Roman Guggenberger

Quantification of muscle fat in patients with low back pain: comparison of multi-echo MR imaging with single-voxel MR spectroscopy.

PURPOSE To compare lumbar muscle fat-signal fractions derived from three-dimensional dual gradient-echo magnetic resonance (MR) imaging and multiple gradient-echo MR imaging with fractions from single-voxel MR spectroscopy in patients with low back pain. MATERIALS AND METHODS This prospective study had institutional review board approval, and written informed consent was obtained from all study participants. Fifty-six patients (32 women; mean age, 52 years ± 15 [standard deviation]; age range, 20-79 years) with low back pain underwent standard 1.5-T MR imaging, which was supplemented by dual-echo MR imaging, multi-echo MR imaging, and MR spectroscopy to quantify fatty degeneration of bilateral lumbar multifidus muscles in a region of interest at the intervertebral level of L4 through L5. Fat-signal fractions were determined from signal intensities on fat- and water-only images from both imaging data sets (dual-echo and multi-echo fat-signal fractions without T2* correction) or directly obtained, with additional T2* correction, from multi-echo MR imaging. The results were compared with MR spectroscopic fractions. The Student t test and Bland-Altman plots were used to quantify agreement between fat-signal fractions derived from imaging and from spectroscopy. RESULTS In total, 102 spectroscopic measurements were obtained bilaterally (46 of 56) or unilaterally (10 of 56). Mean spectroscopic fat-signal fraction was 19.6 ± 11.4 (range, 5.4-63.5). Correlation between spectroscopic and all imaging-based fat-signal fractions was statistically significant (R(2) = 0.87-0.92; all P < .001). Mean dual-echo fat-signal fractions not corrected for T2* and multi-echo fat-signal fractions corrected for T2* significantly differed from spectroscopic fractions (both P < .01), but mean multi-echo fractions not corrected for T2* did not (P = .11). There was a small measurement bias of 0.5% (95% limits of agreement: -6.0%, 7.2%) compared with spectroscopic fractions. CONCLUSION Large-volume image-based (dual-echo and multi-echo MR imaging) and spectroscopic fat-signal fractions agree well, thus allowing fast and accurate quantification of muscle fat content in patients with low back pain.

Diagnostic Performance of Dual-Energy CT for the Detection of Traumatic Bone Marrow Lesions in the Ankle: Comparison with MR Imaging

PURPOSE To evaluate prospectively the performance of noncalcium images reconstructed from dual-energy (DE) computed tomography (CT) for the diagnosis of bone marrow lesions in patients with acute ankle joint trauma in comparison with magnetic resonance (MR) images. MATERIALS AND METHODS The study had local ethics board approval, and written informed consent was obtained. Thirty consecutive patients (15 women; mean age, 34 years±11.8 [standard deviation]) underwent dual-source DE CT (80 kVp and 140 kVp with tin filter) and MR imaging within 1 day following acute ankle trauma. DE CT data were postprocessed by using a three-material decomposition algorithm for generating noncalcium images. MR and noncalcium images were graded by two blinded, independent readers using a four-point system (1=distinct bone marrow lesion, 4=no lesion); CT numbers in noncalcium images were calculated by a third reader. MR imaging interpretations served as the reference standard. RESULTS Interreader agreement for qualitative grading of DE CT images was substantial (κ=0.66). The respective sensitivity, specificity, positive predictive value, and negative predictive value of DE CT for depicting distinct bone marrow lesions for both readers were 90.0% each, 80.5% and 81.6%, 25.4% and 26.5%, and 99.1% each. In regions without abnormality, CT numbers in noncalcium images gradually increased from proximal to distal location (P<.001). Significant differences in CT numbers were found in regions positive for bone marrow lesions compared with those that were negative (P<.001). CT numbers for the diagnosis of distinct bone marrow lesions according to MR imaging revealed areas under the receiver operating characteristic curve of 0.973, 0.813, and 0.758 for ankle mortise, talar dome, and talar body/head, respectively. CONCLUSION Compared with MR images, distinct traumatic bone marrow lesions of the ankle joint can be diagnosed on noncalcium images reconstructed from DE CT with high sensitivity and excellent negative predictive value, but with moderate specificity and low positive predictive value.

