Clinical evaluation of 3D high-resolution isotropic knee MRI using Multi-Interleaved X-prepared TSE with inTUitive RElaxometry (MIXTURE) for simultaneous morphology and T2 mapping.

PURPOSE: Quantitative MRI techniques such as T2 mapping are useful in comprehensive evaluation of various pathologies of the knee joint yet require separate scans to conventional morphological measurements and long acquisition times. The recently introduced 3D MIXTURE (Multi-Interleaved X-prepared Turbo-Spin Echo with Intuitive Relaxometry) technique can obtain simultaneous morphologic and quantitative information of the knee joint. To compare MIXTURE with conventional methods and to identify differences in morphological and quantitative information. METHODS: Phantom studies were conducted, and in vivo human scans were performed (20 patients) presented with knee arthralgia. MIXTURE is based on 3D TSE without and with T2 preparation modules in an interleaved manner for both morphology with PDW and fat suppressed T2W imaging as well as quantitative T2 mapping within one single scan. Image quality and lesion depiction were visually assessed and compared between MIXTURE and conventional 2D TSE by two experienced radiologists. Contrast-to-noise ratio was used to assess the adjacent tissue contrast in a quantitative way for both obtained PDW and fat suppressed T2W images. Quantitative T2 values were measured in phantom and from in vivo knee cartilage. RESULTS: The overall diagnostic confidence and contrast-to-noise ratio were deemed comparable between MIXTURE and 2D TSE. While the chosen T2 preparation modules for MIXTURE rendered consistent T2 values comparing to the current standard, measured cartilage T2 values ranged from 26.1 to 50.7 ms, with significant difference between the lesion and normal areas (p < 0.05). CONCLUSIONS: MIXTURE can help to provide high-resolution information for both anatomical and pathological assessment.

Relationship between assistant's lens exposure and dose information during computed tomography examinations.

According to International Commission of Radiological Protection, the equivalent dose limit for the eye lens for occupational exposure is recommended to be 20 mSv yr-1, averaged over 5 years, with no single year above 50 mSv. Some studies reported the measurement of assistant's lens exposure in diagnostic computed tomography (CT) examinations, but further investigation is still required in the association between the lens dose for assistants and various dose parameters. Therefore, we measured the assistant's lens exposure using small optically stimulated luminescence dosimeters. The type of occupation, type of assistance, total scan time, total mAs, total scan length, and dose-length product (DLP) were recorded and analyzed in association with air kerma at the lens position. The assistance was classified into four types: 'assisted ventilation,' 'head holding,' 'body holding,' and 'raising patient's arm.' The air kerma of lens position was not significantly different for each assistance type (p< 0.05, Kruskal-Wallis test). Further, the lens doses for assistants correlated with DLP, but with various strengths of correlation with the assistance type and were influenced by the distance from the CT gantry. In conclusion, lens dose during assistance and DLP demonstrated the strongest correlation. 'Raising patient's arm' and 'head holding' exhibited stronger correlations, which required less table movement during the CT scan than 'assisted ventilation' and 'body holding'.

[Imaging Parameter Optimization of 3D Radial Stack-of-stars MRA with FID Sampling after Treatment of Cerebral Aneurysms with Metallic Devices].

Magnetic resonance angiography (MRA) using ultra-short TE (uTE) is known to be used for the evaluation of cerebral aneurysm after treatment such as clipping and coiling. However, conventional uTE sequences are not appropriate as an additional imaging sequence for 3D time-of-flight (TOF)-MRA because it is not possible to shorten scan time and acquire selective-volume imaging. To solve the problem, we focused on the combination of uTE sampling and 3D radial scan sequences. In this study, we examined the optimal imaging parameters of the proposed uTE-MRA. A simulated blood flow phantom with stents (Enterprise) and titanium clips (YASARGIL) was used for optimizing the TR, flip angle (FA), and radial percentage. The signal intensity in the simulated vessel was measured in each imaging condition, and the ratio of the presence or absence of a stent was evaluated as a relative in-stent signal (RIS). In addition, the diameter of the signal loss of the simulated artery was measured for each imaging condition, and signal loss length (SLL) of a clip was calculated from the average value. The RIS improved with increasing the FA and shortening the TR, but it did not change by changing the radial percentage. The SLL became smaller at the coil as the FA increased, but there was no significant difference between the intersection and the blade. There was also no significant difference between TR and radial percentage. The effective imaging conditions for uTE-MRA to improve the vascular description of the evaluation after treatment of cerebral aneurysms with metallic devices were those with large FA and short TR.

Does the increased motion probing gradient directional diffusion tensor imaging of lumbar nerves using multi-band SENSE improve the visualization and accuracy of FA values?

PURPOSE: Diffusion tensor imaging (DTI) is useful to evaluate lumbar nerves visually and quantitatively. Multi-band sensitivity encoding (MB-SENSE) is a technique to reduce the scan time. This study aimed to investigate if super-multi-gradient DTI with multi-band sensitivity encoding (MB-SENSE) is better in evaluating lumbar nerves than the conventional method. METHODS: The participants were 12 healthy volunteers (mean age 33.6 years). In all subjects, DTI was performed using echo planar imaging with different motion probing gradient (MPG) directions (15 without MB, and 15, 32, 64, and 128 with MB) and the lumbar nerve roots were visualized with tractography. In the five groups, we evaluated the resultant DTI both visually and quantitatively. For visual measures, we counted the number of fluffs and disruptions of the nerve fibers. For quantitative measures, the fractional anisotropy (FA) and standard deviation of the fractional anisotropy (FA-SD) values at two regions (proximal and distal) of the lumbar nerve roots were quantified and compared. RESULTS: Among the five groups, the number of fluffs decreased as the number of MPG directions increased. However, the number of disruptions showed no significant differences. The FA-SD values decreased as the number of MPG directions increased, indicating that the signal variation was reduced with multi-gradient directional DTI. CONCLUSION: High-resolution multi-directional DTI with MB-SENSE may be useful to visualize nerve entrapments and may allow for more accurate DTI parameter quantification with opportunities for clinical diagnostic applications.