Hing Chiu Chang

A robust multi-shot scan strategy for high-resolution diffusion weighted MRI enabled by multiplexed sensitivity-encoding (MUSE)

Diffusion weighted magnetic resonance imaging (DWI) data have been mostly acquired with single-shot echo-planar imaging (EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in single-shot EPI, even when the parallel imaging (usually at an acceleration factor of 2) is incorporated. Multi-shot acquisition strategies could potentially achieve higher spatial resolution and fidelity, but they are generally susceptible to motion-induced phase errors among excitations that are exacerbated by diffusion sensitizing gradients, rendering the reconstructed images unusable. It has been shown that shot-to-shot phase variations may be corrected using navigator echoes, but at the cost of imaging throughput. To address these challenges, a novel and robust multi-shot DWI technique, termed multiplexed sensitivity-encoding (MUSE), is developed here to reliably and inherently correct nonlinear shot-to-shot phase variations without the use of navigator echoes. The performance of the MUSE technique is confirmed experimentally in healthy adult volunteers on 3Tesla MRI systems. This newly developed technique should prove highly valuable for mapping brain structures and connectivities at high spatial resolution for neuroscience studies.

Salivary Glands: Echo-Planar versus PROPELLER Diffusion-weighted MR Imaging for Assessment of ADCs

PURPOSEnTo compare the image distortion and the quantification variation in parotid gland apparent diffusion coefficients (ADCs) on periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) versus echo-planar diffusion-weighted (DW) magnetic resonance (MR) images and to investigate the relationship between parotid gland ADC and parotid gland fat content.nnnMATERIALS AND METHODSnThis prospective study was approved by a local institutional review board. Written informed consent was obtained from all 33 enrolled healthy volunteers (15 men, 18 women; mean age, 36.4 years +/- 11.8 [standard deviation]). All participants underwent 1.5-T non-fat-saturated and fat-saturated PROPELLER DW MR imaging as well as 1.5-T nonaccelerated and twofold-accelerated echo-planar DW MR imaging. Image distortion on the DW images was qualitatively scored, and parotid ADC was quantitatively analyzed. The correlation between parotid ADC and parotid fat content was evaluated by using linear regression analysis. Wilcoxon signed rank and t tests were used for statistical analysis, with Bonferroni correction applied for multiple comparisons.nnnRESULTSnEcho-planar DW images showed distortion, which was completely eliminated on the PROPELLER DW images. The mean parotid ADCs measured with non-fat-saturated PROPELLER (0.670 x 10(-3) mm(2) +/- 0.149), nonaccelerated echo-planar (0.892 x 10(-3) mm(2) +/- 0.128), twofold-accelerated echo-planar (1.088 x 10(-3) mm(2) +/- 0.124), and fat-saturated PROPELLER (1.307 x 10(-3) mm(2) +/- 0.217) DW imaging differed significantly from one another (P < .001 for all comparisons). Parotid ADC had a significant negative correlation with parotid fat content (x) measured at non-fat-saturated PROPELLER DW imaging: ADC = -0.0087x + 1.1173 (r = 0.80, P < .001).nnnCONCLUSIONnPROPELLER DW imaging pulse sequences can yield distortion-free images for parotid ADC measurements and enable quantitative evaluation of the relationship between parotid ADC and parotid fat content.nnnSUPPLEMENTAL MATERIALnhttp://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.2531082228/-/DC1.

Effects of gender, age, and body mass index on fat contents and apparent diffusion coefficients in healthy parotid glands: an MRI evaluation.

ObjectivesTo establish standard apparent diffusion coefficient (ADC) and the fat content as a function of age, gender and body mass index (BMI) in healthy parotid glands, and to address the influences of fat suppression on ADC measurements.MethodsA total of 100 healthy adults (gender and age evenly distributed) were prospectively recruited, with parotid fat content measured from gradient-echo images with fat–water separated using iterative decomposition with echo asymmetry and least squares (IDEAL). The ADCs were estimated using both fat-saturated and non-fat-saturated diffusion-weighted imaging via a periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique.ResultsParotid fat content was larger in men than in women by about 10 percentage points (Pu2009<u20090.005), and positively associated with BMI and age for both genders (mostly with Pu2009<u20090.001). ADCs estimated with non-fat-saturated PROPELLER were significantly lower in men than in women (Pu2009<u20090.005), but showed no gender difference if measured using fat-saturated PROPELLER (Pu2009=u20090.840). The negative association between parotid ADC and age/BMI/fat (Pu2009<u20090.001) showed greater regression slopes in non-fat-saturated PROPELLER than in fat-saturated data.ConclusionsParotid fat content in healthy adults correlates positively with both age and BMI; the correlation with age is gender-dependent. Parotid ADC measurements are strongly influenced by fat saturation.Key Points• Parotid fat content in healthy adults correlates positively with age and BMI.• The rate of aging-related increase in fat contents is gender-dependent.• Parotid ADC measurements are strongly influenced by fat saturation.

