Biomedical subjects

K C Li

Publications and source records attributed to K C Li.

At least 37 records · Page 2Linked to original sources

PubMed1998

Detection of tumor angiogenesis in vivo by alphaVbeta3-targeted magnetic resonance imaging.

Angiogenesis, the formation of new blood vessels, is a requirement for malignant tumor growth and metastasis. In the absence of angiogenesis, local tumor expansion is suppressed at a few millimeters and cells lack routes for distant hematogenous spread. Clinical studies have demonstrated that the degree of angiogenesis is correlated with the malignant potential of several cancers, including breast cancer and malignant melanoma. Moreover, the expression of a specific angiogenesis marker, the endothelial integrin alphaVbeta3, has been shown to correlate with tumor grade. However, studies of tumor angiogenesis such as these have generally relied on invasive procedures, adequate tissue sampling and meticulous estimation of histologic microvessel density. In the present report, we describe a novel approach to detecting angiogenesis in vivo using magnetic resonance imaging (MRI) and a paramagnetic contrast agent targeted to endothelial alphaVbeta3 via the LM609 monoclonal antibody. This approach provided enhanced and detailed imaging of rabbit carcinomas by directly targeting paramagnetic agents to the angiogenic vasculature. In addition, angiogenic 'hot spots' not seen by standard MRI were detected. Our strategy for MR imaging of alphaVbeta3 thus represents a non-invasive means to assess the growth and malignant phenotype of tumors.

Animals↗

PubMed1998

Description of Songshupsylla, a new subgenus of Macrostylophora (Siphonaptera: Ceratophyllidae), with a discussion of its species groups.

The new subgenus Songshupsylla is erected to include certain species heretofore included in Macrostylophora s. lat. Ewing, 1929. The subgenus is further divided into 2 species groups according to their morphological characters and geographical distribution in the Paleartic and Oriental Regions. Brief descriptions of these species groups and the names of the Chinese taxa are given.

Animals↗

PubMed1998

Magnetic resonance angiography of mesenteric arteries. A review.

There has been continued development of MRI techniques for evaluating mesenteric vascular disease. Contrast-enhanced magnetic resonance angiography (MRA) can provide reproducible high resolution, high contrast images of the arterial and venous mesenteric vasculature and may allow detection of segmental ischemia by detection of segmental delayed mesenteric or bowel wall enhancement. Cine phase-contrast MRA can provide additional information about the rate and volume of flow within the major mesenteric arteries and veins. Real-time MRI can provide interactive visualization of the mesenteric vessels in any plane, and with suitable bowel contrast, it can be used to monitor global and segmental small bowel motility. With in vivo MR oximetry, flow independent measurements of the T2 relaxation of blood allow the oxygen saturation of the mesenteric circulation to be determined. These MR techniques can be combined for evaluating both anatomic and functional aspects of the mesenteric circulation.

Blood Flow Velocity↗

PubMed1998

Mesenteric ischemia due to hemorrhagic shock: MR imaging diagnosis and monitoring in a canine model.

PURPOSE: To test whether changes in the percentage of oxygenated hemoglobin (%HbO2) and blood flow in the superior mesenteric vein (SMV), as measured with magnetic resonance (MR) imaging in vivo, can be used to diagnose and monitor mesenteric ischemia due to hemorrhagic shock in a canine model. MATERIALS AND METHODS: Eight mongrel dogs (weight range, 20-30 kg) underwent fasting for 24 hours before the experiments. MR imaging measurements of SMV %HbO2 and volume flow rate were obtained at the resting state and after 5%, 10%, and 15% of the blood volume of the dogs had been removed sequentially, which led to a total blood volume depletion of 30%. In four dogs, resuscitation was performed with normal saline solution in a volume equal to the total volume of blood removed. RESULTS: SMV %HbO2 and SMV flow measurements at the different stages of blood removal were all significantly different (P < .05) from baseline measurements and from each other. After volume replacement with normal saline solution, SMV %HbO2 and flow were not significantly different (P > .05) from the baseline values. CONCLUSION: SMV %HbO2 and volume flow rate, as measured with MR imaging in vivo, can be used to diagnose and monitor mesenteric ischemia due to hemorrhagic shock in a canine model.

Animals↗

PubMed1998

Anterior cruciate ligament injury: fast spin-echo MR imaging with arthroscopic correlation in 217 examinations.

