Wilhelm Horger

Magnetic resonance imaging of the body trunk using a single-slab, 3-dimensional, T2-weighted turbo-spin-echo sequence with high sampling efficiency (SPACE) for high spatial resolution imaging: Initial clinical experiences

Purpose:The authors conducted a clinical evaluation of single-slab, 3-dimensional, T2-weighted turbo-spin-echo (TSE) with high sampling efficiency (SPACE) for high isotropic body imaging with large field-of-view (FoV). Materials and Methods:Fifty patients were examined in clinical routine with SPACE (regions of interest: pelvis n = 30, lower spine n = 12, upper spine n = 6, extremities n = 4) at 1.5 T. For achieving a high sampling efficiency, parallel imaging, high turbofactor, and magnetization restore pulses were used. In contrast to a conventional TSE imaging technique with constant flip angle refocusing, the refocusing pulse train of the SPACE sequence consists of variable flip angle radiofrequency pulses along the echo train. Results:Signal-to-noise ratio and contrast-to-noise ratio of SPACE images were of sufficient diagnostic value. The possibility of image reconstruction in multiple planes was of clinical relevance in all cases and simplified data analysis. Conclusion:The achievement of 3-dimensional, T2-weighted TSE magnetic resonance imaging with isotropic and high spatial resolution and interactive 3-dimensional visualization essentially improve the diagnostic potential of magnetic resonance imaging.

Quantitative T2 mapping of matrix-associated autologous chondrocyte transplantation at 3 Tesla: an in vivo cross-sectional study.

Objectives:To evaluate magnetic resonance (MR) T2 mapping for characterization of cartilage repair tissue following matrix-associated autologous cartilage transplantation (MACT). Materials and Methods:Fifteen patients were evaluated following MACT using a 3T MR scanner. Patients were categorized into 2 postoperative intervals: I: 3–13 months, II: 19–42 months. Mean T2 relaxation times calculated from multiple spin-echo sequence were determined in regions of interest (MACT and normal hyaline cartilage) and T2 line profiles through the repair tissue and control sites were acquired. Results:Mean global T2 values of repair tissue in group I were significantly higher than at control sites (P < 0.05). Repair tissue in group II showed no significant difference to control sites. Repair tissue T2 line profiles normalized over time toward the control sites. Conclusions:T2 mapping allows visualization of cartilage repair tissue maturation. Global T2 repair tissue values approach that of control sites after more than 1.5 years, similar behavior is seen in the zonal organization.

Black-Blood Diffusion-Weighted EPI Acquisition of the Liver with Parallel Imaging : Comparison with a Standard T2-Weighted Sequence for Detection of Focal Liver Lesions

Objectives:To evaluate the performance of black-blood diffusion-weighted (DW)-EPI sequences with parallel imaging for the detection of focal liver lesions in comparison with a standard T2-weighted (T2-w) sequence. Materials and Methods:Twenty patients with known or suspected focal liver lesions underwent liver MRI using a DW-EPI sequence with a b-value of 50 S/mm2 (TR/TE 2200/50 ms) and a standard fat-saturated T2-w sequence (TR/TE 2800/107 ms) with 6-mm slice thickness on a 1.5-T MRI system. Both sequences used parallel imaging with an acceleration factor of 2. Overall image quality and degree of artifacts were compared on a 5-point scale with 5 being the most desirable score. The detection rate and the level of confidence with regard to lesion detection were evaluated for both sequences in comparison to a contrast-enhanced (Gadolinium and SPIO) MR examination, which was used as the standard of reference. Results:The DW-EPI sequence showed significantly (P < 0.05) improved overall image quality (average score 4.15 vs. 3.63) and fewer artifacts (average score 4.2 vs. 3.5) in comparison with the T2-w sequence. The sensitivity for lesion detection was superior in the DW-EPI sequence (83% vs. 61%). The level of confidence in the detection of focal liver lesions was also superior for the DW-EPI sequence in comparison with the T2-w sequence (average score 3.9 vs. 3.2). Conclusions:DW-EPI sequences for liver-imaging are feasible with parallel imaging and show excellent image quality. They may contribute to more easy and confident lesion detection in comparison with T2-w sequences.

