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J L Fleckenstein

Publications and source records attributed to J L Fleckenstein.

63 records · Page 4Linked to original sources
PubMedDate not supplied

Effect of perfusion on exercised muscle: MR imaging evaluation.

An ischemic clamp model of exercise was used to evaluate the potential role of blood flow in mediating changes in the magnetic resonance imaging appearance of skeletal muscle. Proton relaxation times of muscle were serially estimated in 10 healthy subjects (a) before exercise, (b) after exercise in the presence of vascular occlusion (VO1), (c) during vascular reocclusion after 1 minute of reperfusion (VO2), and (d) after reinstitution of continuous flow. T1 and T2 of active muscles were increased during VO1. During VO2, there were additional increases in relaxation times of active muscles. Reinstitution of continuous flow was associated with a continuous decrease in the T2 of exercised muscle. Hence, blood flow was not required for increases in T1 and T2 with exercise. Additional relaxation time increases occurred after a brief period of reperfusion; however, continuous flow was associated with a decrease in T2.

Adult↗
PubMedDate not supplied

Three-dimensional reconstruction of skeletal muscle from MRI.

Three-dimensional (3D) reconstructions of medical images can provide useful information to the radiologist, enabling delineation and spatial correlation of anatomic structures in one image rather than consecutive two-dimensional (2D) images. Magnetic resonance imaging (MRI) is known to be a powerful technique for evaluation of skeletal muscle pathology and physiology. We investigated the role of 3D reconstruction from MRI images of pathological and healthy muscle, using volume rendering. The ability to easily delineate and recognize normal and injured muscle in the 3D images were dependent upon the original contrast between normal and injured muscle, spatial resolution, and anatomic complexity in the original slices, and also on imaging parameters such as volume averaging.

Algorithms↗
PubMedDate not supplied

Preretinal neovascularization in diabetic retinopathy: a preliminary investigation using contrast-enhanced magnetic resonance imaging.

Preretinal neovascularization is a well-described feature of advanced diabetic retinopathy. In this study, contrast-enhanced magnetic resonance imaging was used to examine blood-retinal barrier breakdown associated with preretinal neovascularization in three subjects with proliferative diabetic retinopathy. Using a standard imaging protocol, a varying degree of vitreous enhancement was observed in these eyes. The location and severity of enhancement, judged by visual inspection of the images, corresponded to the fluorescein angiographic and/or clinical appearance of preretinal neovascularization. This result suggests that contrast-enhanced magnetic resonance imaging may prove a reasonable approach to the identification of preretinal neovascularization in eyes with significant media opacities.

Adult↗
PubMedDate not supplied

Muscle recruitment variations during wrist flexion exercise: MR evaluation.

OBJECTIVE: Many exercise protocols used in physiological studies assume homogeneous and diffuse muscle recruitment. To test this assumption during a "standard" wrist flexion protocol, variations in muscle recruitment were assessed using MRI in eight healthy subjects. MATERIALS AND METHODS: Variations were assessed by comparing the right to the left forearms and the effect of slight (15 degrees) pronation or supination at the wrist. RESULTS: Postexercise imaging showed focal regions of increased signal intensity (SI), indicating relatively strong recruitment, most often in entire muscles, although occasionally only in subvolumes of muscles. In 15 of 26 studies, flexor carpi radialis (FCR) showed more SI than flexor carpi ulnaris, while in 11 studies SI in these muscles increased equivalently. Relatively greater FCR recruitment was seen during pronation and/or use of the nondominant side. Palmaris longus, a wrist flexor, did not appear recruited in 4 of 11 forearms in which it was present. A portion of the superficial finger flexor became hyperintense in 89% of studies, while recruitment of the deep finger flexor was seen only in 43%. CONCLUSION: Inter- and intraindividual variations in forearm muscle recruitment should be anticipated in physiological studies of standard wrist flexion exercise protocols.

Female↗
PubMedDate not supplied

The MR appearance of volume overload in the lower extremities.

PURPOSE: Our goal was to describe the MR findings of volume overload (VO) in the lower extremities. METHOD: Fifteen individuals were studied, including eight healthy controls and seven patients with VO (four cardiac, three renal). MR evaluation included various SE techniques. Edema detection, localization, and symmetry were assessed subjectively. Relaxation time estimates were also made of the subcutaneous tissue, marrow, and three muscles. RESULTS: Subcutaneous tissue was markedly edematous in seven of seven patients and asymmetric in four of seven, whereas marrow was normal in all patients. Muscle edema was mild and asymmetric in six and two of seven patients, respectively. Perifascial fluid collections were identified in six of seven patients. CONCLUSION: Subcutaneous tissue edema is the dominant feature of VO in the lower extremities. Perifascial fluid is common but does not necessarily distribute symmetrically. Muscle edema is relatively mild. These findings should aid in identifying VO as the potential cause of swelling in patients with swollen legs.

Adult↗