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Biomedical subjects

V S Lee

Publications and source records attributed to V S Lee.

At least 37 records · Page 2Linked to original sources
PubMed1999

Atheromas of the thoracic aorta: A comparison of transesophageal echocardiography and breath-hold gadolinium-enhanced 3-dimensional magnetic resonance angiography.

Transesophageal echocardiography (TEE) has been the procedure of choice for identifying thoracic aortic atheromas. All patients over a 2-year period who underwent both TEE and magnetic resonance angiography of the thoracic aorta within 1 month were identified. The largest plaque in 3 aortic segments (ascending, arch, and descending) was measured. Thirty patients (16 men; 66.8 +/- 12.9 years) were studied. The mean size of the atheromas in the arch was larger as measured by TEE compared with magnetic resonance angiography (3.4 vs 1.4 mm, P =.01). However, the mean atheroma size was similar in the ascending aorta (1.9 vs 1.3 mm, P =.5) and descending aorta (3.9 vs 3.5 mm, P =.66). Of 24 aortic segments with plaques measuring >/=5 mm (with high embolic risk), 22 (92%) were seen on TEE and only 13 (54%) on magnetic resonance angiography (P =. 003). In conclusion, although both techniques are complementary, TEE does identify more high-risk plaques.

Aged↗
PubMed1999

Single-dose breath-hold gadolinium-enhanced three-dimensional MR angiography of the renal arteries.

PURPOSE: To evaluate the quality of single-dose breath-hold three-dimensional (3D) magnetic resonance (MR) angiography of the renal arteries optimized with a 1-mL test bolus timing examination. MATERIALS AND METHODS: Three-dimensional spoiled gradient-echo imaging (3.8-4.2/1.3-1.7 [repetition time msec/echo time msec], 25 degrees-40 degrees flip angle) was performed in 60 patients after administration of gadopentetate dimeglumine (average dose, 0.11 mmol/kg). Synchronization of contrast material administration with data acquisition was achieved with a 1-mL test dose of contrast material to estimate patient circulation parameters. Image quality was assessed by using contrast-to-noise (CNR), relative vascular enhancement, and venous-to-arterial enhancement ratios and subjective scoring of arterial and venous enhancement. The effect of the contrast material injection rate and the influence of breath holding during the timing examination also were examined. RESULTS: Overall, of 60 studies, 58 were diagnostic and 56 demonstrated excellent arterial enhancement. Venous enhancement was seen in eight studies. The average aortic relative vascular enhancement (+/- SD) was 14.6 +/- 5.9, with an aorta-to-inferior vena cava (IVC) CNR of 69.7 +/- 43.9. The IVC-to-aorta venous-to-arterial enhancement ratio averaged 0.08 +/- 0.16. There was no significant difference in image quality based on injection rates or the performance of breath holding during the timing examination (P > .1). CONCLUSION: Breath-hold gadolinium-enhanced renal MR angiography free of venous enhancement can be performed consistently and reliably with 20 mL of contrast material when studies are synchronized to patient circulation time by using a timing examination.

Contrast Media↗
PubMed1999

Assessment of stenosis: implications of variability of Doppler measurements in normal-appearing carotid arteries.

PURPOSE: To examine the variability of Doppler measurements along the extra-cranial courses of the nondiseased common carotid artery (CCA) and internal carotid artery (ICA) and determine the effect of this variability on assessment of carotid arterial stenosis. MATERIALS AND METHODS: During the study period, 580 patients were referred for carotid arterial ultrasonography (US), including Doppler measurements of flow velocities in the proximal, middle, and distal portions of the CCA, in the bulb, and in the proximal and distal portions of the ICA. Eighty-five patients (average age, 59 years) with normal ICAs and CCAs formed the cohort for this study. RESULTS: The range of peak systolic velocity (PSV) measurement (maximum minus minimum) averaged 20 cm/sec +/- 13 in the CCA and 15 cm/sec +/- 13 in the ICA. ICA/CCA velocity ratios varied, depending on the CCA measurement location. In five arteries, PSV ratios exceeded a threshold of 1.8 (suggesting > or = 60% stenosis); in 23 arteries, end diastolic velocity ratios exceeded a threshold of 2.4 (also suggesting > or = 60% stenosis). Right-to-left CCA PSV ratios were abnormal in up to 26 patients (suggesting > 50% ICA stenosis), depending on where CCA measurements were obtained. When the CCA ratios were obtained at the same level, 16 were in the abnormal range. CONCLUSION: Variability of Doppler measurements in the CCA and ICA in patients without visible disease is substantial and could lead to inaccuracies in carotid arterial stenosis assessment.

