Evaluation of patients with paramyotonia at 23Na MR imaging during cold-induced weakness

PURPOSE: To prospectively examine whether sodium 23 (23Na) magnetic resonance (MR) imaging can be used to visualize acute intracellular Na+ accumulation and the effects of specific therapy in patients with paramyotonia congenita (PC). MATERIALS AND METHODS: Ethics committee approval and informed consent were obtained. Sixteen patients (four women, 12 men; mean age, 46.7 years +/- 16.7 [standard deviation]) with confirmed PC and 10 healthy volunteers (three women, seven men; mean age, 26.6 years +/- 3) were examined by using a 1.5-T MR system with a 16.8-MHz surface coil. 23Na MR imaging was performed before and after local cooling of the nondominant lower leg and exercising, with experimentally induced weakness scored by a neurologist. The 23Na MR examination was repeated in 13 patients and all volunteers after 3 days and, additionally, in seven patients after 4 days of oral administration of mexiletine, which blocks Na+ channels. The 23Na MR protocol comprised two-dimensional (2D) fast low-angle shot (FLASH), 2D radial, and free induction decay (FID) sequences. The FID data were fitted to a biexponential decay curve to evaluate the slow and fast components of the T2 relaxation time. Fast and slow components were assigned to intra- and extracellular Na+ concentrations, respectively. Radial and FLASH MR images were evaluated by means of a region-of-interest analysis by using 0.3% saline solution for reference. T1- and T2-weighted MR imaging were also performed. Data were analyzed by using a parametric t test. RESULTS: After exercising, all patients developed considerable weakness exclusively in the cooled lower leg; no weakness was observed in volunteers. In patients, all 23Na MR images showed a significant increase in 23Na signal intensity in the cooled lower leg (P < .001) in comparison with nonsignificant findings in volunteers. After treatment with mexiletine, cooling and exercise induced almost no muscle weakness and no changes in 23Na MR signal intensity in patients. CONCLUSION: 23Na MR imaging enables visualization of muscular Na+ accumulation associated with muscle weakness in patients with PC, and effects of specific therapy can be detected.     

Proton and sodium MRI assessment of fluid level in calf tissue

PURPOSE: To investigate the feasibility of using (1)H and (23)Na MRI to detect fluid levels in the lower leg muscle. MATERIALS AND METHODS: Proton and sodium MRI was applied to detect body fluid levels in the lower leg muscles of 18 healthy young male subjects at 3T and 4T. The paradigms under investigation were a postural change from sitting upright to lying supine, and saline infusion. RESULTS: We found that the average proton MR signal in gastrocnemius and soleus muscles were reduced following the postural change by 3.5% +/- 1.4% (P < 0.05) and rose following saline infusion by 3.7% +/- 0.9% (P < 0.01). More dramatically, the sodium MR signal decreased by 7.1% +/- 1.2% (P < 0.01) following the postural change and increased following saline infusion by 12% +/- 3.8% (P < 0.05). The ratio of intra- to extracellular fluid levels was 1.6 +/- 0.5 for the subjects based on the acquired proton and sodium data. CONCLUSION: Our results indicate that proton and sodium MRI can be used to assess fluid levels in the lower extremities, and this technique may be applied to evaluate fluid retention.     

Tissue sodium concentration in human brain tumors as measured with 23Na MR imaging

