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Biomedical subjects

K C Li

Publications and source records attributed to K C Li.

At least 55 records · Page 3Linked to original sources
PubMed1996

A study of factors affecting indoor radon properties.

The factors affecting indoor radon properties in Hong Kong have been studied, including the radon concentration, the total potential alpha energy concentration of radon progeny, the equilibrium factor, and the fraction of unattached radon progeny. These factors fall into three categories, namely, (1) the building characteristics, including cooling method, age of the buildings, wall coverings and floor coverings; (2) the location of sites, including nearby environments, geological materials of the area, and the elevation of the sites; and (3) the meteorological parameters, including rainfall, relative humidity, pressure, temperature, and wind speeds. For category (1), only the ventilation is found to affect the indoor radon properties. For category (2), only the nearby environments have effects. For category (3), the rainfall and temperature are found to have significant effects.

Air Pollutants, Radioactive↗
PubMed1996

Power Doppler imaging of focal lesions of the gastrointestinal tract: comparison with conventional color Doppler imaging.

To compare the usefulness of power Doppler imaging and color Doppler imaging in the vascular evaluation of gastrointestinal lesions, 21 patients with focal gastrointestinal tract lesions were examined with both power and color Doppler imaging. Two reviewers blinded to the diagnosis compared intramural vascularity detected by each of these methods. Power Doppler imaging detected flow in 16 patients with nonischemic lesions, whereas color Doppler imaging detected flow in only 11 patients. Neither modality detected flow in three patients with transmural infarction, but only power Doppler imaging detected minimal flow in the two patients with reversible ischemia. Power Doppler imaging improves visualization of intramural gastrointestinal vascularity, increasing the level of confidence in differentiating ischemic from nonischemic lesions.

Adult↗
PubMed1995

Gadolinium-DTPA-enhanced magnetic resonance imaging of musculoskeletal infectious processes.

The purpose of this study was to assess whether gadolinium-enhanced magnetic resonance imaging (MRI) provides diagnostic information beyond that given by nonenhanced imaging in the evaluation of musculoskeletal infectious processes and whether it can be used for differentiating infectious from noninfectious inflammatory lesions. Magnetic resonance images performed with and without intravenous gadolinium-DTPA in 34 cases in which musculoskeletal infection had been clinically suspected were reviewed. Infectious lesions--including osteomyelitis, pyarthrosis, abscess, and cellulitis--were confirmed in a total of 22 cases: in 15 by biopsy or drainage and in 7 by clinical course. Our results show that gadolinium-DTPA-enhanced MRI is a highly sensitive technique in diagnosing musculoskeletal infectious lesions. It is especially useful in distinguishing abscesses from surrounding cellulitis/myositis. Lack of contrast enhancement rules out infection with a high degree of certainty. However, contrast enhancement cannot be used to reliably distinguish infectious from noninfectious inflammatory conditions.

Abscess↗
PubMed1995

Magnetization transfer contrast MRI of musculoskeletal neoplasms.

Magnetic resonance imaging (MRI) examinations were performed in 15 patients with musculoskeletal neoplasms to assess the value of magnetization transfer contrast in tumor characterization. Multiplanar gradient-recalled echo sequences (TR 500-600/TE 15-20/flip angle 20-30 degrees) were performed first without and then with magnetization transfer contrast generated by a zero degree binomial pulse (MPGR and MTMPGR). Standard T1-weighted spin echo images (SE; TR 300-400/TE 12-20) and either T2-weighted SE (TR 2000-2900/TE 70-80) or T2-weighted fast spin echo (FSE; TR 4000-5000/TE 100-119 effective) images were also obtained. Signal intensities on MTMPGR scans were compared to those on MPGR scans for both tumors and normal tissues. Signal intensity ratios (SIR) and contrast-to-noise ratios (CNR) were also compared for all sequences. MTMPGR images provided better contrast between pathologic tissues and muscle than did standard MPGR images, increasing both conspicuity of lesions and definition of tumor/muscle interfaces. Benign and malignant tumors, with the exception of lipoma, underwent similar degrees of magnetization transfer and could not be distinguished by this technique.

Adipose Tissue↗
PubMed1995

Oxygen saturation of blood in the superior mesenteric vein: in vivo verification of MR imaging measurements in a canine model. Work in progress.