Tumor detection by Diffusion Weighted MRI and ADC-Mapping - Initial Clinical Experiences in Comparison to PET-CT

Objective:To evaluate the clinical potential of diffusion-weighted-imaging (DWI) with apparent diffusion coefficient (ADC)-mapping for tumor detection. Materials and Methods:A single-shot echo-planar-imaging DWI sequence with fat suppression and ability for navigator-based respiratory triggering was implemented. Nineteen patients (11 melanoma, 4 prostate cancer, 1 non-Hodgkin lymphoma, and 3 lung cancer) were examined by positron emission tomography (PET) with an integrated computed tomography scanner (PET-CT) and DWI. Images at b = 0, 400, and 1000 s/mm2 were acquired and ADC maps were generated. PET examinations were used as a reference for tumor detection. Four hundred twenty-four regions of interest were used for DWI and 73 for PET data evaluation. Results:DWI and ADC maps were of diagnostic quality. Metastases with increased tracer uptake were clearly visualized at b = 1000 s/mm2 with the exception of mediastinal lymph node metastases in cases of lung cancer. ADC mapping did not improve detection rates. Conclusions:DWI is a feasible clinical technique, improving the assessment of metastatic spread in routine magnetic resonance imaging examinations.

MRI of the Knee at 3T: First Clinical Results With an Isotropic PDfs-Weighted 3D-TSE-Sequence

Purpose:To clinically evaluate MRI of the knee using a highly resolved isotropic fat-saturated (fs) proton-density weighted 3D-TSE-sequence (SPACE) at 3T. Materials and Methods:Imaging was performed on a 3T-scanner (Magnetom TRIO). For technical evaluation, sagittally orientated SPACE-datasets (repetition-time [TR], 1200 milliseconds/[TE], 30 milliseconds/voxel-size, 0.5 mm3/acquisition time, 10:35 minutes) were acquired from the dominant knee of 10 healthy volunteers. In the 3 major anatomic planes, 0.5, 1, and 2 mm thick reconstructions were performed. Signal-to-noise (SNR), SNR-efficiency, contrast-to-noise (CNR) ratios, and anatomic detail visualization were compared with a state-of-the-art 2D-TSE-sequence in 3 imaging planes (TR, 3200 milliseconds/TE, 30 milliseconds/acquisition time, 12:34 minutes). Sixty patients with cartilage and meniscus pathologies were examined with these techniques. Patient SPACE-datasets were assessed in 1-mm thick reconstructions. Arthroscopical correlation was available for 18 patients. Lesion detection and diagnostic confidence were assessed by 2 radiologists independently. Statistical analysis was performed using 95% confidence intervals, Wilcoxon signed rank tests, and Weighted-&kgr;. Results:SNR-efficiency of SPACE was 4 to 5 times higher than for 2D-TSE-sequences. SNR and CNR of 1-mm thick SPACE-reconstructions were comparable to 2D-TSE-sequences and provided superior visualization of small structures such as meniscal roots.Correlation with arthroscopy did not show significant differences between 2D- and 3D-sequences. One reader detected significantly more cartilage abnormalities with the 2D-TSE-sequence (131 vs. 151, P = 0.04), probably because of an unfamiliar fluid/cartilage contrast. Diagnostic confidence was significantly higher for meniscus abnormalities for SPACE for 1 reader. Intersequence-correlation was excellent (&kgr; = 0.82–0.92). Interreader-correlation was good to excellent (&kgr; = 0.71–0.80), intrareader-correlation was excellent (&kgr; = 0.90–0.92) for both sequences. Conclusions:Time-efficient 3D-TSE-imaging of the knee at 3T is feasible with adequate SNR and CNR and excellent anatomic detail visualization. Detection and visualization of meniscus and cartilage pathologies is comparable to standard 2D-TSE-sequences. 3D-TSE-sequences with consecutive multiplanar reconstruction may become a valuable component of future knee-MRI protocols.

Whole-body diffusion-weighted MRI with apparent diffusion coefficient mapping for early response monitoring in multiple myeloma: preliminary results.