Femoral and Tibial Torsion Measurements With 3D Models Based on Low-Dose Biplanar Radiographs in Comparison With Standard CT Measurements

OBJECTIVE The purpose of this study was to evaluate the interchangeability of femoral and tibial torsion measurements obtained with 3D models based on low-dose biplanar radiographs and standard CT measurements by testing the following two hypotheses: that there is excellent agreement between the two methods and that there is excellent interreader agreement. MATERIALS AND METHODS Two independent readers used 3D models based on low-dose simultaneous biplanar radiographs and axial CT images to measure femoral and tibial torsion in 35 patients (mean age, 65 years; range, 46-89 years) with osteoarthritis of the knee who were to undergo prosthesis insertion. The two measurements were compared by means of Bland-Altman plots and descriptive statistics. Interreader agreement was quantified with intraclass correlation coefficients. RESULTS The average differences between readers on the CT measurements were 1.3° (range, 0°-11°) for the femur and 1.5° (range, 0°-12°) for the tibia. The average differences for the measurements obtained with the 3D model were 0.1° (range, 0°-9°) for the femur and 0.8° (range, 0°-10°) for the tibia. The average differences between the two methods were 0° (range, -5° to 7°) for the femoral measurements and 3° (range, -12° to 5°) for the tibial measurements. Bland-Altman plots showed no relevant differences between the results of the two measurement modalities. Except for one measurement of femoral torsion and one measurement of tibial torsion, all results based on the 3D models were within the 95% limit of agreement (mean ± 1.96 SD). Interreader agreement was statistically significant (p < 0.001) for all measurements with high intraclass correlation coefficients (> 0.9). CONCLUSION Femoral and tibial torsion measurements obtained with 3D models based on biplanar radiographs are interchangeable with standard CT measurements in patients with osteoarthritis of the knee.

Human hand radiography using X-ray differential phase contrast combined with dark-field imaging

Established X-ray-based imaging procedures such as conventional radiography and computed tomography (CT) rely on the interaction of photons when passing through tissue, including the Compton scattering and the photoelectric effect, which is influenced by the X-ray energy and the type of matter. The resulting mean attenuation of X-rays can be measured and depicted on images with different gray levels. X-ray phase contrast imaging (PCI) represents a relatively new imaging technique relying upon the refraction of Xrays. As such, PCI relies on a fundamentally different physical contrast mechanism compared with conventional, absorption-based X-ray imaging. In the energy range of diagnostic imaging (10–120 keV), refraction is the dominant effect over absorption, but more difficult to acquire. Previous studies have demonstrated that PCI can provide considerably higher contrast in soft tissue, giving rise to its application in fields where conventional radiography and CT are usually limited. Among a variety of techniques used to acquire phase contrast images, grating interferometry [1] has recently attracted great attention because of its compatibility with conventional X-ray tubes [2, 3], which is the key prerequisite for the clinical applicability. In addition, this technique provides a third contrast mode along with absorption and phase contrast, which is the dark-field contrast [4]. Similarly, dark-field imaging again exploits a physically different interaction mechanism and represents the intensity of the scattered X-rays within the area of a single detector pixel. Image pixels with high gray values indicate strong scattering. Recent studies have investigated the performance of phase contrast (PC) and dark-field contrast (DC) in the imaging of female breast tissue, indicating promising results for distinguishing microcalcifications and the malignant conversion or extension of the carcinoma into normal breast tissue [5, 6]. Yet, joint pathologies such as rheumatoid arthritis, crystal arthropathies, and connective tissue diseases (e.g., scleroderma), are also associated with soft tissue affection and occasional calcifications. Conventional radiography of the hand is a cornerstone imaging study for the detection and monitoring of joint diseases as subtle changes of joint space and bones (narrowing and erosions or osteophytes) and—if perceivable—of soft tissue (including calcifications and fibrosis) [7, 8], indicating disease activity and/or progress. While tissue evaluation with conventional radiography is based on morphological criteria Electronic supplementary material The online version of this article (doi:10.1007/s00256-013-1606-7) contains supplementary material, which is available to authorized users T. Thuring (*) : Z. Wang :C. David :M. Stampanoni Paul Scherrer Institut, WBBA/213, 5232, Villigen, Switzerland e-mail: thomas.thuering@psi.ch

MR neurography of the median nerve at 3.0 T: Optimization of diffusion tensor imaging and fiber tractography