PURPOSE: To use combined proton (1H) and sodium 23 (23Na) magnetic resonance (MR) imaging to noninvasively quantify total tissue sodium concentration and to determine if concentration is altered in malignant human brain tumors. MATERIALS AND METHODS: Absolute tissue sodium concentration in malignant gliomas was measured on quantitative three-dimensional 23Na MR images with tissue identification from registered 1H MR images. Concentration was determined in gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), and vitreous humor in 20 patients with pathologically proven malignant brain tumors (astrocytoma, n = 17; oligodendroglioma, n = 3) and in nine healthy volunteers. Sodium concentration in tumors and edema was determined from 23Na image signal intensities in regions that were contrast material enhanced on T1-weighted 1H images (tumors) or regions that were only hyperintense on fluid-attenuated inversion recovery (FLAIR) 1H images (edema). Sodium concentrations were measured noninvasively from 23Na images obtained with short echo times (0.4 msec) by using external saline solution phantoms for reference. Differences in mean sodium concentration of all healthy tissue and lesions in patients were tested with a paired t test. Concentration in uninvolved tissues in patients was compared with that in the same tissue types in the volunteers with an independent samples two-tailed t test. RESULTS: Mean concentration (in millimoles per kilogram wet weight) was 61 +/- 8 (SD) for GM, 69 +/- 10 for WM, 135 +/- 10 for CSF, 113 +/- 14 for vitreous humor, 103 +/- 36 for tumor, 68 +/- 11 for unaffected contralateral tissue, and 98 +/- 12 for FLAIR hyperintense regions surrounding tumors. Significant differences (P <.002) in sodium concentration were demonstrated by using a t test for both tumors and surrounding FLAIR hyperintense tissues versus GM, WM, CSF, and contralateral brain tissue. CONCLUSION: 23Na MR imaging with short echo times can be used to quantify absolute tissue sodium concentration in patients with brain tumors and shows increased sodium concentration in tumors relative to that in normal brain structures.     

Effect of exercise on (23)Na MRI and relaxation characteristics of the human calf muscle

The acute affect of voluntary muscle contractions performed by healthy volunteers was evaluated using (23)Na nuclear magnetic resonance (NMR). Three-dimensional gradient-echo (23)Na images, pulse-acquired spectra, and transverse relaxation times were obtained before and after ankle flexion-extension exercise. The muscle sodium concentration was calculated from (23)Na images using a 40 mM NaCl standard and the measured T(2) values. Before exercise the muscle sodium concentration was 26+/-4 mmole/kg wet weight. This agrees closely with literature values, suggesting that muscle Na(+) is fully NMR visible. The (23)Na image intensity increased by 34%+/-7% in the exercised muscle and diminished with a half-life of 30+/-6 minutes. The pulse-acquired spectra, however, did not show any significant change in muscle signal intensity following exercise, but the relative contribution of the slow T(2) component increased. The calculated sodium concentration also did not change significantly after the exercise. We therefore infer that the changes in (23)Na magnetic resonance imaging (MRI) were due to a change in sodium-macromolecular interaction rather than a change in tissue sodium content. We believe that this report represents the first study of (23)Na MRI of skeletal muscle.     

MR imaging in Duchenne muscular dystrophy: Quantification of T1‐weighted signal,contrast uptake,and the effects of exercise

Purpose:

To quantify the differences between normal and corticosteroid‐treated Duchenne muscular dystrophy (DMD) lower limb muscle using signal intensity measurements on T₁‐weighted and gadolinium contrast‐enhanced images and by measurement of muscle T₂ values, and to investigate the effect of exercise.

Materials and Methods:

Eleven ambulant boys with DMD were imaged at 3 Tesla (T₁‐weighted, gadolinium enhancement and T₂ measurement) before stepping exercise and again (gadolinium, T₂ measurement) 4 days later and were compared with five healthy controls imaged 4 days before and after stepping exercise. Muscle region‐of‐interest signal intensities were referenced to external oil and gadolinium phantoms.

Results:

DMD thigh muscle T₂ values were significantly higher than normal values with the exception of the gracilis muscle. Eight of nine muscles studied showed a significant increase in T₁‐w signal intensity in DMD as compared to normal muscle, suggestive of increased fat infiltration in DMD muscle. In the DMD boys, an exercise effect (increased contrast enhancement) was only seen for the tibialis anterior muscle.

