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Biomedical subjects

M F Levin

Publications and source records attributed to M F Levin.

At least 55 records · Page 3Linked to original sources
PubMed1994

Imaging after arthroplasty.

Arthroplasty is now an important and frequently performed orthopedic procedure. This article focuses on the imaging of abnormalities frequently encountered in patients who have undergone arthroplasty. The emphasis is on plain film analysis, although arthrography, computed tomography and nuclear medicine are also discussed. Among the problems illustrated are loosening of the prosthesis, component fatigue or failure, and infection. The authors recommend techniques to optimize imaging. Although most of the entities illustrated involve hip arthroplasty, the principles are valid for arthroplasty at other sites.

Arthrography↗
PubMed1993

Are H and stretch reflexes in hemiparesis reproducible and correlated with spasticity?

The measurement of spasticity has always presented a problem to clinicians and researchers alike. As yet, there is no literature addressing the reproducibility of the existing barrage of clinical evaluations of spasticity and reflex measurement. Also not clear is whether or not a systematic relationship might exist between these multiple indices of spasticity. After delineating the differences in spasticity scores and reflex functions between spastic and normal states, the aims of this study were to examine the reliability of these measurements in hemiparetic subjects, and the correlation between altered reflex functions and clinically measured spasticity. An aggregate of lower limb reflexes was compared between ten spastic hemiparetic and seven age-matched normal subjects. Lower limb reflexes examined were: (1) the ratio of maximal H reflex to M response (H/M ratio), (2) the inhibition of the H reflex during vibration (Hvib/Hctl ratio), and (3) soleus stretch reflexes (SR/M ratio). H and stretch reflex latencies were shorter (P < 0.05), and reflex amplitudes were significantly greater (H/M ratios, P < 0.05; SR/M areas, P < 0.005) in spastic subjects. While H/M ratios, Hvib/Hctl ratios, SR/M areas and SR onset angles were highly reproducible, only some physiological measurements showed consistent but non-significant relationships with clinical spasticity. The decreased reflex latencies and increased reflex responses in the hemiparetic subjects suggested that spasticity may be related to reduced reflex thresholds. The physiological measurements and clinically assessed tone were both valid and reproducible, indicating that they can be used to evaluate the long-term effects of therapeutic intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Stretch reflex latencies in spastic hemiparetic subjects are prolonged after transcutaneous electrical nerve stimulation.

Low-intensity repetitive electrical stimulation such as dorsal column and transcutaneous electrical nerve stimulation (TENS) reportedly decreases spasticity and improves voluntary motor control. However, the mechanisms mediating these effects are unclear. Recent findings suggest that spasticity may be characterized more appropriately by a decrease in the stretch reflex threshold than by an increase in gain. Our objectives were: (1) to examine possible changes in stretch reflex excitability following 45 min of TENS, (2) to map out the time course of possible post-stimulation effects via both latency and magnitude (amplitude or area) measurements, and (3) to determine the role of segmental versus non-segmental mechanisms involved in mediating these changes. The effects of 45 min of segmentally and heterosegmentally applied TENS on lower limb reflexes in ten spastic hemiparetic subjects were contrasted with those resulting from placebo stimulation. We found that both segmentally and heterosegmentally applied TENS caused an immediate increase in soleus H reflex latencies that was evident for up to 60 minutes post-stimulation in over 75% of the subjects. Similar increases for up to 60 and 40 minutes post-stimulation was noted for the stretch reflex latencies in 50% and 67% of the subjects respectively for segmental and heterosegmental stimulation. These results suggested that manipulation of segmental and heterosegmental afferents for 45 min may lead to a decrease of the otherwise augmented stretch reflex excitability accompanying hemiparetic spasticity.

Adult↗
PubMed1993

Diagnosis of osteoid osteoma using STIR magnetic resonance imaging.

Two patients with osteoid osteomas were evaluated with magnetic resonance imaging at 1.5 T using both conventional spin-echo (SE) and short TI inversion-recovery (STIR) sequences. On plain films the classic findings of a radiolucent nidus with a dense surrounding reactive zone of sclerosis were absent. The diagnosis was suspected on observing the presence of marked marrow oedema in the involved bone. Conventional SE images were unimpressive in detecting the bone marrow changes. Increased signal intensity indicating bone marrow oedema was striking on the STIR images and facilitated diagnosis. In cases of suspected osteoid osteoma which do not demonstrate the classic radiologic features, adding the STIR sequence to conventional SE magnetic resonance sequences to enhance detection of bone marrow change is recommended.

Adult↗
PubMed1993

Producing picture-perfect posters.

Scientific posters form an integral part of many radiology meetings. They provide the opportunity for interested parties to read the material at an individualized pace, to study the images in detail, and to return to the exhibit numerous times. Although the content of the poster is undoubtedly its most important component, the visual presentation of the material can enhance or detract from the clarity of the message. With the wide availability of sophisticated computer programs for desktop publishing (DTP), one can now create the poster on a computer monitor with full control of the form as well as the content. This process will result in a professional-appearing poster, yet still allow the author the opportunity to make innumerable revisions, as the poster is visualized in detail on the computer monitor before printing. Furthermore, this process is less expensive than the traditional method of typesetting individual sections separately and mounting them on cardboard for display. The purpose of this article is to present our approach to poster production using commercially available DTP computer programs.