OBJECTIVES The purpose of this study was to systematically assess the optimal b-value and reconstruction parameters for DTI and fiber tractography of the median nerve at 3.0T. METHODS Local ethical board approved study with 45 healthy volunteers (15 men, 30 women; mean age, 41 ± 3.4 years) who underwent DTI of the right wrist at 3.0T. A single-shot echo-planar-imaging sequence (TR/TE 10123/40 ms) was acquired at four different b-values (800, 1000, 1200, and 1400 s/mm(2)). Two independent readers performed post processing and fiber-tractography. Fractional anisotropy (FA) maps were calculated. Fiber tracts of the median nerve were generated using four different algorithms containing different FA thresholds and different angulation tolerances. Data were evaluated quantitatively and qualitatively. RESULTS Tracking algorithms using a minimum FA threshold of 0.2 and a maximum angulation of 10° were significantly better than other algorithms. Fiber tractography generated significantly longer fibers in DTI acquisitions with higher b-values (1200 and 1400 s/mm(2) versus 800 s/mm(2); p<0.001). The overall quality of fiber tractography was best at a b-value of 1200 s/mm(2) (p<0.001). CONCLUSIONS In conclusion, our results indicate use of b-values between 1000 and 1400 s/mm(2) for DTI of the median nerve at 3.0T. Optimal reconstruction parameters for fiber tractography should encompass a minimum FA threshold of 0.2 and a maximum angulation tolerance of 10.

Dynamic intravoxel incoherent motion imaging of skeletal muscle at rest and after exercise.

The purpose of this work was to demonstrate the feasibility of intravoxel incoherent motion imaging (IVIM) for non‐invasive quantification of perfusion and diffusion effects in skeletal muscle at rest and following exercise.

CT metal artefact reduction for internal fixation of the proximal humerus: Value of mono-energetic extrapolation from dual-energy and iterative reconstructions

AIM To assess the value of dual-energy computed tomography (DECT) and an iterative frequency split-normalized metal artefact reduction (IFS-MAR) algorithm compared to filtered back projections (FBP) from single-energy CT (SECT) for artefact reduction in internally fixated humeral fractures. MATERIALS AND METHODS Six internally fixated cadaveric humeri were examined using SECT and DECT. Data were reconstructed using FBP, IFS-MAR, and mono-energetic DECT extrapolations. Image analysis included radiodensity values and qualitative evaluation of artefacts, image quality, and level of confidence for localizing screw tips. RESULTS Radiodensity values of streak artefacts were significantly different (p < 0.05) between FBP (-104 ± 222) and IFS-MAR (73 ± 122), and between FBP and DECT (32 ± 151), without differences between IFS-MAR and DECT (p < 0.553). Compared to FBP, qualitative artefacts were significantly reduced using IFS-MAR (p < 0.001) and DECT (p < 0.05), without significant differences between IFS-MAR and DECT (p < 0.219). Image quality significantly (p = 0.016) improved for IFS-MAR and DECT compared to FBP, without significant differences between IFS-MAR and DECT (p < 0.553). The level of confidence for screw tip localization was assessed as best for DECT in all cases. CONCLUSION Both IFS-MAR in SECT and mono-energetic DECT produce improved image quality and a reduction of metal artefacts. Screw tip positions can be most confidently assessed using DECT.

Simultaneous Multislice Echo Planar Imaging With Blipped Controlled Aliasing in Parallel Imaging Results in Higher Acceleration A Promising Technique for Accelerated Diffusion Tensor Imaging of Skeletal Muscle

ObjectiveThe aim of this study was to investigate the feasibility of accelerated diffusion tensor imaging (DTI) of skeletal muscle using echo planar imaging (EPI) applying simultaneous multislice excitation with a blipped controlled aliasing in parallel imaging results in higher acceleration unaliasing technique. Materials and MethodsAfter federal ethics board approval, the lower leg muscles of 8 healthy volunteers (mean [SD] age, 29.4 [2.9] years) were examined in a clinical 3-T magnetic resonance scanner using a 15-channel knee coil. The EPI was performed at a b value of 500 s/mm2 without slice acceleration (conventional DTI) as well as with 2-fold and 3-fold acceleration. Fractional anisotropy (FA) and mean diffusivity (MD) were measured in all 3 acquisitions. Fiber tracking performance was compared between the acquisitions regarding the number of tracks, average track length, and anatomical precision using multivariate analysis of variance and Mann-Whitney U tests. ResultsAcquisition time was 7:24 minutes for conventional DTI, 3:53 minutes for 2-fold acceleration, and 2:38 minutes for 3-fold acceleration. Overall FA and MD values ranged from 0.220 to 0.378 and 1.595 to 1.829 mm2/s, respectively. Two-fold acceleration yielded similar FA and MD values (P ≥ 0.901) and similar fiber tracking performance compared with conventional DTI. Three-fold acceleration resulted in comparable MD (P = 0.199) but higher FA values (P = 0.006) and significantly impaired fiber tracking in the soleus and tibialis anterior muscles (number of tracks, P < 0.001; anatomical precision, P ⩽ 0.005). ConclusionsSimultaneous multislice EPI with blipped controlled aliasing in parallel imaging results in higher acceleration can remarkably reduce acquisition time in DTI of skeletal muscle with similar image quality and quantification accuracy of diffusion parameters. This may increase the clinical applicability of muscle anisotropy measurements.