Blood Flow Velocity↗
PubMed1999

Abdominal MR imaging with a volumetric interpolated breath-hold examination.

PURPOSE: To compare a T1-weighted, three-dimensional (3D), gradient-echo (GRE) sequence for magnetic resonance (MR) imaging of the body (volumetric interpolated breath-hold examination, or VIBE) with a two-dimensional (2D) GRE breath-hold equivalent. MATERIALS AND METHODS: Twenty consecutive patients underwent 1.5-T MR imaging. The examinations included pre- and postcontrast (20 mL gadopentetate dimeglumine) fat-saturated 2D GRE breath-hold imaging and fat-saturated volumetric interpolated breath-hold imaging before, during (arterial phase), and after injection, with thin (2-mm source images) and thick (8-mm reconstruction images) sections. The three images were compared qualitatively and quantitatively (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]). RESULTS: Qualitatively, the 2-mm source images had poorer pancreatic edge definition on precontrast images compared with the other two data sets (P < .05). On gadolinium-enhanced images, scores for clarity of pancreatic edge, number of vessels visualized, and arterial ghosting were significantly lower for the postcontrast 2D GRE images. Quantitatively, SNR measurements in the liver, aorta, and renal cortex on pre- and postcontrast images were significantly higher for the 8-mm reconstruction images than for the 2D GRE or 2-mm source images (P < .05). Aorta-to-fat CNR was significantly higher on the 8-mm reconstruction images. CONCLUSION: Fat-saturated volumetric interpolated breath-hold images have quality comparable to that of conventional fat-saturated 2D GRE images.

Abdomen↗
PubMed1999

Thoracic aorta: rapid black-blood MR imaging with half-Fourier rapid acquisition with relaxation enhancement with or without electrocardiographic triggering.

PURPOSE: To evaluate and compare findings for thoracic aortic disease with three black-blood magnetic resonance (MR) pulse sequences: half-Fourier rapid acquisition with relaxation enhancement (RARE), with and without electrocardiographic (ECG) triggering, and ECG-triggered turbo spin echo (SE). MATERIALS AND METHODS: Axial black-blood MR images of the chest acquired at 1.5 T with a phased-array coil were obtained in 38 consecutive patients referred for evaluation of thoracic aortic disease. ECG-triggered and nontriggered half-Fourier RARE images were compared with T1-weighted ECG-triggered turbo SE images. Two readers independently scored images for each of the following parameters: ghosting artifacts; clarity of the mediastinum, cardiac chambers, and aortic wall; conspicuity of abnormality; intraluminal signal void uniformity; and overall image quality. RESULTS: Both half-Fourier RARE sequences outperformed the turbo SE sequence for all measured parameters. Scores for the ECG-triggered half-Fourier RARE sequence were significantly (P < .05) higher than those for the nontriggered version for clarity of the mediastinum and aortic wall, conspicuity of any abnormality other than aortic dissection, and overall image quality. Mean acquisition times for the ECG-triggered (48 seconds) and nontriggered (30 seconds) sequences were significantly shorter than that for the turbo SE sequence (2 minutes 20 seconds). CONCLUSION: Rapid black-blood half-Fourier RARE sequences, with or without ECG triggering, can replace ECG-triggered turbo SE sequences for evaluation of thoracic aortic disease.

Adult↗
PubMed1999

Ventilation-perfusion lung scintigraphy as a guide for pulmonary angiography in the localization of pulmonary emboli.