Conclusion:

Referenced signal intensity measurements may be used to quantify differences between dystrophic and normal muscle without T₁ mapping. Stepping exercise does not have a large impact on subsequent MR imaging of dystrophic muscle. J. Magn. Reson. Imaging 2009;30:1130–1138. © 2009 Wiley‐Liss, Inc.     

In vivo Na-23 MR imaging and spectroscopy of rat brain during TmDOTP5- infusion.

In vivo sodium-23 and hydrogen-1 magnetic resonance (MR) imaging and spectroscopy of the rat brain during infusion of the shift reagent thulium DOTP5- (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra[methylene phosphonate] was performed to assign the various peaks observed during infusion and to evaluate the shift reagent in discriminating tissue compartments. Na-23 spectra collected during the infusion showed two shifted peaks that were assigned to intravascular Na+ and extracellular muscle Na+, respectively, and one unshifted peak assigned to intra- and extracellular brain Na+ and cerebrospinal fluid Na+. These assignments were validated with H-1 and Na-23 MR imaging and Na-23 chemical shift imaging (CSI). The H-1 and Na-23 images showed that a surface coil placed on a rat head can detect a substantial amount of signal from muscle surrounding the skull. Na-23 CSI spectra from successive 1-mm-thick coronal sections indicated that the shift reagent did not cross the blood-brain barrier. The study also showed that bulk susceptibility shifts are quite small with Tm-DOTP5-. This reagent may be useful in determining compartmental Na+ concentrations and blood flow kinetics in brain and in examining the integrity of the blood-brain barrier.     

3D radial projection technique with ultrashort echo times for sodium MRI: clinical applications in human brain and skeletal muscle.

(23)Na MRI has the potential to noninvasively detect sodium (Na) content changes in vivo. The goal of this study was to implement (23)Na MRI in a clinical setting for neurooncological and muscular imaging. Due to the biexponential T(2) decay of the tissue Na signal with a short component, which ranges between 0.5-8 ms, the measurement of total Na content requires imaging techniques with echo times (TEs) below 0.5 ms. A 3D radial pulse sequence with a TE of 0.2 ms at a spatial resolution of 4 x 4 x 4 mm(3) was developed that allows the acquisition and presentation of Na images on the scanner. This sequence was evaluated in patients with low- and high-grade gliomas, and higher (23)Na MR signals corresponding to an increased Na content were found in the tumor regions. The contrast-to-noise ratio (CNR) between tumor and white matter increased from 0.8 +/- 0.2 to 1.3 +/- 0.3 with tumor grade. In patients with an identified muscular (23)Na channelopathy (Paramyotonia congenita (PC)), induced muscle weakness led to a signal increase of approximately 18% in the (23)Na MR images, which was attributed to intracellular Na(+) accumulation in this region.     

Assessment of myocardial infarction in humans with (23)Na MR imaging: comparison with cine MR imaging and delayed contrast enhancement

PURPOSE: To demonstrate the feasibility of sodium 23 ((23)Na) magnetic resonance (MR) imaging for assessment of subacute and chronic myocardial infarction and compare with cine, late enhancement, and T2-weighted imaging. MATERIALS AND METHODS: Thirty patients underwent MR imaging 8 days +/- 4 (subacute, n = 15) or more than 6 months (chronic, n = 15) after myocardial infarction by using a (23)Na surface coil with a double angulated electrocardiogram-triggered three-dimensional gradient-echo sequence at 1.5 T. In addition, cine, inversion-recovery gradient-echo, and, in the subacute group, T2-weighted images (n = 9) were obtained. Myocardial infarction mass was depicted as elevated signal intensity or wall motion abnormalities and expressed as a percentage of total left ventricular mass for all modalities. Correlations were tested with correlation coefficients. RESULTS: All patients after subacute infarction and 12 of 15 patients with chronic infarction had an area of elevated (23)Na signal intensity that significantly correlated with wall motion abnormalities (subacute; r = 0.96, P <.001, and chronic; r = 0.9, P <.001); three patients had no wall motion abnormalities or elevated (23)Na signal intensity. Only 10 patients in the subacute and nine in the chronic group revealed late enhancement; significant correlation with (23)Na MR imaging occurred only in subacute group (r = 0.68, P <.05). Myocardial edema in subacute infarction correlated (r = 0.71, P <.05) with areas of elevated (23)Na signal intensity but was extensively larger. CONCLUSION: (23)Na MR imaging demonstrates dysfunctional myocardium caused by subacute and chronic myocardial infarction.     

