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Biomedical subjects

R M Peshock

Publications and source records attributed to R M Peshock.

At least 55 records · Page 3Linked to original sources
PubMed1993

Denervated human skeletal muscle: MR imaging evaluation.

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.

Extremities↗
PubMed1993

Muscle proton T2 relaxation times and work during repetitive maximal voluntary exercise.

We studied the effects of progressive maximal voluntary handgrip contractions (MVCs) on muscle proton spin-spin (T2) relaxation times and work, measured as the integrated force vs. time curve (FTI). Six healthy volunteers performed 10, 20, 40, and 80 MVCs in a 0.35-T magnet on four separate occasions. Repeated measures analyses of variance of increases in T2 and FTI during successive bouts were significant (P < 0.005 and P < 0.001, respectively). FTI increased with successive bouts to a greater extent than did muscle T2 (P < 0.05). For T2, the Helmert contrast judged the 10-MVC response lower than the mean of the remaining responses (P < 0.005), and the differences between all others compared with the means of subsequent responses were not significant, indicating a "flattening" of the T2 response after the increase from 10 to 20 repetitions. For FTI, all the single degree of freedom Helmert contrasts were significant (P < 0.001), indicating a continual increase in response over increased MVCs. The curved nature of the T2 response conformed best to a hyperbolic function, suggesting that a limit of approximately 32% exists for the change in T2 during progressively longer bouts of MVCs. A limit in the T2 response is consistent with the existence of a limit in the amount of water that muscle can take up from the vasculature during exertion.

Adult↗
PubMed1993

Respiratory muscle limitation in patients after pneumonectomy.

Exercise capacity is significantly impaired in postpneumonectomy patients who have relatively normal remaining lungs. Our objectives are to determine (1) the nature and extent of mechanical ventilatory abnormalities and oxygen cost of breathing in such patients, and (2) the efficacy of a selective respiratory muscle training program in improving ventilatory and exercise performance. A group of eight postpneumonectomy and eight normal subjects (mean ages 59 and 50 yr, respectively) were studied during steady-state exercise and resting voluntary hyperventilation. Ventilation, work of breathing, cardiac output, and oxygen costs of breathing were determined. Four postpneumonectomy and five normal subjects were studied before and after a respiratory muscle training program. In patients after pneumonectomy compared with normal control subjects, maximal oxygen uptake (VO2) was 56% lower (p < 0.001). Work of breathing was significantly higher at a given ventilation. Mechanical efficiency of ventilation was lower by 44% (p < 0.05). Near maximal VO2, 48% of any additional increment of total-body VO2 was required to sustain the associated increment in ventilatory work, compared with 28% in normal subjects (p < 0.05), suggesting that competition between respiratory and nonrespiratory muscles for oxygen delivery is a significant factor limiting exercise after pneumonectomy. After respiratory muscle training, maximal respiratory pressures improved but maximal sustained ventilation and maximal VO2 did not improve significantly, suggesting that selective respiratory muscle training is of limited utility in postpneumonectomy patients.

Analysis of Variance↗
PubMed1992

Left ventricular dimensions and mass using magnetic resonance imaging in female endurance athletes.

Few published studies of left ventricular (LV) mass in female endurance athletes have been performed with M-mode echocardiography, which involves assumptions of LV geometry. Therefore, magnetic resonance imaging, a 3-dimensional technique, was used to examine LV mass, LV end-diastolic volume and mean wall thickness in female long distance runners (n = 13; mean age 29 years), cyclists (n = 12; mean age 26 years) and cross-country skiers (n = 11; mean age 24 years), and the findings were compared with sedentary control subjects (n = 10; mean age 27 years) matched for height and body weight. The physical characteristics for all subjects included height (mean 166 cm, and body weight (mean 56 kg). The percent body fat (mean 11.7) and maximal oxygen uptake (VO2max, mean 63 ml.kg-1.min-1) were similar (p greater than 0.05) among all athletic groups, but significantly different from the control group (body fat, mean 22.5%; VO2max, mean 35 ml.kg-1.min-1). LV mass (mean 159 kg), LV end-diastolic volume (mean 122 ml), and mean wall thickness (mean 11.5 mm) were also similar among the athletic groups and significantly larger than the following control values: LV mass (mean 115 g), LV end-diastolic volume (mean 93 ml) and mean wall thickness (mean 9.8 mm). Ratios of LV mass to lean body weight were similar among all athletic groups, although athletic groups had larger ratios (p less than 0.05) than the sedentary control subjects. LV mass/LV end-diastolic volume ratio was similar (p greater than 0.05) among all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

