No abstract

Because determination of neurologic integrity after severe limb trauma is crucial in patient care, the authors assessed magnetic resonance (MR) imaging as a tool to map denervated motor units of skeletal muscle in patients with traumatic peripheral neuropathy. Denervation was confirmed in 22 patients with use of electromyography, surgery, or both. MR imaging was performed with moderately T1- and T2-weighted spin-echo and short-tau inversion-recovery (STIR) sequences. MR imaging was unreliable in depicting acute denervation. Muscles of patients with subacute denervation had prolonged T1 and T2, which contributed to conspicuous hyperintensity on STIR images. Chronically denervated muscles showed marked atrophy, variable changes on STIR images, and conspicuous fatty infiltration on T1-weighted images. Normal variants in motor unit anatomy were seen in denervated muscle volumes outside the expected distribution of the injured nerve. MR imaging is promising for the noninvasive mapping and monitoring of denervated muscle in subacute and chronic phases of peripheral neuropathy.

1-123 metaiodobenzylguanidine (MIBG) is a new radiopharmaceutical with properties that allow the characterization of the sympathetic innervation of several organ systems. In this study, we used MIBG with tomographic imaging to evaluate noninvasively the differences in myocardial sympathetic innervation in 14 healthy volunteers and 16 patients with severe dilated cardiomyopathy (CM). Initial (15-minute) images demonstrated no significant differences in MIBG concentration in the hearts of patients with CM and of healthy volunteers. However, the myocardial retention of MIBG was significantly reduced in the patients with CM. Expressed as the percent washout from 15 to 85 minutes, the patients with CM had a 28 ± 12% washout rate compared with 6 8% in the controls (p

SUMMARY Left ventricular (LV) performance at rest and during multilevel exercise in the supine and upright positions was studied in seven normal subjects with equilibrium radionuclide ventriculography. The mean left ventricular end-diastolic volume (LVEDV) during supine rest was 107 4 10 ml (± SEM) and 85 ± 6 ml (p < 0.02) in the upright position; the mean resting left ventricular end-systolic volumes (LVESV) were not diSferent in the upright and supine positions. The Changes in posture at rest are associated with significant changes in LV filling and stroke volume. A transition from the supine to the upright position produces a decrease in LV end-diastolic pressure1-3 and volume4-6 and in stroke volume.' -4 6-10 The results of previous studies of the alterations in LV enddiastolic volume during exercise in the supine position have varied.5, 6, 11-15 There is general agreement that end-systolic volume is smaller during exercise than at rest;6 11, 12, 14,15 most investigators3' 6, 12, 13 have reported an exercise-induced increase in stroke volume, although others have not.1 4These data are generally consistent with an enhanced contractile state From the Departments of Medicine

The accuracy and reproducibility of magnetic resonance (MR) imaging in the determination of left ventricular mass in humans was investigated. Left ventricular wall volume was measured from ten short-axis, end-diastolic MR images that spanned the left ventricle. Mass was estimated on the basis of average left ventricular wall volume and an assumed myocardial density. To establish the accuracy of the technique, the authors imaged ten cadaver hearts and compared true left ventricular weight with the mass estimate based on MR imaging findings. In vivo determination of left ventricular mass was evaluated in 40 subjects, with resultant calculated masses of 156.4-319.3 g. Intra- and interobserver variabilities of the technique were analyzed in ten subjects. Both the intra- (r = .96, standard error of estimate [SEE] = 11.1 g) and interobserver variabilities (r = .91, SEE = 17.8 g) were excellent. Eight subjects were imaged on two separate occasions to evaluate reproducibility of the technique and confidence limits for a given measurement. For these eight, there was good correlation between the two estimates (r = .93, SEE = 21 g). The authors conclude that MR imaging yields highly accurate and reproducible estimates of left ventricular mass in humans in vivo.