PURPOSE: To assess the appropriateness of ventilation-perfusion (V-P) scintigraphic abnormalities as a guide to pulmonary angiography for the diagnosis of pulmonary embolism (PE). MATERIALS AND METHODS: V-P scintigrams and pulmonary angiograms of 104 patients with angiographically proved PE were reviewed by two nuclear medicine physicians and two interventional radiologists. For V-P scintigrams, the lung with the larger amount of perfusion abnormality was determined followed by identification of specific lobes. Pulmonary angiograms were similarly evaluated for lateralization and lobar distribution of PE. Conclusions were initially reached independently and subsequently by consensus. RESULTS: Interobserver agreement for lateralization was 88% (kappa = 0.75) for V-P scintigraphy and 98% (kappa = 0.96) for pulmonary angiography. In 72 patients, V-P scintigrams predicted unilateral embolus; 64 patients underwent pulmonary angiography of the suspected side. Eight patients underwent contralateral angiography only. Of the 64 patients, 61 (95%) had PE on the predicted side at angiography. V-P scintigrams predicted lobar distribution in 55 patients. Of these, PE was found in the predicted lobe in 42 (76%). CONCLUSION: Localization of perfusion abnormalities at V-P scintigraphy provides useful information for the interventional radiologist and serves as an accurate guide for determining the initial approach for pulmonary angiography.

Adult↗
PubMed1999

Three-dimensional gadolinium-enhanced MR venographic evaluation of patency of central veins in the thorax: initial experience.

PURPOSE: To assess the usefulness of three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) venography for evaluation of thoracic central veins. MATERIALS AND METHODS: A retrospective study included 15 patients who underwent 3D gadolinium-enhanced subtraction MR venography with a spoiled gradient-echo sequence before and at multiple times after intravenous administration of 30-40 mL of contrast material. Maximum intensity projection and multiplanar reconstruction images were used to categorize central veins as patent, occluded, or narrowed. Results were compared with findings (in 12 patients) at conventional venography (n = 3), attempted central venous catheter placement (n = 3), or surgery (n = 6). Medical records were retrospectively reviewed to determine if patient care was affected by MR venographic findings. RESULTS: By using MR venograms, an appropriate vessel could be identified for successful placement of a catheter, indwelling venous access device, or arteriovenous hemodialysis graft in all nine patients in whom placement was attempted. MR venography also was predictive of unsuccessful hemodialysis catheter placement in one patient. Conventional venographic findings confirmed MR venographic findings in three patients; in a fourth patient, conventional venography was unsuccessful due to inadequate access. MR venographic findings influenced treatment in 14 patients. CONCLUSION: On the basis of these initial results, 3D gadolinium-enhanced MR venography may facilitate comprehensive evaluation of abnormalities of the central veins in the thorax, particularly with regard to selection of venous access sites.

Adult↗
PubMed1999

Thoracic aorta: comparison of single-dose breath-hold and double-dose non-breath-hold gadolinium-enhanced three-dimensional MR angiography.

OBJECTIVE: The purpose of this study was to compare single-dose (0.1 mmol/kg) breath-hold gadolinium-enhanced three-dimensional (3D) MR angiography and double-dose (0.2 mmol/kg) non-breath-hold 3D MR angiography for evaluation of thoracic aortic disease. MATERIALS AND METHODS: Twenty-five patients referred for MR evaluation of the thoracic aorta underwent non-breath-hold gadolinium-enhanced 3D MR angiography on a 1.5-T scanner with standard gradients (TR/TE, 21/6; flip angle, 30 degrees) during slow infusion of a double dose of gadopentetate dimeglumine using a body coil. Subsequently, the same patients underwent breath-hold MR imaging with high-performance gradients (TR/TE, 5/2; flip angle, 30 degrees-50 degrees), a timing examination, and power injection of a single dose of gadolinium. For both studies, quantitative signal-to-noise measurements were obtained for the ascending thoracic, descending thoracic, and abdominal aorta. Three observers retrospectively evaluated each examination for degree of enhancement of the aorta, pulmonary arteries, and systemic veins; motion artifacts; and overall image quality. RESULTS: Single-dose breath-hold gadolinium-enhanced 3D MR angiography showed greater signal-to-noise ratio, fewer motion artifacts, and better overall image quality (p < .05) than the non-breath-hold double-dose technique. The single-dose technique also showed significantly better qualitative enhancement of the aortic root and ascending aorta (p < .05) and less enhancement of the pulmonary arteries, renal veins, and left internal jugular vein (p < .05). CONCLUSION: Optimized single-dose breath-hold gadolinium-enhanced 3D MR angiography is superior to double-dose non-breath-hold 3D MR angiography for evaluation of thoracic aortic disease.

Adolescent↗
PubMed1998

Automatic segmentation of magnetic resonance images of the trans-femoral residual limb.