PURPOSE: To evaluate the accuracy of magnetic resonance (MR) imaging in estimating oxygen saturation of blood (%HbO2) in the superior mesenteric vein (SMV) of a canine model in vivo. MATERIALS AND METHODS: MR imaging was used to measure the T2 of blood in samples obtained via a catheter placed in the SMV in seven mongrel dogs. %HbO2 was measured with a reflectance oximeter. These measurements were obtained at the resting state, during superior mesenteric artery occlusion, and after reperfusion. MR imaging and oximeter measurements were then compared by using linear regression analysis. RESULTS: Refocusing intervals (tau 180) of 12 and 24 msec were used for 17 and 18 %HbO2 measurements with MR imaging, respectively. With tau 180 of 12 msec, there was an excellent correlation between MR imaging measurements and oximeter measurements (r = .969). The intercept was 5.3% and the slope was 0.959. With tau 180 of 24 msec, r = .953, the intercept was 15.4%, and the slope was 0.817. CONCLUSION: Estimates of %HbO2 in the SMV with MR imaging are accurate in the range of most clinical interest.

Animals↗
PubMed1995

Simultaneous measurement of flow in the superior mesenteric vein and artery with cine phase-contrast MR imaging: value in diagnosis of chronic mesenteric ischemia. Work in progress.

PURPOSE: To evaluate the use of measurements of blood flow in the superior mesenteric vein (SMV) and superior mesenteric artery (SMA) simultaneously acquired with phase-contrast cine magnetic resonance (MR) imaging for diagnosing chronic mesenteric ischemia. MATERIALS AND METHODS: Simultaneous measurements of flow in the SMV and SMA were obtained in six healthy volunteers and eight patients with angiographically proved SMA stenosis (six asymptomatic, two symptomatic). Flow dynamics in both vessels were correlated with the degree of arterial disease seen at angiography and with the presence or absence of ischemic symptoms. RESULTS: Postprandial SMV and SMA flow increased substantially less in patients with atherosclerosis than in volunteers. Comparison of simultaneous SMV and SMA flow measurements provided more information about collateral flow to and from the mesenteric circulation than did either the SMV or SMA flow measurement alone. CONCLUSION: Simultaneous SMV and SMA flow measurement with cine phase-contrast MR imaging may be useful in diagnosing and understanding chronic mesenteric ischemia.

Adult↗
PubMed1994

Chronic mesenteric ischemia: evaluation with phase-contrast cine MR imaging.

PURPOSE: To compare superior mesenteric artery (SMA) blood flow in healthy volunteers and patients with stenoses in the fasting state and after food intake by using phase-contrast (PC) cine magnetic resonance (MR) imaging. MATERIALS AND METHODS: Ten healthy subjects, four asymptomatic patients (three with 50% stenosis, one with 70% stenosis), and one symptomatic patient (with 80% stenosis) were studied. All subjects were studied after fasting at least 8 hours and 15, 30, and 45 minutes after ingesting a standard meal. RESULTS: In healthy volunteers, SMA blood flow at all postprandial intervals increased significantly compared with that obtained after fasting (P < or = .0005). The percentage change in SMA blood flow 30 minutes after food intake provided the best distinction between the healthy subjects, the asymptomatic patients, and the symptomatic patient. CONCLUSION: Cine PC MR imaging is an effective, noninvasive technique for measuring SMA blood flow.

Adult↗
PubMed1994

Quantitative magnetic resonance flow imaging.

Time-of-flight and phase shift methods have both been used for vascular imaging with magnetic resonance. Phase methods, and phase contrast in particular, are well suited to quantitative measurements of velocity and volume flow rate. The most robust methods for measuring flow encode through-plane velocity into phase shift and compute flow by integrating the measured velocity over the vessel lumen. The accuracy of the flow data can be degraded by the effects of acceleration and eddy currents and by partial volume effects, including the effects of finite slice thickness and resolution, pulsatile waveforms, motion, and chemical shift. The reproducibility depends on the signal-to-noise of the data and the strength of the flow encoding and can be degraded by inconsistent definition of the vessel boundary. The adjustable flow sensitivity inherent in this method is a particular asset, allowing phase contrast flow measurement to operate over a dynamic range exceeding 10(5). Recently developed rapid imaging methods are helpful in applications that would be compromised by respiratory motion. With care, excellent quantitative data can be quickly obtained in vivo, and the resulting flow information is valuable for the diagnosis and management of a variety of conditions.

Humans↗
PubMed1993

Experimental hepatic tumor necrosis. Comparison of spin-echo and pulsed magnetization transfer contrast magnetic resonance imaging.

