Elisabeth Weiland

Optimal timing for in vivo 1H-MR spectroscopic imaging of the human prostate at 3T.

Proton MR spectroscopic imaging (1H‐MRSI) of the human prostate, which has an interesting clinical potential, may be improved by increasing the magnetic field strength from 1.5T to 3T. Both theoretical and practical considerations are necessary to optimize the pulse timing for spectroscopic imaging of the human prostate at 3T. For in vivo detection of the strongly coupled spin system of citrate, not only should the spectral shape of the signal be easy to identify, but the timing used should produce MR signals at reasonably short echo times (TEs). In this study the spectral shape of the methylene protons of citrate was simulated with density matrix calculations and checked with phantom measurements. Different calculated optimal spectral shapes were measured in patients with prostate cancer with a 2D spectroscopic imaging sequence. T1 and T2 relaxation times were calculated for citrate and choline, the two major metabolites of interest in the prostate. We conclude that the optimum timing for in vivo point‐resolved spectroscopy (PRESS) imaging at 3T is an interpulse timing sequence of 90° ‐ 25 ms ‐ 180° ‐ 37.5 ms ‐ 180° ‐ 12.5 ms ‐ echo. A short repetition time (TR) of 750 ms partially saturates choline signals, but increases the SNR per unit time for citrate, and accommodates a maximum number of weighted averages of an elliptically sampled k‐space for accurate localization and minimal contamination of the individual spectra. This is illustrated by means of a 3D spectroscopic imaging experiment in a complete prostate in vivo. Magn Reson Med 53:1268–1274, 2005.

Discriminating cancer from noncancer tissue in the prostate by 3-dimensional proton magnetic resonance spectroscopic imaging: a prospective multicenter validation study.

Objectives:A prospective multicenter validation of the ability of 1H magnetic resonance spectroscopic imaging (MRSI) to distinguish cancer from noncancer tissues throughout the prostate with histopathology of the resected organ as the standard of reference. Materials and Methods:Institutional review board approval was obtained for all centers and all participating patients and volunteers provided written informed consent. Ninety-nine patients and 10 age-matched volunteers from 8 participating centers underwent magnetic resonance imaging and 3-dimensional MRSI with an endorectal coil at 1.5 T. Selected MRSI voxels were assigned to the peripheral zone (PZ), the central gland (CG), the periurethral area, and cancer tissue. Signal ratios of choline + creatine to citrate (CC/C) in spectra of these voxels were automatically calculated. Receiver operating characteristic curves were constructed to assess the accuracy by which this ratio can discriminate cancer from noncancer tissue. Results:A total of 70% of voxels in noncancer tissue and 90% of voxels in cancer tissue passed the quality check of the automatically fitted spectra. The median CC/C was significantly different between any noncancer and cancer tissue (P < 0.0001), but not between the different contributing centers. CC/C increased with cancer focus size (P = 0.0008) and certainty of voxel mapping to histopathologic cancer site (P < 0.0001). The area under the receiver operating characteristic curve for discriminating voxels of cancer tissue from noncancer tissue was 0.88 (confidence interval: 0.84–0.92) in the PZ and 0.76 (confidence interval: 0.71–0.81) in the CG. Conclusions:In patients with prostate cancer, recruited from different institutions, 3-dimensional MRSI is demonstrated to be a robust and quantitative technique, producing significantly different CC/C values for cancer compared with noncancer tissue for both the CG and the PZ.

Metabolite ratios in 1H MR spectroscopic imaging of the prostate

In 1H MR spectroscopic imaging (1H‐MRSI) of the prostate the spatial distribution of the signal levels of the metabolites choline, creatine, polyamines, and citrate are assessed. The ratio of choline (plus spermine as the main polyamine) plus creatine over citrate [(Cho+(Spm+)Cr)/Cit] is derived from these metabolites and is used as a marker for the presence of prostate cancer. In this review, the factors that are of importance for the metabolite ratio are discussed. This is relevant, because the appearance of the metabolites in the spectrum depends not only on the underlying anatomy, metabolism, and physiology of the tissue, but also on acquisition parameters. These parameters influence especially the spectral shapes of citrate and spermine resonances, and consequently, the (Cho+(Spm+)Cr)/Cit ratio. Both qualitative and quantitative approaches can be used for the evaluation of 1H‐MRSI spectra of the prostate. For the quantitative approach, the (Cho+(Spm+)Cr)/Cit ratio can be determined by integration or by a fit based on model signals. Using the latter, the influence of the acquisition parameters on citrate can be taken into account. The strong overlap between the choline, creatine, and spermine resonances complicates fitting of the individual metabolites. This overlap and (unknown, possibly tissue‐related) variations in T1, T2, and J‐modulation hamper the application of corrections needed for a “normalized” (Cho+(Spm+)Cr)/Cit ratio that would enable comparison of spectra measured with different prostate MR spectroscopy protocols. Quantitative (Cho+(Spm+)Cr)/Cit thresholds for the evaluation of prostate cancer are therefore commonly established per institution or per protocol. However, if the same acquisition and postprocessing protocol were used, the ratio and the thresholds would be institution‐independent, promoting the clinical usability of prostate 1H‐MRSI. Magn Reson Med 73:1–12, 2015.