An automatic algorithm for the extraction of the skin and bone boundaries from axial magnetic resonance images of the residual limb of trans-femoral amputees is presented. The method makes use of K-means clustering and mathematical morphology. Statistical analysis of the results indicates that the computer-generated boundaries compare favourably to those drawn by human observers. The boundaries may be used in biomechanical modelling of the interaction between the residual limb and the prosthetic socket. The limb/socket interface determines the quality of prosthetic fit, therefore knowledge of this interface is important for the improvement of socket design in order to achieve patient comfort and mobility.

Adipose Tissue↗
PubMed1998

Mortality and cancer incidence in Misasa, Japan, a spa area with elevated radon levels.

A historical cohort study was conducted in Misasa town, Tottori prefecture, Japan, where radon spas have been operating for a long time. Misasa town was divided into an elevated radon level area and a control area, with mean indoor radon levels of about 60 and 20 Bq/m3, respectively. In total, 3,083 subjects in the elevated radon level area and 1,248 in the control area, all aged 40 or older on January 1, 1976, were followed up until December 31, 1993, for a mean period of 14 years. The mortality rates from all causes exhibited no difference between the elevated radon level area and the control area for both sexes. No difference was observed in the incidence of all-site cancers (age, period-adjusted rate ratios by Poisson regression, RR = 1.06, 95% confidence interval (CI) 0.79-1.42 for males, RR = 0.90, 95% CI 0.65-1.24 for females), while stomach cancer incidence seemed to decrease for both sexes (RR = 0.70, 95% CI 0.44-1.11 for male, RR = 0.58, 95% CI 0.34-1.00 for female) and lung cancer incidence for males only seemed to increase (RR = 1.65, 95% CI 0.83-3.30 for male, RR = 1.07, 95% CI 0.28-4.14 for female) in the elevated radon level area. Caution is needed in the interpretation of these findings, however, since the individual exposure level was not measured and major confounding factors, such as smoking and diet, could not be controlled in this study.

Adult↗
PubMed1997

Primary muscle lymphoma: clinical and imaging findings.

PURPOSE: To assess the clinical and imaging findings in primary muscle lymphoma. MATERIALS AND METHODS: Seven patients with biopsy-proved primary muscle lymphoma without evidence of systemic disease underwent imaging with plain radiography or computed tomography (CT) and magnetic resonance (MR) imaging. Four underwent bone scintigraphy, and two underwent gallium scintigraphy and fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) before and after therapy. RESULTS: Plain radiographs at initial examination (n = 5) showed no bone abnormalities. Soft-tissue masses and bone marrow involvement showed isoattenuation at CT (n = 3), but at MR imaging (n = 7), all masses demonstrated increased signal intensity on T2-weighted images that involved multiple muscle compartments and typically spanned a long segment of the extremity. Adjacent bone disease was less extensive than muscle disease, and, in most cases, subcutaneous stranding or extension was observed adjacent to the masses. Good size correlation was observed between findings at MR imaging, gallium scintigraphy, and FDG PET. Two patients developed recurrent multifocal muscle lymphoma several years after initial examination. CONCLUSION: The presence of an extensive soft-tissue mass with infiltration of adjacent subcutaneous fat and minimal or no extension into the bone marrow cavity at MR imaging and normal plain radiographic findings may suggest primary muscle lymphoma.

Adolescent↗
PubMed1997

Stump-socket interface pressure as an aid to socket design in prostheses for trans-femoral amputees--a preliminary study.

A system for measuring the stump-socket interface pressure was designed and built using a strain gauged type load cell. The system was utilized to study the pressure distribution in the quadrilateral and ischial containment type sockets. Two volunteer trans-femoral amputees fitted with both types of socket participated in the experiments. Pressures were measured while the subjects were standing and during walking. The maximum pressure recorded for standing was 34 kPa and for walking 95 kPa. Comparison made between the two sockets indicated that higher pressures were recorded at the proximal brim of the quadrilateral socket whereas the ischial containment socket produces a more evenly distributed pressure profile. The pressure distribution on the medial and lateral walls of both types of socket were similar but in the anterior and posterior walls, significant differences were noted. The results obtained from this study were compared with those found in published literature and the biomechanics of the two types of socket is discussed.

Amputation Stumps↗