The skeleton in congenital, generalized lipodystrophy: evaluation using whole-body radiographic surveys, magnetic resonance imaging and technetium-99m bone scintigraphy.

Congenital generalized lipodystrophy (CGL) is a rare genetic disease characterized by the absence of body fat from birth. Focal bone lesions have also been reported, but their pathophysiology is poorly understood. To characterize skeletal abnormalities further in 3 patients with CGL, we employed whole-body radiographic skeletal surveys, magnetic resonance imaging (MRI, including gadolinium enhancement), and triple phase technetium-99m methylene diphosphonate bone scintigraphy. Radiographs showed numerous focal lesions within the long bones, as described in other reports. MRI showed that the entire marrow space of the long bones was abnormal and was characterized, at least in part, by the absence of marrow fat. Prolonged T1 and T2 times and marked gadolinium enhancement were observed in radiographically normal-appearing long bone. Radiographically lytic lesions occasionally demonstrated fluid-fluid levels on MRI and enhanced peripherally after gadolinium infusion. Bone scintigraphy findings such as periarticular hyperemia were relative subtle. We conclude that the appendicular skeleton of patients with CGL is diffusely abnormal and is predisposed to focal osteolysis and cyst formation.

Adult↗
PubMed1992

MR imaging-guided muscle biopsy for correlation of increased signal intensity with ultrastructural change and delayed-onset muscle soreness after exercise.

To determine if there is a correlation between the degree of delayed increase in signal intensity (SI) of muscle after exercise on magnetic resonance (MR) images and the amount of ultrastructural (ULS) injury and delayed-onset muscle soreness (DOMS), MR imaging-guided muscle biopsy was performed to obtain tissue from the legs of nine sedentary subjects 48 hours after downhill running on a treadmill. The degree of soreness was subjectively graded. T1-weighted, spin-density, T2-weighted, and short inversion time inversion-recovery images were obtained before and after biopsy, at 48 and 96 hours after exercise, respectively. The delayed SI increase of muscle on images obtained before biopsy was subjectively graded and measured. The degree of ULS injury was determined with electron micrographs. Serum creatine kinase levels were obtained before and up to 144 hours after exercise at 24-hour intervals. The measured SI, SI grades, and DOMS grades were correlated with the degree of ULS injury. Linear regression analysis revealed poor correlation between the DOMS grades and the degree of ULS injury and good correlation between the SI grade and the degree of ULS injury.

Adult↗
PubMed1992

Finger-specific flexor recruitment in humans: depiction by exercise-enhanced MRI.

To evaluate the spatial distribution of human forearm musculature stressed by finger-specific exercise, magnetic resonance imaging was performed in conjunction with exercise protocols designed to separately stress the flexor digitorum superficialis and flexor digitorum profundus. These muscles were shown to consist of subvolumes selectively recruited by flexion of the individual fingers. Knowledge of the finger-specific regions of muscle recruitment during finger flexion could improve sampling accuracy in electromyography, biopsy, magnetic resonance spectroscopy, and invasive vascular sampling studies of hand exercise.

Adult↗
PubMed1992

Peculiar distribution of adipose tissue in patients with congenital generalized lipodystrophy.

