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Biomedical subjects

R M Peshock

Publications and source records attributed to R M Peshock.

At least 73 records · Page 4Linked to original sources
PubMed1991

Locomotor system assessment by muscle magnetic resonance imaging.

Clinical evaluation of the locomotor system has long been hampered by difficulty in assessing the morphologic and functional integrity of skeletal muscles. Diagnostic imaging represents a major advance in the diagnosis and management of patients with locomotor dysfunction through the possibility of probing beyond overlying soft tissues to identify muscle lesions, determine their extent, characterize their composition, direct invasive procedures, and monitor therapies. Magnetic resonance imaging (MRI) appears to be the most promising of available imaging methods, because of its great sensitivity to changes in muscle water distribution and fat content. Also, it can distinguish between individual deep and superficial muscles. Serial evaluations of many muscles are practical because of the safety of MRI. While the cost effectiveness in the workup of locomotor dysfunction remains to be determined, the scientific and practical clinical information now available merits further investigation by clinicians and radiologists alike. The purpose of this review is to describe the potential role of skeletal muscle MRI in evaluating the locomotor system.

Humans↗
PubMed1990

Clinical cardiovascular magnetic resonance imaging.

Magnetic resonance imaging (MRI) is a powerful tool providing high-resolution images of the heart and great vessels without the use of ionizing radiation or contrast agents. MRI systems currently in use at many hospitals can be used effectively in the routine, clinical evaluation of many forms of cardiovascular disease, including great vessel disease, ischemic cardiac disease and congenital cardiac disease. Moreover, quantitative and cine MRI techniques are now available, which provide highly accurate measures of chamber size, wall motion and wall thickening. Recent developments in the areas of myocardial tagging, high-speed imaging and MR assessments of flow and perfusion suggest potential for an increasing role of MRI in the clinical evaluation of the cardiovascular system.

Heart Diseases↗
PubMed1989

Magnetic resonance imaging of muscle injury and atrophy in glycolytic myopathies.

Exertional muscle pain, contractures, recurrent rhabdomyolysis, and pigmenturia are common in certain muscle glycolytic disorders. However, the frequency, distribution, and long-term significance of these findings are poorly understood. First we performed magnetic resonance imaging (MRI) of the extremities as a screening test for the detection of muscle abnormalities incurred in activities of daily living in four patients with myophosphorylase deficiency (MPD) and three with muscle phosphofructokinase deficiency (PFKD). MRI findings of abnormal muscles detected upon screening were next compared with changes observed in a prospective study of muscle contractures involving the forearms of four of the patients (two MPD, two PFKD). Screening revealed abnormalities of proximal thigh muscles in three of seven patients, in two of whom (one MPD, one PFKD) a recent history of exertional myalgia coincided with increases in T1 and T2 estimates of isolated thigh muscles. In the third patient (PFKD), focal atrophy of the adductor magnus was present bilaterally. In prospective studies, focal areas of prolonged T1 and T2 appeared in the flexor digitorum superificalis in all four cases and in the flexor digitorum profundus in two cases. Serial imaging suggested that the onset of MRI abnormalities begins within 24 hours of contracture and persists for at least several days and possibly for much longer, with complete recovery apparently the rule. These cases suggests a high prevalence of focal muscle abnormalities in patients with glycolytic myopathies and show the potential of MRI to detect them.

Adolescent↗
PubMed1989

Assessment of myocardial systolic wall thickening using nuclear magnetic resonance imaging.