OBJECTIVE The purpose of our study was to prospectively assess the feasibility of whole-body diffusion-weighted imaging (DWI) for short-term evaluation of response to treatment in multiple myeloma patients using a single-shot echo-planar imaging DWI sequence with a Stejskal-Tanner diffusion encoding scheme and spectral fat suppression. SUBJECTS AND METHODS Twelve consecutive patients (nine men and three women; mean age, 61.4 years; age range, 54-79 years) underwent whole-body DWI (b = 50, 400, and 800 s/mm(2)) both at baseline and 3 weeks (mean, 23 days) after onset of therapy. Bone marrow and extramedullary manifestations were evaluated by quantitative image analysis using measurements of the mean apparent diffusion coefficient (ADC). These parameters were correlated with myeloma response according to standard criteria and were evaluated parallel to MRI and continuously for more than 6 months afterward. RESULTS Fifty-three myeloma lesions, 50 medullary (28 axial and 22 appendicular skeleton) and three extramedullary, were analyzed. Eleven patients were classified as responders and one as a nonresponder. DWI results accurately (100%) correlated with disease course according to standard clinical and laboratory criteria. All involved lesions showed restricted diffusion at baseline. ADC quantification yielded an increase of 63.9% (range, 8.7-211.3%) in responders and a decrease of 7.8% in the sole nonresponding patient during therapy. In parallel, M-gradient measurement showed a mean decrease of 45.1% (range, 19.6-88.8%) in responders and an increase of 21.8% in the nonresponder. Amplitude of response measured by the course of ADC values proved higher in the appendicular skeleton (99.8%) compared with the axial skeleton (54.3%) (p = 0.037). CONCLUSION Whole-body DWI with ADC analysis represents a feasible diagnostic tool for assessment of short-term treatment response in myeloma patients.

Optimized T1-weighted contrast for single-slab 3D turbo spin-echo imaging with long echo trains: Application to whole-brain imaging

T1‐weighted contrast is conventionally obtained using multislice two‐dimensional (2D) spin‐echo (SE) imaging. Achieving isotropic, high spatial resolution is problematic with conventional methods due to a long acquisition time, imperfect slice profiles, or high‐energy deposition. Single‐slab 3D SE imaging was recently developed employing long echo trains with variable low flip angles to address these problems. However, long echo trains may yield suboptimal T1‐weighted contrast, since T2 weighting of the signals tends to develop along the echo train. Image blurring may also occur if high spatial frequency signals are acquired with low signal intensity. The purpose of this work was to develop an optimized T1‐weighted version of single‐slab 3D SE imaging with long echo trains. Refocusing flip angles were calculated based on a tissue‐specific prescribed signal evolution. Spatially nonselective excitation was used, followed by half‐Fourier acquisition in the in‐plane phase encoding (PE) direction. Restore radio frequency (RF) pulses were applied at the end of the echo train to optimize T1‐weighted contrast. Imaging parameters were optimized by using Bloch equation simulation, and imaging studies of healthy subjects were performed to investigate the feasibility of whole‐brain imaging with isotropic, high spatial resolution. The proposed technique permitted highly‐efficient T1‐weighted 3D SE imaging of the brain. Magn Reson Med 58:982–992, 2007.

High-resolution cartilage imaging of the knee at 3 T: Basic evaluation of modern isotropic 3D MR-sequences

PURPOSE To evaluate qualitative and quantitative image quality parameters of isotropic three-dimensional (3D) cartilage-imaging magnetic resonance (MR)-sequences at 3T. MATERIALS AND METHODS The knees of 10 healthy volunteers (mean age, 24.4±5.6 years) were scanned at a 3T MR scanner with water-excited 3D Fast-Low Angle Shot (FLASH), True Fast Imaging with Steady-state Precession (TrueFISP), Sampling Perfection with Application-optimized Contrast using different flip-angle Evolutions (SPACE) as well as conventional and two individually weighted Double-Echo Steady-State (DESS) sequences. The MR images were evaluated qualitatively and quantitatively (signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), SNR efficiency, CNR efficiency). Quantitative parameters were compared by means of a Tukey-test and sequences were ranked according to SNR/CNR, SNR/CNR efficiency and qualitative image grading. RESULTS The highest SNR was measured for SPACE (34.0±5.6), the highest CNR/CNR efficiency (cartilage/fluid) for the individually weighted DESS (46.9±18.0/2.18±0.84). SPACE, individually weighted and conventional DESS were ranked best with respect to SNR/CNR and SNR/CNR efficiency. The DESS sequences also performed best in the qualitative evaluation. TrueFISP performed worse, FLASH worst. The individually weighted DESS sequences were generally better than the conventional DESS with the significant increase of cartilage-fluid contrast (46.9±18.0/31.9±11.4 versus 22.0±7.3) as main advantage. CONCLUSION Individually weighted DESS is the most promising candidate; all tested sequences performed better than FLASH.