Distribution of Brain Sodium Accumulation Correlates with Disability in Multiple Sclerosis: A Cross-sectional 23Na MR Imaging Study

Purpose: To quantify brain sodium accumulations and characterize for the first time the spatial location of sodium abnormalities at different stages of relapsing-remitting (RR) multiple sclerosis (MS) by using sodium 23 ((23)Na) magnetic resonance (MR) imaging. Materials and Methods: This study was approved by the local committee on ethics, and written informed consent was obtained from all participants. Three-dimensional (23)Na MR imaging data were obtained with a 3.0-T unit in two groups of patients with RR MS-14 with early RR MS (disease duration <5 years) and 12 with advanced RR MS (disease duration >5 years)-and 15 control subjects. Quantitative assessment of total sodium concentration (TSC) levels within compartments (MS lesions, white matter [WM], and gray matter [GM]) as well as statistical mapping analyses of TSC abnormalities were performed. Results: TSC was increased inside demyelinating lesions in both groups of patients, whereas increased TSC was observed in normal-appearing WM and GM only in those with advanced RR MS. In patients, increased TSC inside GM was correlated with disability (as determined with the Expanded Disability Status Scale [EDSS] score; P = .046, corrected) and lesion load at T2-weighted imaging (P = .003, corrected) but not with disease duration (P = .089, corrected). Statistical mapping analysis showed confined TSC increases inside the brainstem, cerebellum, and temporal poles in early RR MS and widespread TSC increases that affected the entire brain in advanced RR MS. EDSS score correlated with TSC increases inside motor networks. Conclusion: TSC accumulation dramatically increases in the advanced stage of RR MS, especially in the normal-appearing brain tissues, concomitant with disability. Brain sodium MR imaging may help monitor the occurrence of tissue injury and disability. ? RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112680/-/DC1.     

Plasma creatine kinase responses of 18- to 30-yr-old African-American men to eccentric exercise

PURPOSE: The primary aim was to describe the response of plasma creatine kinase (CK) activity in a sample of African-American men after a bout of eccentric exercise. The study also described signal intensity changes detected by MR in the musculature of the right lower leg. METHODS: Subjects were 20 male volunteers of African descent (age = 24 +/- 4 [mean +/- SD] yr). Each walked backward for 60 min at 3 km x h(-1) down a 23% grade. Venous blood was sampled before exercise, immediately (0 d) after and 1, 2, 4, and 7 d after exercise for plasma CK assay. Soreness in the plantar flexor muscles was evaluated in 18 subjects at selected times during the 7 d postexercise. Injury to the plantar flexor muscles was evaluated by magnetic resonance imaging (MRI). RESULTS: The subjects had high baseline plasma CK activity (187 +/- 127 IU x L(-1); 163 +/- 70 IU x L(-1) with one outlier excluded) compared with typical clinical norms. As a group, CK activity was increased (P < 0.05) 4 d (980 +/- 1331 IU L(-1)) and 7 d (1022 +/- 1031 IU L(-1)) postexercise, compared with preexercise. Eleven (55%) of the subjects had large, delayed increases in plasma CK activity ("hyperresponses"). As a group, the plasma CK response was similar to responses of comparison Caucasian subjects. All subjects reported delayed muscle soreness; there was no association between soreness and plasma CK. Every subject showed MRI evidence of injury to plantar flexor muscles postexercise but varying in degree and time course. Plasma CK activity correlated to MRI signal intensity (rho = 0.445). CONCLUSION: Results suggest that changes in plasma CK activity and skeletal muscle injury in African-American men after eccentric exercise do not differ from the responses of Caucasians.     