(31) P MR spectroscopic imaging of the human prostate at 7 T: T1 relaxation times, Nuclear Overhauser Effect, and spectral characterization

Optimization of phosphorus (31P) MR spectroscopic imaging (MRSI) of the human prostate at 7 T by the evaluation of T1 relaxation times and the Nuclear Overhauser Effect (NOE) of phosphorus‐containing metabolites.

Simultaneous multi-slice readout-segmented echo planar imaging for accelerated diffusion-weighted imaging of the breast.

OBJECTIVES Readout-segmented echo planar imaging (rs-EPI) significantly reduces susceptibility artifacts in diffusion-weighted imaging (DWI) of the breast compared to single-shot EPI but is limited by longer scan times. To compensate for this, we tested a new simultaneous multi-slice (SMS) acquisition for accelerated rs-EPI. MATERIALS AND METHODS After approval by the local ethics committee, eight healthy female volunteers (age, 38.9 ± 13.1 years) underwent breast MRI at 3T. Conventional as well as two-fold (2× SMS) and three-fold (3× SMS) slice-accelerated rs-EPI sequences were acquired at b-values of 50 and 800 s/mm(2). Two independent readers analyzed the apparent diffusion coefficient (ADC) in fibroglandular breast parenchyma. The signal-to-noise ratio (SNR) was estimated based on the subtraction method. ADC and SNR were compared between sequences by using the Friedman test. RESULTS The acquisition time was 4:21 min for conventional rs-EPI, 2:35 min for 2× SMS rs-EPI and 1:44 min for 3× SMS rs-EPI. ADC values were similar in all sequences (mean values 1.62 × 10(-3)mm(2)/s, p=0.99). Mean SNR was 27.7-29.6, and no significant differences were found among the sequences (p=0.83). CONCLUSION SMS rs-EPI yields similar ADC values and SNR compared to conventional rs-EPI at markedly reduced scan time. Thus, SMS excitation increases the clinical applicability of rs-EPI for DWI of the breast.

Reproducibility of 3D 1H MR spectroscopic imaging of the prostate at 1.5T

To determine the reproducibility of 3D proton magnetic resonance spectroscopic imaging (1H‐MRSI) of the human prostate in a multicenter setting at 1.5T.

Influence of brain tumors on the MR spectra of healthy brain tissue

The neurochemical environment of nontumorous white matter tissue was investigated in 135 single voxel spectra of “healthy” white matter regions of 43 tumor patients and 129 spectra of 52 healthy subjects. Spectra were acquired with short TE and TR values. With the data of tumor patients, it was examined whether differences were caused by the tumor itself or aggressive tumor therapies as confounding factors. Comparing the spectra of both classes, an excellent differentiation was possible based on the metabolite peak of N‐acetylaspartate (P ≈ 0) and myoinositol (P < 0.03). The area under curve of the receiver operating characteristic was calculated as 0.86 and 0.62, respectively. With linear discriminant analysis using combinations of integrals, a prediction was possible, whether a spectrum belonged to the patient or the healthy subject class with an overall accuracy above 80%. The confounding factors could be ruled out as source of the differences. The results show strong evidence for an influence of malignant growth on the biochemical environment of nontumorous white matter tissue. Because of the T1 weighting, the measured differences between both classes were most likely concentration changes interfered by T1 effects. The underlying processes will be subject of future studies. Magn Reson Med, 2010.

Improved volume selective (1) H MR spectroscopic imaging of the prostate with gradient offset independent adiabaticity pulses at 3 tesla

Volume selection in 1H MR spectroscopic imaging (MRSI) of the prostate is commonly performed with low‐bandwidth refocusing pulses. However, their large chemical shift displacement error (CSDE) causes lipid signal contamination in the spectral range of interest. Application of high‐bandwidth adiabatic pulses is limited by radiofrequency (RF) power deposition. In this study, we aimed to provide an MRSI sequence that overcomes these limitations.