A quantitative nuclear magnetic resonance (NMR) imaging method of evaluating regional left ventricular function was compared with histochemical evidence of infarction in dogs and functional measurements in patients. Short-axis images of the heart were obtained at end-diastole and at 100 ms intervals thereafter. Regional diastolic left ventricular wall thickness and maximal percent systolic wall thickening were measured at the level of the papillary muscles in each of six segments. In six normal dogs, the mean end-diastolic wall thickness was 9 +/- 1.6 mm, and the mean maximal percent thickening was 61 +/- 11%. In eight dogs with a 4 day old infarct, maximal percent thickening was 5 +/- 8% (p less than 0.001) in the infarcted segments. In 10 normal human volunteers, the mean end-diastolic wall thickness was 10.1 +/- 1 mm, and the mean maximal percent systolic wall thickening was 60 +/- 18%. Reduced maximal percent systolic wall thickening was defined as a value greater than or equal to 2 SD below the mean value obtained in normal volunteers. Seven patients with regional wall motion abnormalities were independently assessed by NMR imaging and biplane ventriculography. With a sensitivity of 94% and a specificity of 80%, NMR imaging demonstrated reduced maximal percent systolic wall thickening in the same segments identified as akinetic or dyskinetic by biplane ventriculography. Thus, abnormalities of regional systolic wall thickening are accurately identified with this quantitative imaging technique.

Adult↗
PubMed1989

In vivo nuclear magnetic resonance imaging of myocardial perfusion using the paramagnetic contrast agent manganese gluconate.

Previous nuclear magnetic resonance (NMR) imaging studies have indicated that coronary occlusion does not produce sufficient changes in standard tissue relaxation times to allow the detection of acute ischemia. To identify acute myocardial perfusion abnormalities, the use of the paramagnetic agent manganese gluconate combined with calcium gluconate (MnGlu/CaGlu) was investigated in canine models of acute coronary artery occlusion. In vitro studies showed that MnGlu/CaGlu was a more efficient relaxing agent than gadolinium-DTPA (relaxivity of 7.8 versus 5.1 s-1 mM-1) and demonstrated affinity for normal myocardium. The distribution of MnGlu/CaGlu as measured by manganese-54 tracer studies was proportional to myocardial blood flow in both normal and ischemic tissue. Hearts excised from dogs after coronary artery occlusion and administration of 0.035 mM/kg MnGlu/CaGlu were imaged ex vivo using a relatively spin-lattice relaxation time (T1)-weighted gradient reversal technique (repetition time [TR] 50 ms and echo time [TE] 9 ms). These images showed increased signal intensity in the normally perfused myocardium with a mean signal intensity ratio of hypoperfused to normal myocardium of 0.55 +/- 0.12 (mean +/- SD). In vivo images obtained in nine dogs after coronary artery occlusion and administration of the same dose of MnGlu/CaGlu demonstrated the region of hypoperfused myocardium in six dogs with a signal intensity ratio of hypoperfused to normal myocardium of 0.64 +/- 0.23 (p less than 0.05 versus control). When a higher dose of 0.1 mM/kg MnGlu/CaGlu was utilized and in vivo imaging was performed using a relatively spin-spin relaxation time (T2)-weighted (TR gated, TE 60 ms) spin-echo sequence in six dogs, the signal intensity of normal myocardium was decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Sports-related muscle injuries: evaluation with MR imaging.

Sports-related muscle pain is frequent in both trained and untrained persons; however, its severity and significance may be difficult to assess clinically. The authors used magnetic resonance (MR) imaging to evaluate acute strains and delayed-onset muscle soreness in sedentary subjects and postmarathon myalgia in trained runners. MR imaging documented the distribution of affected muscles and the absence of focal hematoma, fascial herniation, subsequent fibrosis, and fatty infiltration. Pain associated with strain and that occurring several days after exercise were both associated with prolongation of muscle T1 and T2. In a prospective evaluation of delayed-onset muscle soreness, abnormalities depicted at MR imaging persisted longer than symptoms by up to 3 weeks, indicating that MR imaging is sensitive to tissue alteration that is not apparent clinically. Highly trained marathon runners tended to have relatively mild abnormalities involving the myotendinous junctions.

Athletic Injuries↗
PubMed1989

1989 ARRS Executive Council Award. Exercise-enhanced MR imaging of variations in forearm muscle anatomy and use: importance in MR spectroscopy.