Congenital generalized lipodystrophy (CGL) is a rare genetic disease with extreme paucity of fat from birth which is believed to be generalized, involving the whole body. Affected patients are characterized by severe insulin resistance. Sites of adipose tissue distribution in patients with CGL have not been studied systematically. Therefore, the fat distribution in three women (17-20 yr old) with CGL was investigated. Determination of body composition by underwater volume displacement suggested the complete absence of body fat (range, -3 to -7%; normal, 15-25%). Whole body magnetic resonance imaging, however, detected fat in particular anatomical sites, namely in orbits, palms and soles, and periarticular and epidural regions. Some fat was also localized in the tongue, breasts, vulva, and buccal area. Fat in other subcutaneous areas, intraabdominal and intrathoracic regions, and bone marrow was essentially absent. Thus, patients with CGL do not have a complete absence of body fat; of interest, fat is present in those sites where adipose tissue may be serving mainly a mechanical function. Patients with CGL, therefore, provided a unique opportunity to identify the various sites of localization of "mechanical" adipose tissue in the human body. Our study suggests that the genetic defect in CGL results in poor growth and development of metabolically active adipose tissue, whereas mechanical adipose tissue is well preserved.

Adipose Tissue↗
PubMed1991

Automated localization and identification of lower spinal anatomy in magnetic resonance images.

Clinical interpretation of the subtle changes present in MR images in the setting of disease currently relies on subjective image analysis. Image evaluation could potentially be improved by computerized segmentation and precise quantification of the image anatomy. However, this cannot be automated unless reliable navigation within an image is established, capable of compensating for unpredictable factors such as anatomical variability, positioning of an image plane in the body, and variable image characteristics. Focusing on the lower spinal region, this paper explores the presence of image- and anatomy-invariant features which facilitate automated, unconstrained identification, and localization of basic lower spine anatomy.

Algorithms↗
PubMed1991

Contrast-enhanced magnetic resonance imaging of hypoperfused myocardium.

Contrast-enhanced magnetic resonance (MR) imaging can define myocardial perfusion defects due to acute coronary occlusion. However, since most clinically important diagnostic examinations involve coronary arteries with subtotal stenoses, we investigated the ability of MR imaging with a manganese contrast agent to detect perfusion abnormalities in a canine model of partial coronary artery stenosis. The contrast agent was administered after the creation of a partial coronary artery stenosis with the addition of the coronary vasodilator dipyridamole in six of 12 animals. The hearts were imaged ex situ using gradient reversal and spin-echo sequences, and images were analyzed to determine differences in signal intensity between hypoperfused and normally perfused myocardium. Comparison of MR images with regional blood flow and thallium-201 measurements showed good concordance of hypoperfused segments in those animals given dipyridamole, with 75% of the abnormal segments correctly identified. In those animals not given dipyridamole, 48% of segments were correctly identified. Thus, ex vivo MR imaging with a paramagnetic contrast enhancement can be used to detect acute regional myocardial perfusion abnormalities due to severe partial coronary artery stenoses.

Animals↗
PubMed1991

Fast short-tau inversion-recovery MR imaging.

To enhance the versatility of the short-tau inversion-recovery (STIR) sequences, the authors determined a range of repetition time (TR) and inversion time (TI) combinations that suppress signal intensity from fat by study of both patient and phantom images. To make fast STIR images, variations in the following pulsing conditions were studied with use of an interactive computer program: decreasing the TR, limiting the number of excitations, and limiting the number of phase-encoding steps. The authors found that (a) STIR imaging need not be time consuming, (b) fat suppression can be accomplished at shorter TR by using shorter TI, and (c) short-TR fast STIR imaging is sensitive to enhancement with gadopentetate dimeglumine.

Humans↗
PubMed1991

Spatial and temporal registration of cardiac SPECT and MR images: methods and evaluation.

Image registration may assist in the integration of information from multiple sources by allowing direct point-for-point comparisons of studies. To determine the usefulness of such a technique, a method for the spatial and temporal registration of four-dimensional single photon emission computed tomographic (SPECT) and magnetic resonance (MR) cardiac images was developed. Automatically detected left ventricular endocardial surfaces were used to determine the best transform between the two sets of surface points, and that transform was applied to the original SPECT image. A fused image created from the MR and the transformed SPECT images combined the information in both. The authors tested the method with seven patient studies. Registration reduced the distance between the MR and SPECT left ventricular endocardial surfaces by 30%, to an average of 2.7 mm. The authors found that, by using the fused images, perfusion abnormalities could be easily localized and correlated to high-resolution endocardial wall motion and systolic wall thickening.