Clinical Feasibility of 3-Dimensional Magnetic Resonance Cholangiopancreatography Using Compressed Sensing: Comparison of Image Quality and Diagnostic Performance

Objective The aim of this study was to evaluate the clinical feasibility of fast 3-dimensional (3D) magnetic resonance cholangiopancreatography (MRCP) using compressed sensing (CS) in comparison with conventional navigator-triggered 3D-MRCP. Materials and Methods This retrospective study was approved by our institutional review board, and the requirement of informed consent was waived. A total of 84 patients (male-to-female ratio, 41:43; mean age, 47.3 ± 18.8 years) who underwent conventional 3D navigator-triggered T2-weighted MRCP using sampling perfection with application optimized contrasts (SPACE) and fast 3D MRCP using SPACE with high undersampling combined with CS reconstruction (CS SPACE; CS-MRCP) on a 3 T scanner were included. Among them, 28 patients additionally underwent 3D breath-hold CS-MRCP (BH-CS-MRCP) with 5.7% k-space sampling. Three board-certified radiologists then independently reviewed the examinations for bile duct and pancreatic duct visualization and overall image quality on a 5-point scale, and image sharpness and background suppression on a 4-point scale, with the higher score indicating better image quality. In addition, diagnostic performance for the detection of anatomic variation and diseases of the bile duct, and pancreatic disease were assessed on a per-patient basis in the subgroup of 28 patients who underwent conventional MRCP, CS-MRCP, and BH-CS-MRCP in the same manner. Results Mean acquisition times of conventional MRCP, CS-MRCP, and BH-CS-MRCP were 7 minutes (419.7 seconds), 3 minutes 47 seconds (227.0 seconds), and 16 seconds, respectively (P < 0.0001, in all comparisons). In all patients, CS-MRCP showed better image sharpness (3.54 ± 0.60 vs 3.37 ± 0.75, P = 0.04) and visualization of the common bile duct (4.55 ± 0.60 vs 4.39 ± 0.78, P = 0.034) and pancreatic duct (3.47 ± 1.22 vs 3.26 ± 1.32, P = 0.025), but lower background suppression (3.00 ± 0.54 vs 3.37 ± 0.58, P < 0.001) than conventional MRCP. Overall image quality was not significantly different between the 2 examinations (3.51 ± 0.95 vs 3.47 ± 1.09, P = 0.75). The number of indeterminate MRCP examinations for the anatomic variation and disease of the bile duct significantly decreased on CS-MRCP, from 16.7%–22.6% to 9.5%–11.9% and 8.4%–15.6% to 3.6%–8.4% in all readers (P = 0.003–0.03). In the 28 patients who underwent BH-CS-MRCP, better image quality was demonstrated than with conventional MRCP and CS-MRCP (4.10 ± 0.84 vs 3.44 ± 1.21 vs 3.50 ± 1.11, respectively, P = 0.002, 0.001). Sensitivities for detecting bile duct disease was 88.9% to 100% on both BH-CS-MRCP and conventional MRCP (P > 0.05), and for detecting pancreatic disease was 66.7% to 83.3% on BH-CS-MRCP and 50.0% to 72.2% on conventional MRCP (P = 0.002 in reader 1, 0.06–0.47 in readers 2–3). Conclusions Compressed sensing MRCP using incoherent undersampling combined with CS reconstruction provided comparable image quality to conventional MRCP while reducing the acquisition time to within a single breath-hold (16 seconds).

Time to enhancement derived from ultrafast breast MRI as a novel parameter to discriminate benign from malignant breast lesions

OBJECTIVES To investigate time to enhancement (TTE) as novel dynamic parameter for lesion classification in breast magnetic resonance imaging (MRI). METHODS In this retrospective study, 157 women with 195 enhancing abnormalities (99 malignant and 96 benign) were included. All patients underwent a bi-temporal MRI protocol that included ultrafast time-resolved angiography with stochastic trajectory (TWIST) acquisitions (1.0×0.9×2.5mm, temporal resolution 4.32s), during the inflow of contrast agent. TTE derived from TWIST series and relative enhancement versus time curve type derived from volumetric interpolated breath-hold examination (VIBE) series were assessed and combined with basic morphological information to differentiate benign from malignant lesions. Receiver operating characteristic analysis and kappa statistics were applied. RESULTS TTE had a significantly better discriminative ability than curve type (p<0.001 and p=0.026 for reader 1 and 2, respectively). Including morphology, sensitivity of TWIST and VIBE assessment was equivalent (p=0.549 and p=0.344, respectively). Specificity and diagnostic accuracy were significantly higher for TWIST than for VIBE assessment (p<0.001). Inter-reader agreement in differentiating malignant from benign lesions was almost perfect for TWIST evaluation (κ=0.86) and substantial for conventional assessment (κ=0.75). CONCLUSIONS TTE derived from ultrafast TWIST acquisitions is a valuable parameter that allows robust differentiation between malignant and benign breast lesions with high accuracy.