Diffusion tensor imaging of the median nerve at 3.0 T using different MR scanners: agreement of FA and ADC measurements.

OBJECTIVE To assess the agreement of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of the median nerve on 3.0 T MR scanners from different vendors. MATERIALS AND METHODS IRB approved study including 16 healthy volunteers (9 women; mean age 30.6 ± 5.3 years). Diffusion tensor imaging (DTI) of the dominant wrist was performed on three 3.0 T MR scanners (GE, Siemens, Philips) using similar imaging protocols and vendor-proprietary hard- and software. Intra-, inter-reader and inter-vendor agreements were assessed. RESULTS ICCs for intra-/inter-reader agreements ranged from 0.843-0.970/0.846-0.956 for FA, and 0.840-0.940/0.726-0.929 for ADC, respectively. ANOVA analysis identified significant differences for FA/ADC measurements among vendors (p < 0.001/p < 0.01, respectively). Overall mean values for FA were 0.63 (SD ± 0.1) and 0.999 × 10(-3)mm(2)/s (SD ± 0.134 × 10(-3)) for ADC. A significant negative measurement bias was found for FA values from the GE scanner (-0.05 and -0.07) and for ADC values from the Siemens scanner (-0.053 and -0.063 × 10(-3)mm(2)/s) as compared to the remainder vendors CONCLUSION FA and ADC values of the median nerve obtained on different 3.0 T MR scanners differ significantly, but are in comparison to the standard deviation of absolute values small enough to not have an impact on larger group studies or when substantial diffusion changes can be expected. However, caution is warranted in an individual patient when interpreting diffusion values from different scanner acquisitions.

Flat-panel CT arthrography: feasibility study and comparison to multidetector CT arthrography.

Objectives:To show the feasibility of flat-panel computed tomography (FPCT) arthrography and quantitatively and qualitatively compare different FPCT protocols with standard multidetector computed tomography (MDCT). Materials and Methods:First, a phantom simulating joint space with increasing iodine concentrations was scanned using a standard MDCT and 3 different FPCT protocols. Quantitative analyses were performed by measuring CT numbers of iodine dilutions, radiation dose, and image noise as well as signal-to-noise ratio and contrast-to-noise ratio. Second, FPCT arthrographies of 4 animal joint specimens were performed and analyzed qualitatively by 2 independent readers who evaluated image artifacts, image noise, overall image quality and anatomic depiction of bone, cartilage, and soft tissue. Kappa values were calculated for inter-reader agreement. Pearsons correlation coefficient (r) and Wilcoxon signed-ranks test with Bonferroni corrections for multiple comparisons were used to compare MDCT and FPCT. Results:In phantoms, all CT scans showed a linear correlation between increasing iodine concentrations and mean HU values of contrast media and radiation dose, respectively (r = 0.98–0.99, P < 0.01). Dose-length product remained constant for MDCT scans. Signal-to-noise ratio for phantom water linearly decreased in all FPCT scans with increasing iodine concentrations. Contrast-to-noise ratio curves showed reduced slope at iodine concentrations higher than 75 mg/mL. FPCT arthrography after intra-articular administration of 5 to 6 mL of a 25% dilution of iopromide (Ultravist 300 mg/mL, Bayer HealthCare, Berlin, Germany) was successfully performed in all 4 animal joint specimens. Kappa values for inter-reader agreement of qualitative image analyses were 0.62 to 0.91. Image and depiction quality of 20-s FPCT scans were similar or superior compared with standard MDCT (P < 0.005). Conclusion:FPCT arthrography is feasible and may allow similar image quality compared with standard MDCT arthrography.