Gustav Andreisek

MR Neurography: Past, Present, and Future

OBJECTIVE MR neurography (MRN) has increasingly been used in clinical practice for the evaluation of peripheral nerve disease. This article reviews the historic perspective of MRN, the current imaging trends of this modality, and the future directions and applications that have shown potential for improved imaging and diagnostic capabilities. CONCLUSION MRN has come a long way in the past 2 decades. Excellent depiction of 3D nerve anatomy and pathology is currently possible. Further technical developments in diffusion-based nerve and muscle imaging, whole-body MRN, and nerve-specific MR contrast agents will likely play a major role in advancing this novel field and understanding peripheral neuromuscular diseases in the years to come.

Anatomic MR Imaging and Functional Diffusion Tensor Imaging of Peripheral Nerve Tumors and Tumorlike Conditions

In this study 29 patients underwent anatomic and functional imaging (DWI and DTI) of peripheral nerve masses in an attempt to improve their characterization. ADC values were lower in malignant tumors, the involved nerves had lower fractional anisotropy, and DTI showed differences between benign and malignant tumors. The authors concluded that tractography and fractional anisotropy provide insight into neural integrity while low diffusivity indicates malignancy. BACKGROUND AND PURPOSE: A number of benign and malignant peripheral nerve tumor and tumorlike conditions produce similar imaging features on conventional anatomic MR imaging. Functional MR imaging using DTI can increment the diagnostic performance in differentiation of these lesions. Our aim was to evaluate the role of 3T anatomic MR imaging and DTI in the characterization of peripheral nerve tumor and tumorlike conditions. MATERIALS AND METHODS: Twenty-nine patients (13 men, 16 women; mean age, 41 ± 18 years; range, 11–83 years) with a nerve tumor or tumorlike condition (25 benign, 5 malignant) underwent 3T MR imaging by using anatomic (n = 29), functional diffusion, DWI (n = 21), and DTI (n = 24) techniques. Images were evaluated for image quality (3-point scale), ADC of the lesion, tractography, and fractional anisotropy of nerves with interobserver reliability in ADC and FA measurements. RESULTS: No significant differences were observed in age (benign, 40 ± 18 versus malignant, 45 ± 19 years) and sex (benign, male/female = 12:12 versus malignant, male/female = 3:2) (P > .05). All anatomic (29/29, 100%) MR imaging studies received “good” quality; 20/21 (95%) DWI and 21/24 (79%) DTI studies received “good” quality. ADC of benign lesions (1.848 ± 0.40 × 10−3 mm2/s) differed from that of malignant lesions (0.900 ± 0.25 × 10−3 mm2/s, P < .001) with excellent interobserver reliability (ICC = 0.988 [95% CI, 0.976–0.994]). There were no FA or ADC differences between men and women (P > .05). FA of involved nerves was lower than that in contralateral healthy nerves (P < .001) with excellent interobserver reliability (ICC = 0.970 [95% CI, 0.946–0.991]). ADC on DTI and DWI was not statistically different (P > .05), with excellent intermethod reliability (ICC = 0.943 [95% CI, 0.836–0.980]). Tractography differences were observed in benign and malignant lesions. CONCLUSIONS: 3T MR imaging and DTI are valuable methods for anatomic and functional evaluation of peripheral nerve lesions with excellent interobserver reliability. While tractography and low FA provide insight into neural integrity, low diffusivity values indicate malignancy in neural masses.

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.

Soluble Klotho and Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES Fibroblast growth factor 23 (FGF23) levels are elevated in patients with autosomal dominant polycystic kidney disease (ADPKD) and X-linked hypophosphatemia (XLH), but only the latter is characterized by a renal phosphate wasting phenotype. This study explored potential mechanisms underlying resistance to FGF23 in ADPKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS FGF23 and klotho levels were measured, and renal phosphate transport was evaluated by calculating the ratio of the maximum rate of tubular phosphate reabsorption to GFR (TmP/GFR) in 99 ADPKD patients, 32 CKD patients, 12 XLH patients, and 20 healthy volunteers. ADPKD and CKD patients were classified by estimated GFR (CKD stage 1, ≥90 ml/min per 1.73 m(2); CKD stage 2, 60-89 ml/min per 1.73 m(2)). RESULTS ADPKD patients had 50% higher FGF23 levels than did XLH patients; TmP/GFR was near normal in most ADPKD patients and very low in XLH patients. Serum klotho levels were lowest in the ADPKD group, whereas the CKD and XLH groups and volunteers had similar levels. ADPKD patients with an apparent renal phosphate leak had two-fold higher klotho levels than those without. Serum klotho values correlated inversely with cyst volume and kidney growth. CONCLUSIONS Loss of klotho might be a consequence of cyst growth and constrain the phosphaturic effect of FGF23 in most patients with ADPKD. Normal serum klotho levels were associated with normal FGF23 biologic activity in all XLH patients and a minority of ADPKD patients. Loss of klotho and FGF23 increase appear to exceed and precede the changes that can be explained by loss of GFR in patients with ADPKD.