Computer Graphics↗
PubMed1993

Three-dimensional sonographic reconstruction: techniques and diagnostic applications.

In this review, we summarize the techniques of obtaining and reconstructing three-dimensional (3D) sonograms in a number of anatomic areas, catalog the clinical efforts at 3D sonography so far, and introduce more recent work in this area that takes advantage of the unique features of sonography. Although it is an active area of 3D imaging research, cardiac 3D imaging is not discussed because it has unique requirements stemming from the heart's anatomic inaccessibility and motion. Image analysis and display also are not covered, as no clear consensus has been reached about the usefulness of the large number of available methods.

Female↗
PubMed1993

Dynamic abdominal computed tomography: "top-down" compared with "bottom-up" imaging.

Dynamic contrast-enhanced computed tomography (CT) of the liver is usually performed from the top down, and there is usually less opacification of the top slices than the more inferior slices. The authors reasoned that reversing the direction of scanning would allow more time for the parenchyma at the top of the liver to become enhanced and would result in better opacification of the parenchyma and the hepatic veins. To test this hypothesis they assigned 32 patients to either a "top-down" or a "bottom-up" group; each patient then underwent unenhanced and contrast-enhanced CT. The method of intravenous administration of contrast agent was identical in the two groups and consisted of rapid injection of 135 mL of iohexol by a power injector; scanning was initiated 30 seconds after the injection was started. Attenuation measurements were obtained at specified areas in the liver and in the hepatic and portal veins. The degree of enhancement was calculated at each site and was compared between groups. The upper portion of the liver showed significantly greater enhancement in the bottom-up sequence than in the top-down sequence (123% and 22% respectively; p < 0.01); the entire liver showed excellent enhancement in the bottom-up sequence. In addition, the hepatic veins showed significantly greater conspicuity in the bottom-up sequence (p < 0.01). The authors conclude that the dynamic bottom-up method yields excellent hepatic enhancement and vascular opacification and is therefore superior to the standard top-down method.

Adult↗
PubMed1993

Conventional and acupuncture-like transcutaneous electrical nerve stimulation excite similar afferent fibers.

The purpose of our study was to determine whether similar or different peripheral afferent fiber(s) is(are) activated by "conventional" transcutaneous electrical nerve stimulation (TENS) applied at low intensity-high frequency, as opposed to "acupuncture-like" TENS administered at high intensity-low frequency. The electrical stimulation was delivered to the median nerve at the wrist of 17 healthy subjects. For conventional TENS, single pulses were applied at an intensity of 3 X T (sensory threshold). Two kinds of acupuncture-like TENS were studied: single pulses at 0.1Hz, and trains of 100Hz pulses at 4Hz, both delivered at an intensity greater than 3 X T. Thirty compound action potentials per type of stimulation were recorded over the median nerve in the cubital fossa and averaged. The results showed that the mean conduction velocities of the afferent fibers excited by conventional TENS, single pulse, and short-train acupuncture-like TENS ranged from 50.3 to 65.4, 50.0 to 63.5, and 41.3 to 54.8m/s, respectively. Thus, conventional and acupuncture-like TENS activated similar fiber types, predominantly in the A alpha beta range. Our findings suggested that the effects of these two types of TENS may be mediated by the activation of similar peripheral afferent fibers.

Acupuncture Therapy↗
PubMed1993

Leaking Baker's cyst detected by magnetic resonance imaging.

Popliteal or Baker's cysts, often found incidentally during examination of the knee, are common. The authors report the magnetic resonance imaging (MRI) manifestations of a leaking Baker's cyst that initially presented as thrombophlebitis in a patient who had undergone reconstruction of the anterior cruciate ligament 4 months before; no cyst was present at the time of the surgery. Marked inflammatory changes apparent in the surrounding muscle and subcutaneous tissues were best appreciated in T2-weighted and fat-suppressed inversion recovery images. Although the results of ultrasonography suggested the diagnosis, they were not conclusive; MRI was a useful noninvasive adjunct in making the definitive diagnosis.

Adult↗
PubMed1993

Intravenous administration of gadolinium in the evaluation of rheumatoid arthritis of the shoulder.