RATIONALE AND OBJECTIVES: We compared the effectiveness of pulsed magnetization transfer contrast (MTC) magnetic resonance imaging (MRI) and spin-echo MRI in detecting tumor necrosis. METHODS: Adenocarcinoma cells were transplanted in the livers of 12 syngenic BDIX rats. To induce various degrees of tumor necrosis, the rats were randomly assigned to the following groups: 1) control; 2) localized hyperthermia; 3) intralesional cisplatin; and 4) hyperthermia plus intralesional cisplatin. At day 7 after treatment, the rats were imaged using a 1.5-T imager with 1) multiplanar gradient-recalled echo sequence (MPGR) 500/8/20 degrees with and without magnetization transfer contrast (MTC); 2) spin-echo 2500/20,80, and 3) spin-echo 300/20 pulse sequences. The rats were then sacrificed and pathologic specimens were prepared using MR images as guidance. T2 and ratios of signal intensity after saturation to signal intensity before saturation (Ms/Mo ratios) of the necrotic and granulation tissues and viable tumors were determined in 10 rats. RESULTS: Compared with standard MPGR images, MPGR images with MTC provided better contrast between the pathologic tissues and normal liver. However, T2 values were more useful than Ms/Mo ratios in distinguishing necrotic areas from viable tumor. The T2 values of coagulative necrosis and granulation tissue were significantly different from that of viable tumor. No significant difference between the Ms/Mo ratios of the different pathologic tissues and normal liver was found. CONCLUSION: Pulsed magnetization transfer contrast MRI was inferior to spin-echo MRI in distinguishing necrotic from viable tumors in rat livers using the pulse sequences described, and none of the sequences studied was thought to be reliable enough for this purpose.

Adenocarcinoma↗
PubMed1993

Dynamic breath-hold multiplanar spoiled gradient-recalled MR imaging with gadolinium enhancement for differentiating hepatic hemangiomas from malignancies at 1.5 T.

PURPOSE: To compare the enhancement patterns of focal liver lesions at dynamic breath-hold gadolinium-enhanced multiplanar spoiled gradient-recalled (SPGR) magnetic resonance (MR) imaging with T2 relaxation times in the differentiation of liver hemangiomas from malignancies. MATERIALS AND METHODS: Forty-seven patients with focal liver lesions underwent MR imaging with spin-echo and gadolinium-enhanced multiplanar SPGR techniques. T2 relaxation times and enhancement patterns were compared for accuracy in liver lesion characterization. RESULTS: Enhancement patterns allowed better characterization of liver lesions than did T2 relaxation times. Only specific patterns of contrast enhancement indicated a hemangioma. Although 18 of the 33 malignancies and 10 of the 12 hemangiomas showed progressive centripetal hyperintense enhancement, only hemangiomas filled in with hyperintense peripheral nodules. Malignancies often filled in with hyperintense thick rinds. CONCLUSION: Gadolinium-enhanced multiplanar SPGR imaging allows more accurate characterization of liver lesions than does T2 relaxation time.

Adult↗
PubMed1992

Contrast-enhanced fat saturation magnetic resonance imaging for studying the pathophysiology of osteonecrosis of the hips.

We imaged 75 hips in 40 patients using fat saturation technique before and after intravenous injection of contrast (0.1 mmol/kg gadolinium diethylene triamine penta-acetic acid, Gd-DTPA). Eighteen hips in 11 patients were determined to be osteonecrotic, either by pathologic or clinical examination. In the osteonecrotic hips, three distinct patterns of enhancement were found: (I) focal area outlined by brightly enhancing rim (7 hips); (II) diffuse enhancement in the femoral head and neck extending into the femoral shaft (3 hips); and (III) a combination of patterns I and II (8 hips). Our data support the hypothesis that early nontraumatic osteonecrosis is associated with hyperemia and/or an increase in capillary permeability rather than acute devascularization, and that diffuse marrow edema is the initial finding in early nontraumatic osteonecrosis.

Capillary Permeability↗
PubMed1992

In vivo MR evaluation of Gd-DTPA conjugated to dextran in normal rabbits.

A dextran-Gd-DTPA compound has been recently synthesized utilizing 70,800 Da molecular weight dextran. This polymeric contrast agent for magnetic resonance imaging has been found chemically to be very stable and to demonstrate in vitro improved relaxivities of 1.5 to 2.3 times that of monomeric Gd-DTPA at 100 MHz. This MR experiment examines the in vivo distribution and relaxivity of the 70,800 Da molecular weight dextran-Gd-DTPA compound in a rabbit model by measuring the change in signal-to-noise ratio of a variety of organs (renal cortex, renal medulla, liver, brain, and torcula herophile) compared to the preinjection state. Results demonstrate prolonged (beyond 60 min) enhancement of the renal cortex, renal medulla, liver and torcula, and no enhancement of brain parenchyma.

Animals↗
PubMed1992

Screening test for detection of metallic foreign objects in the orbit before magnetic resonance imaging.