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.

Evaluation of Diffusion Tensor Imaging and Fiber Tractography of the Median Nerve: Preliminary Results on Intrasubject Variability and Precision of Measurements

OBJECTIVE The purposes of this study were to determine the intrasubject side-to-side variability of quantitative and qualitative measures of diffusion tensor imaging (DTI) and fiber tractography of the median nerves and to determine the precision of quantitative measurements and fiber tractography. SUBJECTS AND METHODS Fifteen healthy volunteers (seven men, eight women; mean age, 31.2 years) underwent DTI of both wrists with a single-shot spin-echo-based echo-planar imaging sequence (TR/TE, 7,000/103; b value 1,025 s/mm2). Postprocessing included fiber tractography and quantitative analysis of fiber length, fiber density index, fractional anisotropy, apparent diffusion coefficient, and signal-to-noise ratio. Two readers in consensus graded the quality of fiber tract images of the two wrists as equal, slightly different, or very different. Fiber tractography and all analyses were repeated after 3 weeks, and the images from the two sessions were compared. RESULTS No statistically significant side-to-side differences in quantitative data were found (p=0.054-0.999). In all subjects, the quality of fiber tract images of the right and left median nerves was either slightly or very different. Between the initial and the second quantitative analyses, no statistically significant differences (p=0.086-0.898) were found, and the quality of fiber tract images was rated equal for nine of 15 subjects (60%) and slightly different for six of 15 subjects (40%). CONCLUSION Preliminary results indicate that quantitative evaluation of DTI of the median nerve is precise. The absence of statistically significant intrasubject side-to-side variability in quantitative data suggests that the healthy contralateral nerve can be used as an internal control. Observed side-to-side variability in the quality of fiber tract images, however, rules out side-to-side comparisons in fiber tractography.

3-T High-Resolution MR Neurography of Sciatic Neuropathy

OBJECTIVE The sciatic nerve may normally exhibit mild T2 hyperintensity in MR neurography (MRN) images, rendering assessment of sciatic neuropathy difficult. The purpose of this case-control study was to evaluate whether a quantitative and qualitative analysis of the sciatic nerves and regional skeletal muscles increases the accuracy of MRN in detecting sciatic neuropathy. MATERIALS AND METHODS We retrospectively reviewed the MRN studies of the pelvis and thighs of 34 subjects (12 men and 22 women; mean [± SD] age, 50 ± 15 years), of which 17 had a final diagnosis of sciatic neuropathy according to electrodiagnostic or surgical confirmation, and 17 had no evidence of sciatic neuropathy and served as control subjects. On each side, the sciatic nerves were evaluated for signal intensity (SI), size, course, and fascicular shape, whereas the regional skeletal muscles were evaluated for edema, fatty replacement, and atrophy. In addition, the nerve-to-vessel SI ratio was registered for each side at the same time and 8 months later. RESULTS The sciatic nerves of the abnormal sides exhibited higher nerve-to-vessel SI ratios and higher incidences of T2 hyperintensity, enlargement, and abnormal fascicular shape compared to the nerves of the normal sides. The regional muscles of the abnormal sides demonstrated a higher grade of fatty infiltration and higher frequencies of edema and atrophy. A cutoff value of nerve-to-vessel SI ratio of 0.89 exhibited high sensitivity and specificity in predicting sciatic neuropathy. Calculation of the nerve-to-vessel SI ratio demonstrated excellent inter- and intraobserver reliability. CONCLUSION Both qualitative and quantitative criteria should be used to suggest the MRN diagnosis of sciatic neuropathy.