Rapid isotropic 3D‐sodium MRI of the knee joint in vivo at 7T

Purpose

To demonstrate the feasibility of acquiring high‐resolution, isotropic 3D‐sodium magnetic resonance (MR) images of the whole knee joint in vivo at ultrahigh field strength (7.0T) via a 3D‐radial acquisition with ultrashort echo times and clinically acceptable acquisition times.

Materials and Methods

Five healthy controls (four males, one female; mean ± standard deviation [SD] age 28.7 ± 4.8 years) and five patients with osteoarthritis (OA) (three males, two females; mean ± SD age 52.4 ± 5.6 years) underwent ²³Na MRI on a 7T, multinuclei equipped whole‐body scanner. A quadrature ²³Na knee coil and a 3D‐gradient echo (GRE) imaging sequence with a radial acquisition were utilized. Cartilage sodium concentration was measured and compared between the healthy controls and OA patients.

Results

The average signal‐to‐noise ratio (SNR) for different spatial resolutions (1.2–4 mm) varied from ～14–120, respectively. The mean sodium concentration of healthy subjects ranged from ～240 ± 28 mM/L to 280 ± 22 mM/L. However, in OA patients the sodium concentrations were reduced significantly by ～30%–60%, depending on the degree of cartilage degeneration.

Conclusion

The preliminary results suggest that sodium imaging at 7T may be a feasible potential alternative for physiologic OA imaging and clinical diagnosis. J. Magn. Reson. Imaging 2009;30:606–614. © 2009 Wiley‐Liss, Inc.     

Direct relationship between proton T2 and exercise intensity in skeletal muscle MR images

Exercise selectively increases the signal intensities (SI) of active muscles in T2-weighted magnetic resonance (MR) images. If these SI increases are graded with exercise intensity, the identification of muscle recruitment patterns may be possible using MR imaging. The purpose of this study was to determine the effect of force generation during exercise on muscle T2 values. Also, we examined the effects of extracellular fluid volume (ECV) expansion on muscle T2 values. Transaxial midcalf images were collected before and after exercise on eight volunteers in a 1.5T GE magnet using a standard spin echo sequence. Exercise consisted of three consecutive bouts of ankle dorsiflexion against graded loads. Three subjects also underwent brief bouts of lower leg venous occlusion (ECV expansion) during and in addition to the exercise protocol. T2 values for the dorsiflexors significantly increased after exercise. Greater mean force produced during exercise caused greater increases in T2 after exercise (T2 = 29.6 +/- 0.9 X Force). Exercise and venous occlusion caused equivalent increases in muscle cross-sectional area. These equivalent increases in ECV were not accompanied by equivalent increases in muscle T2; venous occlusion alone caused less than a 5% increase in T2 while exercise caused a 14% to 25% increase. Consequently, a direct relationship between increases in T2 and in ECV after exercise was not established. Venous occlusion during exercise, however, did significantly augment the increase in T2 and ECV of the anterior compartment muscles. Contrast enhancement among muscles after exercise in T2-weighted MR images is dependent on generated force during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Magnetic resonance imaging evaluation of muscle usage associated with three exercises for rotator cuff rehabilitation.