31P MR spectroscopic studies of forearm exercise frequently assume that the volume sampled is appropriate for the muscle of interest and that individual variations in muscle anatomy and use are not important. Postexercise MR imaging was used to assess variations in the size, location, and use of forearm flexors and the accuracy of palpation as a method for locating the muscle of interest. By using the information obtained with MR, the effects of errors in surface-coil position relative to the muscle of interest on 31P MR spectroscopy were examined. In the midforearm of seven men, the greatest diameter of the flexor carpi ulnaris was 29 +/- 4 mm, and that of the flexor digitorum superficialis was 28 +/- 6 mm. However, in the proximal forearm, 58 +/- 10% of the diameter was covered by the palmaris longus, when present (79% of subjects). An unexpected finding was that a focal portion of the superficial finger flexor was used primarily as a wrist flexor in 26% of subjects. Palpation incorrectly identified flexor muscle margins by more than 15 mm in 50% of attempts. When a surface coil was positioned over wrist flexors during handgrip, attenuation of exercise-induced changes in 31P spectra resulted. Exercise-enhanced MR imaging reveals variations in forearm muscle anatomy and use that are common and difficult to appreciate by palpation. It therefore allows improved localization of the sensitive volume for MR spectroscopic studies of muscle physiology.

Adult↗
PubMed1988

Deep venous contribution to hydrostatic blood volume change in the human leg.

The causes of orthostatic intolerance following prolonged bed rest, head-down tilt or exposure to zero gravity are not completely understood. One possible contributing mechanism is increased venous compliance and peripheral venous pooling. The present study attempted to determine what proportion of the increased calf volume during progressive venous occlusion is due to deep venous filling. Deep veins in the leg have little sympathetic innervation and scant vascular smooth muscle, so their compliance may be determined primarily by the surrounding skeletal muscle. If deep veins make a large contribution to total leg venous compliance, then disuse-related changes in skeletal muscle mass and tone could increase leg compliance and lead to decreased orthostatic tolerance. The increase in deep venous volume during progressive venous occlusion at the knee was measured in 6 normal subjects using calf cross-sectional images obtained with magnetic resonance imaging. Conventional plethysmography was used simultaneously to give an independent second measurement of leg volume and monitor the time course of the volume changes. Most of the volume change at all occlusion levels (20, 40, 60, 80 and 100 mm Hg) could be attributed to deep venous filling (90.2% at 40 mm Hg and 50.6% at 100 mm Hg). It is concluded that a large fraction of the calf volume change during venous occlusion is attributable to filling of the deep venous spaces. This finding supports theories postulating an important role for physiological mechanisms controlling skeletal muscle tone during orthostatic stress.

Blood Volume↗
PubMed1988

Left ventricular mass as determined by magnetic resonance imaging in male endurance athletes.

Although many studies of the effect of dynamic exercise training on left ventricular (LV) mass have been reported, controversy continues to exist. Previous work has been criticized because of the techniques used for measuring LV mass, the variable level of training of the subjects recruited and the methods used to normalize the data. In an attempt to resolve this controversy, LV mass was determined using the very accurate and reproducible technique of magnetic resonance imaging (MRI). Highly trained competitive athletes including cross-country skiers, endurance cyclists and long distance runners (VO2max = 77 +/- 1, 72 +/- 2 and 75 +/- 2 ml (kg X min)-1, respectively) were examined. The data were normalized for body weight, body surface area and lean body mass. LV mass was significantly greater in skiers (239 +/- 9 g), runners (244 +/- 10 g) and cyclists (258 +/- 11 g) when compared with nonathletic control subjects (189 +/- 6 g) (p less than 0.001), which represents percent differences of 26, 29 and 37%, respectively. LV mass remained greater in the athletes, regardless of the method used to normalize the data. In addition, there was a good correlation between LV mass and VO2max (r = 0.80, p less than 0.001). It was concluded that LV mass is significantly greater in highly trained competitive endurance athletes and that normalizing LV mass with respect to body weight, body surface area or lean body mass does not alter this relation.