RATIONALE AND OBJECTIVES: A study was designed to determine whether plain films, used as a screening modality for magnetic resonance imaging (MRI), could reliably detect intraorbital metallic foreign objects. METHODS: In the first experiment, 20 metal particles were placed in five human cadaver orbits. Routine orbital plain film series and computed tomography (CT) were obtained, randomized, and interpreted blinded by three experienced radiologists. RESULTS: The threshold size of particle detection for CT (0.07 mm3) was lower than for plain films (0.12 mm3). Placing metal particles in artificial and true vitreous demonstrated that all particles moved under a magnetic field at 1.5 T. When human globes were exposed to industrial tools (grinder, bandsaw, air hose, etc.), no metal objects penetrated the sclera. CONCLUSIONS: Plain films can be used as a low-cost, low-radiation screening procedure for high-risk patients with occupations involving metal work. CT should be used for patients with a history of eye trauma from other causes.

Costs and Cost Analysis↗
PubMed1992

The pelvis: T2-weighted fast spin-echo MR imaging.

Fast spin-echo (SE) T2-weighted magnetic resonance (MR) imaging provides images with highly T2-weighted contrast in substantially reduced imaging times. In a prospective evaluation, fast SE T2-weighted imaging of the pelvis was compared with conventional SE T2-weighted imaging in 30 consecutive patients in whom pelvic pathologic conditions were suspected. Three reviewers independently analyzed the images for (a) overall image quality, (b) pelvic organ definition, (c) conspicuity of pelvic fluid, and (d) conspicuity of pelvic pathologic conditions. Fast SE images were rated superior to conventional SE T2-weighted images in 60% (54 of 90) of the case reviews for overall image quality, in 69% (62 of 90) for pelvic organ definition, in 63% (57 of 90) for conspicuity of pelvic fluid, and in 68% (43 of 63) for conspicuity of pelvic pathologic conditions. The fast SE examinations were typically three to four times faster than conventional SE T2-weighted examinations. No pathologic findings seen on conventional SE T2-weighted images were undetected on fast SE images. Fast SE images may replace conventional SE T2-weighted images in MR imaging of the pelvis.

Abdomen↗
PubMed1991

Barium sulfate suspension as a negative oral MRI contrast agent: in vitro and human optimization studies.

In vitro proton spectroscopy with line-width measurements and MR imaging were performed on various concentrations of commercially available single contrast (SC), double contrast, oral and rectal barium sulfate suspensions, as well as potassium sulfate, barium chloride, barium hydroxide, and 97% pure barium sulfate suspensions. Approximately 500 ml of 20%, 40%, 60%, and 70% w/w suspensions of SC oral barium sulfate suspensions were administered to four normal volunteers, respectively, and MR images were obtained at both 1.5 T and 0.15 T. Subsequently, 500 ml of 60% w/w suspensions of SC oral barium sulfate suspensions were administered to five normal volunteers and imaged at 1.5 T. All of the inert suspensions produced line-width broadening but the SC oral barium sulfate suspension at 50% and 70% stayed in suspension even after hours of standing undisturbed. As much as 80% of the small bowel and the entire colon were well visualized using the combination of 60% or 70% w/w SC barium sulfate suspensions with SE 550/22 and FISP pulse sequences. The effect was less at 0.15 T and also with the SE 2000/45/90 pulse sequences. We conclude that barium sulfate suspensions are useful as oral MRI contrast agents.

Administration, Oral↗
PubMed1991

Enteric MRI contrast agents: comparative study of five potential agents in humans.

We compared the effectiveness of 1 mM Geritol, 12% corn oil emulsion, Kaolin-pectin, single contrast oral barium sulfate, and effervescent granules as enteric magnetic resonance imaging (MRI) contrast agents. Five volunteers were recruited. Each volunteer ingested for examinations, separated by at least one week, either 500 ml of each of the liquid preparations or two packets of the CO2 granules (producing 400 ml of CO2 per packet). Abdominal MR images were then obtained using a 1.5 T Magnetom imager and SE 550/22, SE 2000/45/90 and FISP 40/18/40 degrees pulse sequences. The oil emulsions were best tolerated. Barium sulfate caused the greatest amount of nausea, followed by Geritol and Kaolin-pectin. With FISP 40/18/40 degrees, 60%-80% of the small bowel was well delineated using oil emulsion, Kaolin-pectin, or barium sulfate. We conclude that oil emulsion was by far the best enteric MR contrast agent in our study. Good delineation of the small bowel and pancreas can be achieved using oil emulsion and gradient echo pulse sequences. The lack of side-effects and the excellent taste make it highly acceptable to human subjects.

Abdominal Pain↗