PURPOSE: Methods of determining muscle usage for exercises involving rotator cuff muscles are limited. Therefore, this investigation used magnetic resonance imaging (MRI) to evaluate the effect of three different exercises used for rehabilitation of the rotator cuff. METHODS: Five normal volunteer subjects (3 men, 2 women, mean age 31.4 yr) were studied. The exercises were scaption with internal rotation (SIR), military press (MP), and side-lying 45 degrees abduction (SLA). MR imaging was performed immediately before and after exercise using a "fast" spin echo STIR sequence and oblique coronal plane imaging. Changes in signal intensity pre- and post-exercise were measured at comparable section locations for the MR images of the supraspinatus, infraspinatus, teres minor, subscapularis, deltoid, and trapezius. RESULTS: The SLA showed the greatest increase in signal intensity in all the muscles (percent change, P < 0.01) except for the trapezius, which was used more by the MP and SIR. None of the exercises activated the teres minor (percent change, P = not significant). CONCLUSION: These findings have important implications in efficacy of physical rehabilitation of the rotator cuff and avoidance of subacromial impingement exercise motions.     

Muscle infarction in patients with diabetes mellitus: MR imaging findings

PURPOSE: To describe the magnetic resonance (MR) imaging findings in diabetic patients with muscle infarction and to describe commonly associated clinical features. MATERIALS AND METHODS: The MR imaging studies of 21 patients with diabetic muscle infarction were reviewed retrospectively. Of the 21 patients, 12 were women, and nine were men; the mean age was 48 years (range, 30-77 years). RESULTS: Eight patients had bilateral lower-extremity involvement; six had involvement confined to the right lower extremity and seven to the left. The thigh was involved in 17 patients (81%). One or more of the musculi vastus, the most frequently affected muscle group, were affected in 16 patients (76%). Four patients (19%) had isolated calf involvement. MR imaging studies showed diffuse enlargement of involved muscle groups and partial loss of normal fatty intermuscular septa. MR imaging also allowed identification of areas of subfascial fluid in 16 patients (76%) and subcutaneous edema in 19 patients (90%). MR imaging showed involved muscle groups best with T2-weighted, inversion-recovery, and gadolinium-enhanced sequences, where the infarcted muscles appeared diffusely hyperintense compared with adjacent muscles. Comparison of T2-weighted and gadolinium-enhanced MR images of nine patients showed enlarged, enhancing muscles in all patients and small, focal, rim-enhancing fluid collections in six of nine patients (66%). CONCLUSION: Diabetic muscle infarction is suggested in diabetic patients with sudden onset of severe pain in the thigh or calf muscles who have MR imaging findings of diffuse edema and swelling of multiple thigh and calf muscles (often in more than one compartment).     

Fatty atrophy of supraspinatus and infraspinatus muscles: accuracy of US

PURPOSE: To prospectively evaluate the accuracy of ultrasonography (US) in depicting fatty atrophy of the supraspinatus (SSP) and infraspinatus (ISP) muscles, with magnetic resonance (MR) imaging as the reference standard. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. SSP and ISP muscles of 65 consecutive patients (27 women, 38 men; mean age, 53.1 years; range, 28-83 years) with possible rotator cuff tears were evaluated with US in two planes. Visibility of muscle contour, pennate pattern, the central tendon, and muscle echogenicity was assessed by two radiologists. On the basis of these findings, diagnosis of substantial fatty atrophy was made at US. Accuracy, sensitivity, specificity, proportion of over- and underestimations, and interobserver agreement in diagnosis of substantial (grade 2 or greater) muscle atrophy were determined. Fatty atrophy was graded at MR imaging as follows: score of 0 = no intramuscular fat, score of 1 = some fatty streaks, score of 2 = fat evident but less extensive than muscle, score of 3 = fat equal to muscle, and score of 4 = fat more extensive than muscle. RESULTS: For readers 1 and 2, the accuracy of US in depicting fatty atrophy of SSP muscle was 75% (49 of 65) and 72% (47 of 65), sensitivity was 89% (eight of nine) and 100% (nine of nine), and specificity was 73% (41 of 56) and 68% (38 of 56), respectively. For readers 1 and 2, the accuracy of US in depicting fatty atrophy of ISP muscle was 85% (55 of 65) and 80% (52 of 65), sensitivity was 58% (11 of 19) and 63% (12 of 19), and specificity was 96% (44 of 46) and 87% (40 of 46), respectively. Overestimation of SSP muscle atrophy was more common (23% [15 of 65] for reader 1 and 28% [18 of 65] for reader 2) than underestimation (2% [one of 65] for reader 1 and 0% [0 of 65] for reader 2). For readers 1 and 2, overestimation of ISP muscle atrophy was 3% (two of 65) and 9% (six of 65) and underestimation was 12% (eight of 65) and 9% (seven of 65), respectively. Interobserver agreement was moderate for SSP (kappa = 0.55) and substantial for ISP (kappa = 0.71) muscles. CONCLUSION: US is moderately accurate in the diagnosis of substantial fatty atrophy of the SSP or ISP muscle.     