The authors sought to determine the utility of intravenously administered gadolinium chelates in magnetic resonance imaging (MRI) of patients with rheumatoid arthritis of the shoulder. One shoulder was examined for each of 12 patients--6 men and 6 women, ranging in age from 48 to 71 (average 63) years--with well-established disease. The patients had had the disease for 1 to 25 (average 13) years. Static MRI was performed before and after infusion of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) (0.1 mmol/kg body weight); T1-weighted or proton-density images (repetition time [TR] 600 to 1000 ms, echo time [TE] 15 to 30 ms) were obtained. Images obtained after enhancement were particularly useful in the differentiation of pannus from fluid and also allowed improved delineation of tears of the supraspinatus tendon. In addition, contrast-enhanced dynamic gradient-echo spoiled GRASS sequences (TR 50 ms, TE 11 ms, flip angle 70 degrees) were obtained for all patients; for these sequences the same slice was imaged repeatedly at 20-second intervals. The rate of increase of signal intensity in abnormal synovium varied from 0.64 to 5.83 (average 2.30, standard deviation [SD] 1.67) units/second; the enhancement factor ranged from 1.55 to 4.64 (average 2.63, SD 0.98). The authors conclude that for imaging the shoulder enhancement with Gd-DTPA allows improved distinction between synovial thickening and joint effusion and may improve assessment of the rotator cuff. The wide range in the rate of signal increase and total enhancement during dynamic imaging probably reflected heterogeneity in the study population.

Acromioclavicular Joint↗
PubMed1993

Sonolucent peripancreatic masses: differential diagnosis and related imaging.

The most common cause of a sonolucent mass in the epigastrium is a pancreatic pseudocyst; however, several other conditions can simulate a pseudocyst on ultrasonography (US) scans. This pictorial essay illustrates the spectrum of conditions that may present in this fashion and demonstrates the use of other imaging modalities, such as colour-flow and pulsed Doppler US, computed tomography, magnetic resonance imaging and angiography, in their evaluation.

Abscess↗
PubMed1992

Reciprocal and coactivation commands for fast wrist movements.

According to the equilibrium-point hypothesis, movements are produced by means of displacement of the invariant torque/angle characteristic (IC) of the joint and change in its slope. Displacement is produced via the central reciprocal (R) command while the coactivation (C) command specifies the slope of the IC. Neurophysiologically, the R command is associated with reciprocal changes in the membrane potentials of agonist and antagonist motoneurons while the C command is associated with their simultaneous depolarisation. These commands were investigated in single joint wrist movements by perturbation methods. Subjects normally made free flexion movements to a target at 30 degrees but on random trials they were either opposed by a spring-like load or assisted by a load. The former was generated using negative linear position feedback; the latter using positive position feedback to a torque motor. Subjects were instructed not to correct errors arising from perturbations. Both peak velocity and EMG patterns were strongly affected by load conditions. Subjects undershot or overshot the target when opposing or assisting loads were presented, respectively. However, after removing the load (700 ms later), the target position was regained indicating that the IC was stable despite the perturbation. In two other experiments, subjects initially trained to reach the target with opposing or assisting loads, while on random trials, the load was not presented. Depending on training conditions, the subject shifted the IC by different amounts. The slope of the IC varied independently of the magnitude of its positional shift. We conclude that R and C commands can be specified independently.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Relief of hemiparetic spasticity by TENS is associated with improvement in reflex and voluntary motor functions.

Our previous studies showed that a single 45 min application of transcutaneous electrical nerve stimulation (TENS) prolonged soleus H and stretch reflex latencies in hemiparetic subjects. In addition, 9 daily 30 min TENS applications enhanced vibratory inhibition of the H reflex and tended to decrease hyperactive stretch reflexes. These findings suggested that longer-term TENS may be effective in reducing hemiparetic spasticity. Our present objectives were 2-fold: to determine whether longer-term repetitive TENS stimulation would lead to a reduction in clinical spasticity in hemiparetic subjects, and whether such a reduction could be associated with a decrease in stretch reflex excitability and an improvement in voluntary motor function. We compared the effects of 15 daily 60 min TENS treatments over a 3 week period, with those of placebo stimulation applied to the common peroneal nerve of the affected leg in similar groups of spastic hemiparetic subjects. Our test battery consisted of 5 measurements which assessed (1) clinical spasticity scores, (2) maximal H reflex to M response ratios, (3) vibratory inhibition of H reflex, (4) stretch reflexes, and (5) maximal voluntary isometric plantarflexion and dorsiflexion, in standing. In contrast to placebo stimulation which produced no significant effects, repeated applications of TENS over time decreased clinical spasticity (P less than 0.05), and increased vibratory inhibition of the soleus H reflex (P = 0.02) after 2 weeks. These changes occurred with a substantial improvement in voluntary dorsiflexing force up to 820%, but not plantarflexing force. They were followed by a reduction in the magnitude of stretch reflexes (P = 0.05) in the spastic ankle plantarflexor, concomitant with a decrease in the EMG co-contraction ratios after a further week of stimulation. Our results thus indicated that repeated applications of TENS can reduce clinical spasticity and improve control of reflex and motor functions in hemiparetic subjects. Furthermore, the underlying mechanisms may be due partly to an enhancement in presynaptic inhibition of the spastic plantarflexor, and partly to a possible "disinhibition" of descending voluntary commands to the paretic dorsiflexor motoneurons.

Aged↗
PubMed1992

CT findings in patients with small-bowel transplants.

Orthotopic small-bowel transplantation procedures are being performed increasingly often worldwide. CT plays an important role in both the preoperative assessment and the postoperative care of these patients. This pictorial essay serves to acquaint radiologists with the CT findings related to small-bowel transplantation.

Abscess↗