Parotid Fat Contents in Healthy Subjects Evaluated with Iterative Decomposition with Echo Asymmetry and Least Squares Fat-Water Separation

PURPOSEnTo evaluate the effectiveness of three fat measurement methods for parotid glands in healthy subjects, with or without metallic dental implants.nnnMATERIALS AND METHODSnThe institutional review board approved this study, with informed consent obtained from 114 volunteers undergoing magnetic resonance (MR) imaging at 1.5 T. Fat-saturated (FS) and non-fat-saturated (NFS) fast spin-echo T1-weighted imaging (T1 method), FS and NFS T2-weighted periodically rotated overlapping parallel lines with enhanced reconstruction fast spin-echo imaging (T2 method), and gradient-echo imaging with fat-water separation using iterative decomposition with echo asymmetry and least squares (IDEAL) method were used to derive parotid fat contents. Two raters examined the homogeneity of fat saturation to determine whether parotid fat quantification was successful, with the success rate in the 114 subjects recorded for each protocol. In subjects whose fat quantification was successful with all three imaging methods, linear regression was used to analyze the correlation between any pair of the three parotid fat content measurement methods.nnnRESULTSnSuccess rates in parotid fat measurements by using T1, T2, and IDEAL methods were 87.7% (100 of 114), 87.7% (100 of 114), and 100% (114 of 114), respectively. The means of measured parotid fat contents revealed significant differences (P < .001) between any pair of the three measurement methods. The parotid fat contents measured with the three methods were significantly correlated with each other between any pair of combinations.nnnCONCLUSIONnThe IDEAL method provided a high success rate for parotid fat measurements, even in subjects with metallic dental implants.

Parotid perfusion in nasopharyngeal carcinoma patients in early-to-intermediate stage after low-dose intensity-modulated radiotherapy: Evaluated by fat-saturated dynamic contrast-enhanced magnetic resonance imaging

PURPOSEnTo investigate parotid perfusion in early-to-intermediate stage after parotid-sparing radiation dose using fat-saturated DCE-MRI, and to verify whether the perfusion alteration was related to radiation dose and the PSV.nnnMETHODS AND MATERIALSnThirty-two parotid glands from 16 consecutive patients with pathologically proven nasopharyngeal carcinoma treated by IMRT were examined. The parotid glands received a radiation dose of 28.9±3.9Gy with a PSV of 43.1%±13.9%. Perfusion parameters were calculated using time-shifted Brix model from fat-saturated DCE-MRI data before (pre-RT) and in early-to-intermediate stage after (post-RT) IMRT. Paired t-test was used to evaluate perfusion changes, while Pearsons correlation test was used to examine perfusion dependency on radiation dose and PSV. For multiple comparisons Bonferroni correction was applied.nnnRESULTSnSuccessful fat saturation was achieved in 29 of 32 parotid glands. Compared with pre-RT, the post-RT parotid glands showed significantly higher A, peak enhancement, and wash-in slope, plus a lower Kel, suggesting a mixed effect of increased vascular permeability and acinar loss. Linear regression showed that peak enhancement was positively associated with radiation dose in post-RT parotid glands. Kel and slope were negatively associated with PSV, while time-to-peak was positively associated with PSV significantly.nnnCONCLUSIONSnOur results suggest that time-shifted Brix model is feasible for quantifying parotid perfusion using DCE-MRI. The perfusion alterations in early-to-intermediate stage after IMRT might be related to a mixed effect of increased vascular permeability and acinar loss with dose and PSV dependencies.

Q-ball imaging with PROPELLER EPI acquisition.

