: These findings indicate that diffusion-weighted hyperpolarized (3) He MRI can detect regional anisotropy of lung-airspace orientation, including that associated with preferential orientation of terminal airways near pleural surfaces. [ABSTRACT FROM AUTHOR]

Purpose: We aimed to evaluate the safety and efficacy of fluoroscopically placed jejunal extension tubes (J-arm) in patients with existing gastrostomy tubes. Methods: We conducted a retrospective review of 391 J-arm placements performed in 174 patients. Indications for jejunal nutrition were aspiration risk (35%), pancreatitis (17%), gastroparesis (13%), gastric outlet obstruction (12%), and other (23%). Technical success, complications, malfunctions, and patency were assessed. Percutaneous gastrostomy (PEG) tube location, J-arm course, and fluoroscopy time were correlated with success/failure. Failure was defined as inability to exit the stomach. Procedure-related complications were defined as adverse events related to tube placement occurring within seven days. Tube malfunctions and aspiration events were recorded and assessed. Results: Technical success was achieved in 91.9% (95% CI, 86.7%-95.2%) of new tubes versus 94.2% (95% CI, 86.7%-95.2%) of replacements (P = 0.373). Periprocedural complications occurred in three patients (0.8%). Malfunctions occurred in 197 patients (50%). Median tube patency was 103 days (95% CI, 71-134 days). No association was found between successful J-arm placement and gastric PEG tube position (P = 0.677), indication for jejunal nutrition (P = 0.349), J-arm trajectory in the stomach and incidence of malfunction (P = 0.365), risk of tube migration and PEG tube position (P = 0.173), or J-arm length (P = 0.987). A fluoroscopy time of 21.3 min was identified as a threshold for failure. Malfunctions occurred more often in tubes replaced after 90 days than in tubes replaced before 90 days (P < 0.001). A total of 42 aspiration events occurred (OR 6.4, P < 0.001, compared with nonmalfunctioning tubes). Conclusion: Fluoroscopy-guided J-arm placement is safe for patients requiring jejunal nutrition. Tubes indwelling for longer than 90 days have higher rates of malfunction and aspiration. [ABSTRACT FROM AUTHOR]

IgG4-associated cholangitis can mimic hilar cholangiocarcinoma. Previously reported patients with IgG4-associated cholangitis mimicking cholangiocarcinoma had elevated serum IgG4 levels and long-segment biliary strictures. However, in the absence of other diagnostic criteria for malignancy, IgG4-associated cholangitis should remain a consideration among patients with normal serum IgG4 and a hilar mass suspicious for cholangiocarcinoma. The presence of a hilar mass and a malignant-appearing biliary stricture in two patients with normal serum IgG4 prompted further evaluation and subsequent concomitant liver and bile duct resection and reconstruction. The diagnosis of IgG4-associated cholangitis was established during the pathologic evaluation of the resected specimens. IgG4-associated cholangitis is a known imitator of hilar cholangiocarcinoma and should be considered in the differential diagnosis even among serologically IgG4-negative patients with a hilar mass prior to operative resection. [ABSTRACT FROM AUTHOR]

Purpose: To develop an automated segmentation method to differentiate the ventilated lung volume on 3He magnetic resonance imaging (MRI). Materials and Methods: Computational processing (CP) for each subject consisted of the following three essential steps: 1) inhomogeneity bias correction, 2) whole lung segmentation, and 3) subdivision of the lung segmentation into regions of similar ventilation. Evaluation consisted of two comparative analyses: i) comparison of the number of defects scored by two human readers in 43 subjects, and ii) simultaneous truth and performance level estimation (STAPLE) in 18 subjects in which the ventilation defects were manually segmented by four human readers. Results: There was excellent correlation between the number of ventilation defects tabulated by CP and reader #1 (intraclass correlation coefficient [ICC] = 0.86), CP and reader #2 (ICC = 0.85), and between the two readers (ICC = 0.97). The STAPLE results from the second analysis yielded the following sensitivity/specificity numbers: CP (0.898/0.905), radiologist #1 (0.743/0.897), radiologist #2 (0.501/0.985), radiologist #3 (0.898/0.848), and the first author (0.600/0.984). Conclusion: We developed and evaluated an automated method for quantifying the ventilated lung volume on 3He MRI. The findings strongly indicate that our proposed algorithmic processing may be a reliable, automatic method for quantitating ventilation defects. J. Magn. Reson. Imaging 2011;. © 2011 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

A pulse-sequence strategy was developed for generating regional maps of alveolar oxygen partial pressure ( pO2) in a single 6-sec breath hold, for use in human subjects with impaired lung function. Like previously described methods, pO2 values are obtained by measuring the oxygen-induced T1 relaxation of inhaled hyperpolarized 3He. Unlike other methods, only two 3He images are acquired: one with reverse-centric and the other with centric phase-encoding order. This phase-encoding arrangement minimizes the effects of regional flip-angle variations, so that an accurate map of instantaneous pO2 can be calculated from two images acquired a few seconds apart. By combining this phase-encoding strategy with variable flip angles, the vast majority of the hyperpolarized magnetization goes directly into the T1 measurement, minimizing noise in the resulting pO2 map. The short-breath-hold pulse sequence was tested in phantoms containing known O2 concentrations. The mean difference between measured and prepared pO2 values was 1 mm Hg. The method was also tested in four healthy volunteers and three lung-transplant patients. Maps of healthy subjects were largely uniform, whereas focal regions of abnormal pO2 were observed in diseased subjects. Mean pO2 values varied with inhaled O2 concentration. Mean pO2 was consistent with normal steady-state values in subjects who inhaled 3He diluted only with room air. Magn Reson Med 63:127-136, 2010. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Purpose To investigate short- and long-time-scale 3He diffusion in asthma. Materials and Methods A hybrid MRI sequence was developed to obtain coregistered short- and long-time-scale apparent diffusion coefficient (ADC) maps during a single breath-hold. The study groups were: asthma ( n = 14); healthy ( n = 14); chronic obstructive pulmonary disease (COPD) ( n = 9). Correlations were made between mean-ADC and %ADC-abn (abnormal) (%pixels with ADC > mean +2 SD of healthy) at both time scales and spirometry. Sensitivities were determined using receiver operating characteristic (ROC) analysis. Results For asthmatics, the short- and long-time-scale group-mean ADCs were 0.254 ± 0.032 cm2/s and 0.0237 ± 0.0055 cm2/s, respectively, representing a 9% and 27% ( P = 0.038 and P = 0.005) increase compared to the healthy group. The group-mean %ADC-abn were 6.4% ± 3.7% and 17.5% ± 14.2%, representing a 107% and 272% ( P = 0.004 and P = 0.006) increase. For COPD much greater elevations were observed. %ADC-abn provided better discrimination than mean-ADC between asthmatic and healthy subjects. In asthmatics ADC did not correlate with spirometry. Conclusion With long-time scale 3He diffusion magnetic resonance imaging (MRI) changes in lung microstructure were detected in asthma that more conspicuous regionally than at the short time scale. The hybrid diffusion method is a novel means of identifying small airway disease. J. Magn. Reson. Imaging 2008;28:80-88. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]