Quantitative assessment of patellar cartilage volume and thickness at 3.0 tesla comparing a 3d-fast low angle shot versus a 3d-true fast imaging with steady-state precession sequence for reproducibility

Objectives:We sought to compare patellar cartilage volume and thickness measurement between 3D-FLASH and 3D-True fast imaging with steady-state precession (FISP) image data at 3.0 T. Materials and Methods:One knee each of 6 healthy adults was examined by axial magnetic resonance imaging (MRI) performed with a 3D-fast flow angle shot (FLASH) water-excitation sequence and a 3D-TrueFISP water-excitation sequence (spatial resolution 0.31 × 0.31 × 1.5 mm3). Patellar cartilage volume and mean/maximum thickness were calculated. Intraindividual/average reproducibility and interindividual variability were determined from 3 consecutive data sets acquired for each volunteer and sequence. Results:Patellar cartilage volume and thickness as well as reproducibility was slightly but not significantly lower for the 3D-TrueFISP data than for the 3D-FLASH data (volume: 3.4–6.3 mL (3D-FLASH)/3.1–6.0 mL (3D-TrueFISP), average reproducibility 1.8% (3D-FLASH)/4.4% (3D-TrueFISP); mean thickness: 2.1–2.8 mm (3D-FLASH)/1.9–2.6 mm (3D-TrueFISP), average reproducibility 2.8% (3D-FLASH)/3.8% (3D-TrueFISP); maximum thickness: 4.7–6.6 mm (3D-FLASH)/4.5–6.2 mm (3D-TrueFISP), average reproducibility 2.6% (3D-FLASH)/4.1% (3D-TrueFISP)). Interindividual variability was comparable for both sequence techniques. Conclusion:At 3.0 T, the 3D-FLASH sequence showed tendency to be slightly superior to the 3D-TrueFISP sequence considering robust and valid assessment of quantitative cartilage parameters in young healthy adults, although there was found no significant statistical difference between both imaging techniques. However, in patients suffering from osteoarthritis (OA), the 3D-TrueFISP sequence might prove advantageous for monitoring of disease progression and evaluation of therapy success, particularly because the substantially higher signal to noise ratio/contrast to noise ratio values might allow for higher spatial resolution and hence for improvement of the accuracy of segmentation process especially at the articular surface.

Understanding 3D TSE Sequences: Advantages, Disadvantages, and Application in MSK Imaging.

Three-dimensional (3D) turbo-spin echo (TSE) sequences have outgrown the stage of mere sequence optimization and by now are clinically applicable. Image blurring and acquisition times have been reduced, and contrast for T1-, T2-, and moderately T2-weighted (or intermediate-weighted) fat-suppressed variants has been optimized. Data on sound-to-noise ratio efficiency and contrast are available for moderately T2-weighted fat-saturated sequence protocols. The 3-T MRI scanners help to better exploit isotropic spatial resolution and multiplanar reformatting. Imaging times range from 5 to 10 minutes, and they are shorter than the cumulative acquisition times of three separate orthogonal two-dimensional (2D) sequences. Recent suggestions go beyond secondary reformations by using online 3D rendering for image evaluation. Comparative clinical studies indicate that the diagnostic performance of 3D TSE for imaging of internal derangements of joints is at least comparable with conventional 2D TSE with potential advantages of 3D TSE for small highly curved structures. But such studies, especially those with direct arthroscopic correlation, are still sparse. Whether 3D TSE will succeed in entering clinical routine imaging on a broader scale will depend on further published clinical evidence, on further reduction of imaging time, and on improvement of its integration into daily practice.