Adult↗
PubMed1988

Gadolinium-DTPA-enhanced nuclear magnetic resonance imaging of reperfused myocardium: identification of the myocardial bed at risk.

Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)-enhanced nuclear magnetic resonance (NMR) imaging can be useful in the identification of reperfused myocardium. However, the effects of dose and the time of administration and the relation of the extent of the region of enhancement to the myocardial bed at risk have not been evaluated. In this study, dogs were given Gd-DTPA (0.1 mM/kg body weight [n = 21] or 0.34 mM/kg [n = 7]) or saline solution (n = 5) after various periods of occlusion and reperfusion. Twenty-five dogs were killed after 1 or 2 h of reperfusion and the excised hearts were imaged. Images were analyzed for presence, intensity and extent of a region of increased signal. All images in dogs given Gd-DTPA had easily identifiable regions of increased signal in the distribution of the reperfused myocardial bed. Analysis of the extent of these regions in spin-echo images of excised hearts when Gd-DTPA was administered after 5 min of reperfusion demonstrated a correlation coefficient of 0.72 with the bed at risk as determined postmortem with a dye perfusion technique. These images consistently overestimated the infarct size. Signal intensity of the reperfused myocardium increased to a maximum of 1.67 times control (p less than 0.05) in spin-lattice relaxation time (T1)-weighted sequences as the dose of Gd-DTPA increased. This was due to a higher concentration of Gd-DTPA in the reperfused myocardium with resultant shortening of the T1 relaxation time. When Gd-DTPA was given after 90 min of reperfusion, NMR images did not identify the bed at risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Estimation of human myocardial mass with MR imaging.

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.

Cadaver↗
PubMed1988

Acute effects of exercise on MR imaging of skeletal muscle in normal volunteers.

Exercise is known to produce changes in the amount and distribution of water in skeletal muscle. Because MR imaging is highly sensitive to changes in water distribution, these changes should be detectable under appropriate imaging conditions. Imaging of the forearms and/or legs was performed in 16 volunteers at 0.35 T, before and after exercise. Exercises included finger flexion and extension, wrist flexion, ankle plantar flexion, and great toe extension. In the case of handgrip exercise, the level of exertion was quantitated. Individual muscles were frequently indistinguishable on preexercise scans. After exercise, active and inactive muscles could be clearly distinguished. For example, in the flexor digitorum profundus, finger flexion resulted in an increase in the image-derived estimate of T1 (T1 postexercise was 1037 +/- 162 msec vs T1 preexercise of 590 +/- 49 msec, p less than .001). T2 also increased (T2 postexercise was 35 +/- 2 msec vs T2 preexercise of 28 +/- 1 msec, p less than .001). Relative spin density also increased (p less than .001). T1, T2, and spin density subsequently decreased with time but were still increased above baseline at 10 min postexercise (p less than .005). Signal changes correlated moderately with the level of exertion (r = .63) and fatigue (r = .45). Vascular occlusion did not prevent intensity changes. Thus, changes in skeletal muscle MR signal intensity occur with exercise and appear to parallel known alterations in water distribution.

Humans↗
PubMed1987

Analysis of spin-echo rephasing with pulsatile flow in 2D FT magnetic resonance imaging.

The effects of pulsatile flow on spin phases in spin-echo magnetic resonance imaging are considered. General expressions for the spin phases of the first four echoes are derived in terms of the Fourier coefficients of flow. These expressions are valid for any time-dependent acceleration and, hence, are not restricted to constant acceleration. The derived expressions are then theoretically evaluated for aortic flow and examined at different points in the cardiac cycle. Our results show that rephasing may occur at certain points in the cardiac cycle for either even or odd echoes depending upon the particular Fourier coefficients of the velocity function and the spin-echo delay time. However, even-echo rephasing is not always necessarily valid. Furthermore, the possibility of determining the flow velocities in the body with an appropriate series of imaging studies is also discussed.