Visualizing muscle activation by fusing fast MR images

The purpose of this study was to conduct fast-acquired muscle functional magnetic resonance imaging (fast-mfMRI). Fast-mfMRI is a method of fusing fast MR images in order to visualize muscle activity. Exercise selectively increases the signal intensities (SI) of active muscles in T2-weighted magnetic resonance (MR) images. A fast-mfMRI image is a fusion of two types of images: an anatomic image acquired by the TrueFISP method and a functional image acquired by the SE-EPI (spin-echo echo-planar-imaging) method. MR images of four healthy males were recorded at rest before and after plantar flexion. The Gain of the MR signal remained constant from before the flexion exercise (at rest) to after the exercise. The data on the area of muscle activity could be extracted by adapting a threshold value obtained by a functional image at rest to the functional image after the exercise. By uniting the data on the area of muscle activity with the anatomic images after the exercise, we constructed a fused image rich in anatomical information and effective in visualizing muscle activity. These fast-mfMRI images can be acquired in 14 seconds. Our results suggest that fast-mfMRI has the potential to measure muscle activity in the trunk, where conventional mfMRI has been ineffective.     

Accuracy of abnormal paraspinal muscle findings on contrast-enhanced MR images as indirect signs of unilateral cervical root-avulsion injury

PURPOSE: To evaluate the accuracy of abnormal magnetic resonance (MR) findings in the paraspinal muscles as indirect signs of nerve-root avulsion injury. MATERIALS AND METHODS: Forty-three consecutive patients suspected of having unilateral root-avulsion injury underwent MR imaging and were evaluated. Paraspinal muscles were evaluated for abnormal signal intensity on T1- and T2-weighted images, abnormal enhancement on images obtained after contrast material enhancement, and muscle volume loss. MR images were interpreted independently by two observers for interobserver variability. MR findings were compared with findings of root continuity, determined with a combination of surgery and clinical evaluation. Sensitivities, specificities, and kappa values of the findings were calculated. RESULTS: Sensitivities of MR findings in the paraspinal muscles indicating root-avulsion injury were 88% (36 of 41 patients) for abnormal enhancement, 83% (34 of 41 patients) for high signal intensity on T2-weighted images, 37% (15 of 41 patients) for high signal intensity on T1-weighted images, and 71% (29 of 41 patients) for muscle volume loss. Specificities for all findings were 100% (two of two patients). Of the paraspinal muscles, findings in the multifidus muscle were the most accurate and provided the highest interobserver agreement (kappa = 0.81). CONCLUSION: Contrast material-enhanced abnormal MR findings in the paraspinal muscles are accurate in indicating root-avulsion injuries, and abnormal enhancement in the multifidus muscle is the most accurate among paraspinal muscle findings.     