Q‐ball imaging (QBI) is an imaging technique that is capable of resolving intravoxel fiber crossings; however, the signal readout based on echo‐planar imaging (EPI) introduces geometric distortions in the presence of susceptibility gradients. This study proposes an imaging technique that reduces susceptibility distortions in QBI by short‐axis PROPELLER EPI acquisition. Conventional QBI and PROPELLER QBI data were acquired from two 3T MR scans of the brains of five healthy subjects. Prior to the PROPELLER reconstruction, residual distortions in single‐blade low‐resolution b0 and diffusion‐weighted images (DWIs) were minimized by linear affine and nonlinear diffeomorphic demon registrations. Subsequently, the PROPELLER keyhole reconstruction was applied to the corrected DWIs to obtain high‐resolution PROPELLER DWIs. The generalized fractional anisotropy and orientation distribution function maps contained fewer distortions in PROPELLER QBI than in conventional QBI, and the fiber tracts more closely matched the brain anatomy depicted by turbo spin‐echo (TSE) T2‐weighted imaging (T2WI). Furthermore, for fixed TE, PROPELLER QBI enabled a shorter scan time than conventional QBI. We conclude that PROPELLER QBI can reduce susceptibility distortions without lengthening the acquisition time and is suitable for tracing neuronal fiber tracts in the human brain. Copyright

Multilayer appearance on contrast-enhanced susceptibility-weighted images on patients with brain abscesses: Possible origins and effects of postprocessing

To demonstrate the presence of a multilayer appearance of the capsule on contrast‐enhanced (CE) susceptibility‐weighted imaging (SWI) in patients with pyogenic brain abscesses. Possible origins for the appearance and effects of postprocessing settings are discussed.

A single-shot T2 mapping protocol based on echo-split gradient-spin-echo acquisition and parametric multiplexed sensitivity encoding based on projection onto convex sets reconstruction

To develop a high‐speed T2 mapping protocol that is capable of accurately measuring T2 relaxation time constants from a single‐shot acquisition.

Free-breathing black-blood CINE fast-spin echo imaging for measuring abdominal aortic wall distensibility: A feasibility study

The paper reports a free-breathing black-blood CINE fast-spin echo (FSE) technique for measuring abdominal aortic wall motion. The free-breathing CINE FSE includes the following MR techniques: (1) variable-density sampling with fast iterative reconstruction; (2) inner-volume imaging; and (3) a blood-suppression preparation pulse. The proposed technique was evaluated in eight healthy subjects. The inner-volume imaging significantly reduced the intraluminal artifacts of respiratory motion (pu2009u2009=u2009u20090.015). The quantitative measurements were a diameter of 16.3u2009u2009±u2009u20092.8u2009mm and wall distensibility of 2.0u2009u2009±u2009u20090.4u2009mm (12.5u2009u2009±u2009u20093.4%) and 0.7u2009u2009±u2009u20090.3u2009mm (4.1u2009u2009±u2009u20091.0%) for the anterior and posterior walls, respectively. The cyclic cross-sectional distensibility was 35u2009u2009±u2009u200915% greater in the systolic phase than in the diastolic phase. In conclusion, we developed a feasible CINE FSE method to measure the motion of the abdominal aortic wall, which will enable clinical scientists to study the elasticity of the abdominal aorta.

Efficient imaging of midbrain nuclei using inverse double-echo steady-state acquisition

PURPOSEnImaging of midbrain nuclei using T2- or T2*-weighted MRI often entails long echo time, leading to long scan time. In this study, an inverse double-echo steady-state (iDESS) technique is proposed for efficiently depicting midbrain nuclei.nnnMETHODSnThirteen healthy subjects participated in this study. iDESS was performed along with two sets of T2*-weighted spoiled gradient-echo images (SPGR1, with scan time identical to iDESS and SPGR2, using clinical scanning parameters as a reference standard) for comparison. Generation of iDESS composite images combining two echo signals was optimized for maximal contrast-to-noise ratio (CNR) between the red nuclei and surrounding tissues. Signal-to-noise ratios (SNRs) were calculated from the occipital lobe. Comparison was also made using phase-enhanced images as in standard susceptibility-weighted imaging (SWI).nnnRESULTSnThe iDESS images present significantly higher SNR efficiency (171.3) than SPGR1 (158.7, p = 0.013) and SPGR2 (95.5, p < 10(-8)). iDESS CNR efficiency (19.2) is also significantly greater than SPGR1 (6.9, p < 10(-6)) and SPGR2 (14.3, p = 0.0016). Compared with DESS, iDESS provides further advantage on enhanced phase information and hence improved contrast on SWI-processed images.nnnCONCLUSIONSniDESS efficiently depicts midbrain nuclei with improved CNR efficiency, increased SNR efficiency, and reduced scan time and is less prone to susceptibility signal loss from air-tissue interfaces.