Coronary Disease↗
PubMed1991

Osteomyelitis: characteristics and pitfalls of diagnosis with MR imaging.

Prospective and retrospective magnetic resonance (MR) imaging (0.35-T) interpretations were compared with final diagnoses in 110 patients suspected to have osteomyelitis. Diagnostic criteria of dark marrow on T1-weighted images and bright marrow on short-tau inversion-recovery images yielded a prospective sensitivity of 98% and a prospective specificity of 75%. Sixty percent of uncomplicated septic joint effusions demonstrated abnormal marrow signal intensity that was mistaken for osteomyelitis. Retrospective review revealed that overall specificity could be improved to 82% without loss of sensitivity if increased marrow signal intensity on T2-weighted images were included as an additional criterion. Specificity may be further increased by use of knowledge of morphologic patterns that distinguish various forms of osteomyelitis. Ten patients (9%) had potential pitfall diagnoses (eg, fracture, infarction, healed infection) that mimic osteomyelitis. MR imaging can be sensitive and specific for osteomyelitis if characteristic appearances and pitfall diagnoses are incorporated into the diagnostic criteria.

Acute Disease↗
PubMed1991

Absence of exercise-induced MRI enhancement of skeletal muscle in McArdle's disease.

To assess the role of glycogenolysis in mediating exercise-induced increases in muscle water as monitored by changes in muscle proton relaxation times on magnetic resonance imaging (MRI) and cross-sectional area (CSA), five patients with myophosphorylase deficiency (MPD) were compared with seven controls. Absolute and relative work loads were matched during ischemic handgrip and graded cycling, respectively. Relaxation times of active muscle did not increase after handgrip in MPD (T1: 1 +/- 14%, P greater than 0.1; T2: 4 +/- 4%, P greater than 0.1) but did in controls (T1: 59 +/- 30%, P less than 0.005; T2: 26 +/- 9%, P less than 0.005). The volume of exercised muscles, estimated by CSA, increased in both groups after handgrip (controls: 13.8 +/- 3.5%, n = 7, P less than 0.0001; MPD: 7.5 +/- 1.5%, n = 4, P less than 0.005), but the change was greater in controls (P less than 0.02). Ischemic handgrip in controls resulted in a large increase in finger flexor signal intensity (SI) on short tau-inversion recovery images (25 +/- 7%, n = 3; P less than 0.005 compared with preexercise) and a further increase with subsequent reflow (43 +/- 11%, n = 3; P less than 0.001 compared with rest); in MPD, SI did not increase. The ratio of active to inactive muscle SI did not increase from rest to maximal cycle exercise in MPD (0 +/- 20%, n = 2, P greater than 0.1) but did in normals (73 +/- 36%, n = 3; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Three-dimensional motion and perfusion quantification in gated single-photon emission computed tomograms.

Methods for quantification and display of left ventricular (LV) functional parameters from gated single-photon emission computed tomographs are described. Using previously documented surface detection methods, we developed techniques for calculating global variables, such as volumes and areas, as well as local variables such as segmental motion and local perfusion from gated tomographic radionuclide ventriculograms (TRVG) and gated perfusion tomograms (sestamibi). We have developed three-dimensional displays to allow realistic visualizations of the results. The motion results have been validated using correlative magnetic resonance imaging (MRI) studies; motion calculated from user-traced MR images of the heart was compared to motion calculated from automatically detected surfaces in TRVG and sestamibi. The average motion error was calculated to be 0.67 mm in TRVG and -0.21 mm in sestamibi. Errors were largest in basal LV regions; we explain this phenomenon using simulations. Finally, we present additional examples of the analysis using studies obtained from normal volunteers and from subjects whose coronary artery anatomies were known.

Coronary Disease↗