Acute rhabdomyolysis: evaluation with magnetic resonance imaging compared with computed tomography and ultrasonography

Fifteen patients with acute rhabdomyolysis were evaluated with low field magnetic resonance (MR) imaging and the results compared with those obtained using computed tomography (CT) and ultrasonography (US). With MR imaging, abnormal muscles with areas of increased signal intensity were seen in every patient, which probably reflects increased water content or increased mobility of water molecules caused by inflammatory reaction and oedema in the injured and necrotic muscles. Computed tomography without intravenous contrast medium demonstrated abnormal muscles in most patients examined with this modality. The CT findings consisted of areas of focal hypodensity in muscles. With US, abnormal muscles were seen in less than half of the patients studied. The normal structure of striated muscle was focally disturbed and areas of both decreased and increased echogenicity were found. Magnetic resonance imaging had a higher sensitivity in the detection of abnormal muscles than CT or US (100%, 62% and 42%, respectively). The findings of all these modalities are non-specific, but together with the clinical and laboratory data they confirm the diagnosis of rhabdomyolysis. The information gained from imaging studies is useful in the assessment of the extent and distribution of rhabdomyolysis. The precise identification of affected muscle compartments by MR imaging is valuable when surgical fasciotomy is considered for treatment; the procedure can then be appropriately directed to the compartments with clearly abnormal muscles.     

Pisotriquetral joint: assessment with MR imaging and MR arthrography

PURPOSE: To evaluate magnetic resonance (MR) imaging and MR arthrographic findings in the pisotriquetral joint (PTJ) and their contribution to assessment of PTJ osteoarthritis. MATERIALS AND METHODS: Images of 22 fresh human cadaveric PTJs were obtained with both conventional and arthrographic MR techniques. The MR appearances of all intraarticular and periarticular structures were analyzed and correlated with anatomic slices. Two readers graded visibility of anatomic structures and severity of joint abnormalities. Differences in the visibility ratings at standard MR imaging and at MR arthrography were calculated. Association between the type of pisiform insertion of ligament or muscle with cartilaginous abnormalities of the PTJ was assessed. The association between cartilaginous lesions and osteoarthritic changes was calculated. RESULTS: The tendon sheath, the fibrous capsule, and cartilaginous surfaces were better visualized at MR arthrography than at MR imaging. Pisohamate and pisometacarpal ligaments were slightly better seen on MR arthrograms. Tendons, muscles, and retinacular structures were well demonstrated at both conventional MR and MR arthrography. Cartilaginous lesions and osteophytes were easily identified and were detected more often in the pisiform bone than in the triquetral bone. Communication of the PTJ with the radiocarpal joint was noted in 18 (82%) of 22 wrists. CONCLUSION: MR imaging and/or MR arthrography allows visualization of all anatomic structures of the PTJ. MR arthrography improves visualization of findings of osteoarthritis.     

Measuring human cardiac tissue sodium concentrations using surface coils, adiabatic excitation, and twisted projection imaging with minimal T2 losses

PURPOSE: To measure tissue sodium concentrations in the human heart with (23)Na MRI using a surface coil, thereby eliminating the effects of inhomogeneous excitation by surface coils and minimizing T(1) and T(2) relaxation. MATERIALS AND METHODS: We combined fully relaxed, very short-echo, (23)Na twisted projection imaging (TPI) with adiabatic half passage (AHP) excitation and external referencing on subjects and comparing with a concentration reference phantom scan to quantify TSC with surface coils. (23)Na signal losses during hard (square), composite, and tanh/tan amplitude/frequency-modulated AHP excitation pulses were analyzed over a wide range of RF field strengths and T(2short) values. RESULTS: AHP excitation yielded a homogeneous excitation flip angle and negligible losses compared to a 90 degrees hard pulse wherever the B1 field exceeded the adiabatic threshold, rendering this sequence suitable for applications that use surface coil excitation. An AHP (23)Na TPI sequence was used with a surface coil at 1.5 T to noninvasively quantify myocardial TSC in 10 normal volunteers. The mean TSC was 43 +/- 4, 53 +/- 12, and 17 +/- 4 micromol/g in the left ventricular (LV) free wall, septum, and adipose tissue, respectively, consistent with prior invasive measurements on biopsy and autopsy specimens. CONCLUSION: It is now possible to noninvasively quantify TSC in the human heart with surface coil (23)Na MRI.