Software for automated MRI-based quantification of abdominal fat and preliminary evaluation in morbidly obese patients.

To present software for supervised automatic quantification of visceral and subcutaneous adipose tissue (VAT, SAT) and evaluates its performance in terms of reliability, interobserver variation, and processing time, since fully automatic segmentation of fat-fraction magnetic resonance imaging (MRI) is fast but susceptible to anatomical variations and artifacts, particularly for advanced stages of obesity.Twenty morbidly obese patients (average BMI 44 kg/m(2) ) underwent 1.5-T MRI using a double-echo gradient-echo sequence. Fully automatic analysis (FAA) required no user interaction, while supervised automatic analysis (SAA) involved review and manual correction of the FAA results by two observers. Standard of reference was provided by manual segmentation analysis (MSA).Average processing times per patient were 6, 6+4, and 21 minutes for FAA, SAA, and MSA (P< 0.001), respectively. For VAT/SAT assessment, Pearson correlation coefficients, mean (bias), and standard deviations of the differences were R = 0.950, +0.003, and 0.043 between FAA and MSA and R = 0.981, +0.009, and 0.027 between SAA and MSA. Interobserver variation and intraclass correlation were 3.1% and 0.996 for SAA, and 6.6% and 0.986 for MSA, respectively.The presented supervised automatic approach provides a reliable option for MRI-based fat quantification in morbidly obese patients and was much faster than manual analysis. J. Magn. Reson. Imaging 2013;37:1144-1150. © 2012 Wiley Periodicals, Inc

In vivo MRI analysis of depth-dependent ultrastructure in human knee cartilage at 7 T

Signal intensities of T2-weighted magnetic resonance images depend on the local fiber arrangement in hyaline cartilage. The aims of this study were to determine whether angle-sensitive MRI at 7 T can be used to quantify the cartilage ultrastructure of the knee in vivo and to assess potential differences with age. Ten younger (21–30 ) and ten older (55–76 years old) healthy volunteers were imaged with a T2-weighted spin-echo sequence in a 7 T whole-body MRI. A “fascicle” model was assumed to describe the depth-dependent fiber arrangement of cartilage. The R/T boundary positions between radial and transitional zones were assessed from intensity profiles in small regions of interest in the femur and tibia, and normalized to cartilage thickness using logistic curve fits. The quality of our highly resolved (0.3 × 0.3 × 1.0 mm3) MR cartilage images were high enough for quantitative analysis (goodness of fit R2 = 0.91 ± 0.09). Between younger and older subjects, normalized positions of the R/T boundary, with value 0 at the bone–cartilage interface and 1 at the cartilage surface, were significantly (p < 0.05) different in femoral (0.51 ± 0.12 versus 0.41 ± 0.10), but not in tibial cartilage (0.65 ± 0.11 versus 0.57 ± 0.09, p = 0.119). Within both age groups, differences between femoral and tibial R/T boundaries were significant. Using a fascicle model and angle-sensitive MRI, the depth-dependent anisotropic fiber arrangement of knee cartilage could be assessed in vivo from a single 7 T MR image. The derived quantitative parameter, thickness of the radial zone, may serve as an indicator of the structural integrity of cartilage. This method may potentially be suitable to detect and monitor early osteoarthritis because the progressive disintegration of the anisotropic network is also indicative of arthritic changes in cartilage

Suitability of miniature inductively coupled RF coils as MR-visible markers for clinical purposes

Purpose: MR-visible markers have already been used for various purposes such as image registration, motion detection, and device tracking. Inductively coupled RF (ICRF) coils, in particular, provide a high contrast and do not require connecting wires to the scanner, which makes their application highly flexible and safe. This work aims to thoroughly characterize the MR signals of such ICRF markers under various conditions with a special emphasis on fully automatic detection. Methods: The small markers consisted of a solenoid coil that was wound around a glass tube containing the MR signal source and tuned to the resonance frequency of a 1.5 T MRI. Marker imaging was performed with a spoiled gradient echo sequence (FLASH) and a balanced steady-state free precession (SSFP) sequence (TrueFISP) in three standard projections. The signal intensities of the markers were recorded for both pulse sequences, three source materials (tap water, distilled water, and contrast agent solution), different flip angles and coil alignments with respect to theB 0 direction as well as for different marker positions in the entire imaging volume (field of view, FOV). Heating of the ICRF coils was measured during 10-min RF expositions to three conventional pulse sequences. Clinical utility of the markers was assessed from their performance in computer-aided detection and in defining double oblique scan planes. Results: For almost the entire FOV (±215 mm) and an estimated 82% of all possible RF coil alignments with respect toB 0, the ICRF markers generated clearly visible MR signals and could be reliably localized over a large range of flip angles, in particular with the TrueFISP sequence (0.3°–4.0°). Generally, TrueFISP provided a higher marker contrast than FLASH. RF exposition caused a moderate heating (≤5 °C) of the ICRF coils only. Conclusions : Small ICRF coils,imaged at low flip angles with a balanced SSFP sequence showed an excellent performance under a variety of experimental conditions and therefore make for a reliable, compact, flexible, and relatively safe marker for clinical use