MR Arthrography of the Shoulder, Hip, and Wrist: Evaluation of Contrast Dynamics and Image Quality with Increasing Injection-to-Imaging Time

OBJECTIVE The purpose of our study was to investigate the contrast dynamics and the relationship between visualization of intraarticular structures and time elapsed between intraarticular injection of contrast agent and MRI in symptomatic patients referred for MR arthrography of the shoulder, hip, and wrist. SUBJECTS AND METHODS Our local ethics committees and the national drug administration approved this multicentric study. We prospectively studied 11 shoulders, 11 hips, and 10 wrists. After the intraarticular gadolinium injection, patients underwent a baseline MR arthrography protocol (time point [TP] 1) and subsequent MRI at another four time points (TP 2-TP 5) up to 240 minutes. The course of contrast-to-noise ratio (CNR) over time was calculated. Three observers assessed the degree of visualization of different intraarticular structures and the overall image quality at each time point using a 3-point scale and a 5-point scale, respectively. RESULTS For all joints, CNR measurements showed peak CNR at TP 1 (21 minutes) and TP 2 (45 minutes) with a subsequent, near-logarithmic decline of CNR values over time. Visualization of different anatomic structures decreased over time. Overall image quality was insufficient for diagnostic purposes at TP 3 (96 minutes) in three (27%) of 11 shoulders and in three (27%) of 11 hips. In two (20%) of 10 wrists, image quality was insufficient at TP 2 (45 minutes). CONCLUSION For MR arthrography, the degree of visualization of intraarticular structures depends on the time elapsed between contrast injection and MRI. MR arthrography of the shoulder and hip should be performed within 90 minutes, and MR arthrography of the wrist should be performed within 45 minutes, after intraarticular injection.

Bisphosphonate-Induced Osteonecrosis of the Jaw: Comparison of Disease Extent on Contrast-Enhanced MR Imaging, [18F] Fluoride PET/CT, and Conebeam CT imaging

BACKGROUND AND PURPOSE: Imaging of bisphosphonate-induced osteonecrosis of the jaw is essential for surgical planning. We compared the extent of BONJ on contrast-enhanced MR imaging, [18F] fluoride PET/CT, and panoramic views derived from standard conebeam CT with clinical pre- and intraoperative examinations. MATERIALS AND METHODS: Between February 2011 and January 2012, ten subjects with written informed consent (9 women; mean, 69.6 years; range, 53–88 years) were included in this prospective ethics-board-approved study. Patients underwent CEMR imaging, [18F] fluoride PET/CT, and CBCT and were clinically examined pre- and intraoperatively. Surgery was performed, and BONJ was histologically confirmed in 9 patients. Location and extent of BONJ on different modalities/examinations were graphically compared (0 = no pathologic finding, 1 = smallest, 5 = largest extent of BONJ). Rank tests were used to assess overall and paired differences of ratings in 9 patients. A P value <.05 was considered statistically significant. RESULTS: Significant differences in BONJ extent among different modalities and examinations were found (P < .001). The highest median rank was seen in PET/CT (4 ± 1.12) and CEMR imaging (4 ± 1.01), followed by intraoperative examinations (3 ± 0.71), CBCT (2 ± 0.33), and preoperative examinations (1 ± 0). No significant differences were found between PET/CT and CEMR imaging (P = .23), except when comparing PET/CT to either CBCT, pre- and intraoperative examinations (all P < .05). Preoperative examinations showed significantly less extensive disease than all other modalities/examinations (all P < .05). CONCLUSIONS: [18F] fluoride PET/CT and CEMR imaging revealed more extensive involvement of BONJ compared with panoramic views from CBCT and clinical examinations.

MR Neurography: Advances

High resolution and high field magnetic resonance neurography (MR neurography, MRN) is shown to have excellent anatomic capability. There have been considerable advances in the technology in the last few years leading to various feasibility studies using different structural and functional imaging approaches in both clinical and research settings. This paper is intended to be a useful seminar for readers who want to gain knowledge of the advancements in the MRN pulse sequences currently used in clinical practice as well as learn about the other techniques on the horizon aimed at better depiction of nerve anatomy, pathology, and potential noninvasive evaluation of nerve degeneration or regeneration.