Aorta↗
PubMed1987

Even-echo rephasing and constant velocity flow.

It has been shown previously that for constant magnetic field gradients, constant velocity flow leads to even-echo rephasing for all echo delay times. We show that for flow which is not pluglike, even-echo rephasing also occurs for the pulsed readout gradients used in magnetic resonance imaging if and only if the gradients begin at the time the 90 degrees pulse is applied. We also show for these gradients that even-echo rephasing for all echo delay times in the case of nonpluglike flow implies a constant flow velocity at the point considered. Furthermore, it suffices to assume the vanishing of the spin-echo phase for any even echo, since the vanishing of any even echo for all echo delay times implies that all other even echoes also vanish identically. The odd echoes are then all equal to each other and proportional to the flow velocity. If acceleration is present, it may then be seen that for nonpluglike flow, even-echo rephasing may only be present for some but not all echo delay times. However, for the typical slice selection gradients used in magnetic resonance imaging or for usual readout gradients starting after the 90 degrees pulse is applied, it is shown that for constant velocity flow the even-echo phases do not vanish identically. Hence, rephasing cannot always occur for nonpluglike flow in either of these situations. Furthermore, the spin-echo phases are proportional to the flow velocity.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1987

A general treatment of NMR imaging with chemical shifts and motion.

A general treatment of nuclear magnetic resonance imaging (MRI) and spectroscopic imaging (MRSI), which takes into account the effects of chemical shift, motion, field inhomogeneity, and relaxation times, is presented. A graphical representation based on the k trajectory formalism which includes these effects is then developed for MRI and MRSI acquisition processes. These considerations should be useful in the study and design of flow-sensitive MRI and MRSI methods and the accurate prediction of motion artifacts in conventional MRI and MRSI techniques. We conclude by presenting examples illustrating applications of the general theory to specific MRSI and flow imaging methods.

Fourier Analysis↗
PubMed1987

Nuclear magnetic resonance imaging in Marfan's syndrome.

Detection and evaluation of aortic root and other cardiovascular abnormalities in patients with Marfan's syndrome are important in determining appropriate therapy and preventing premature mortality. To evaluate the role of nuclear magnetic resonance imaging (NMR) in this syndrome, 10 patients were evaluated using a 0.35 tesla commercial nuclear magnetic resonance imaging system. Findings from these studies were compared with data from other noninvasive tests as well as surgical follow-up. Results from these examinations indicate that NMR-derived measurements of aortic root diameter agree closely with echocardiographic measurements. In addition, NMR provides more complete anatomic detail than does echocardiography and can be utilized to assess and follow up virtually all patients with this syndrome.

Adolescent↗
PubMed1986

Detection and localization of recent myocardial infarction by magnetic resonance imaging.

The potential of magnetic resonance imaging (MRI) to detect and localize acute myocardial infarction (AMI) in 27 patients a mean interval of 15 days after AMI was evaluated. Eighteen asymptomatic volunteers were also studied to determine the specificity of the observations. The diagnosis of AMI was established by conventional criteria; the infarct was localized by electrocardiography in all patients, technetium pyrophosphate scintigraphy in 19 and necropsy in 1 patient. MRI detected increased myocardial signal intensity in 88%, cavitary signal in 74% and regional wall thinning in 67% of the patients. At least 1 of these 3 features was seen in the area of the infarct in each patient. The sensitivity of these MRI observations was not influenced by location of the infarct or presence of Q waves. Asymptomatic volunteers also had increased myocardial signal in 83%, cavitary signal in 94% and wall thinning in 11% of cases. Some patients had these findings in myocardial segments not suspected of being involved by recent or remote AMI. It is concluded that AMI can be detected by MRI performed an average of 15 days after infarction. However, the hearts of normal volunteers and apparently normal myocardial segments of patients with AMI may have the MRI findings previously associated with AMI. Of these findings, wall thinning was the most predictive of and specific for AMI.

Adult↗