OBJECTIVE: Our objective was to evaluate the accuracy of MR imaging strategy that uses primarily fast spin-echo sequences for the diagnosis of anterior cruciate ligament tears. MATERIALS AND METHODS: The original clinical interpretations of MR images of 217 examinations of the knee joint were correlated with subsequent arthroscopic results. Each MR examination included a double-echo fast spin-echo sequence as the only imaging sequence in the sagittal plane. Subsequent discordant MR and arthroscopic examinations were then subjected to reanalysis by two observers who were unaware of arthroscopic results to determine if misinterpretations were observer or image dependent. Two hundred sixteen patients who underwent MR imaging for suspected internal derangement of the knee subsequently underwent arthroscopic surgery. Two patients had both knees evaluated. One patient was excluded because he was referred for evaluation for osteomyelitis, not internal derangement. This yielded a total number of 217 MR examinations for suspected internal derangement of the knee. RESULTS: For 56 arthroscopically proven tears, the sensitivity of MR imaging was 96%. The specificity was 98%, yielding an overall accuracy rate of 98%. The positive and negative predictive values were 95% and 99%, respectively. These values are within the ranges of previously reported MR imaging strategies using conventional spin-echo sequences. CONCLUSION: Fast spin-echo MR imaging of the knee can be an alternative to conventional spin-echo imaging for the detection of anterior cruciate ligament tears.

Adolescent↗

PubMed1998

Mesenteric occlusive disease.

Using contrast-enhanced MR angiography, cine phase contrast MR imaging, and flow-independent T2 measurements, MR imaging can provide both morphologic information about the degree of stenosis of the mesenteric vessels and quantitative functional information about blood flow and blood oxygen saturation in these vessels. The combination of these techniques can potentially revolutionize the diagnosis and post-treatment assessments of both acute and chronic mesenteric occlusive disease.

Acute Disease↗

PubMed1997

Real-time interactive MRI on a conventional scanner.

A real-time interactive MRI system capable of localizing coronary arteries and imaging arrhythmic hearts in real-time is described. Non-2DFT acquisition strategies such as spiral-interleaf, spiral-ring, and circular echo-planar imaging provide short scan times on a conventional scanner. Real-time gridding reconstruction at 8-20 images/s is achieved by distributing the reconstruction on general-purpose UNIX workstations. An X-windows application provides interactive control. A six-interleaf spiral sequence is used for cardiac imaging and can acquire six images/s. A sliding window reconstruction achieves display rates of 16-20 images/s. This allows cardiac images to be acquired in real-time, with minimal motion and flow artifacts, and without breath holding or cardiac gating. Abdominal images are acquired at over 2.5 images/s with spiral-ring or circular echo-planar sequences. Reconstruction rates are 8-10 images/s. Rapid localization in the abdomen is demonstrated with the spiral-ring acquisition, whereas peristaltic motion in the small bowel is well visualized using the circular echo-planar sequence.

Abdomen↗

PubMed1997

MRI of pulmonary embolism using Gd-DTPA-polyethylene glycol polymer enhanced 3D fast gradient echo technique in a canine model.

This study was to evaluate the accuracy of MR angiography (MRA) using a Gd-DTPA-polyethylene glycol polymer (Gd-DTPA-PEG) with a 3D fast gradient echo (3D fgre) technique in diagnosing pulmonary embolism in a canine model. Pulmonary emboli were created in six mongrel dogs (20-30 kg) by injecting tantalum oxide-doped autologous blood clots into the femoral veins via cutdowns. MRI was performed with a 1.5 T GE Signa imager using a 3D fgre sequence (11.9/2.3/15 degrees) following intravenous injection of 0.06 mmol Gd/kg of Gd-DTPA-PEG. The dogs were euthanized and spiral CT of the lungs were then obtained on the deceased dogs. The MRI images were reviewed independently and receiver-operating-characteristic (ROC) curves were used for statistical analysis using spiral CT results as the gold standard. The pulmonary emboli were well visualized on spiral CT. Out of 108 pulmonary segments in the six dogs, 24 contained emboli >2 mm and 27 contained emboli < or = 2 mm. With unblinded review, MRI detected 79% of emboli >2 mm and only 48% of emboli < or = 2 mm. The blinded review results were significantly worse. Gd-DTPA-PEG enhanced 3D fgre MRI is potentially able to demonstrate pulmonary embolism with fairly high degree of accuracy, but specialized training for the interpretations will be required.

Animals↗

PubMed1997

In vivo magnetic resonance evaluation of blood oxygen saturation in the superior mesenteric vein as a measure of the degree of acute flow reduction in the superior mesenteric artery: findings in a canine model.

RATIONALE AND OBJECTIVES: The authors tested the hypothesis that changes in oxygen saturation (%HbO2) in the superior mesenteric vein (SMV), as measured with in vivo magnetic resonance (MR) oximetry, correlate with the degree of acute superior mesenteric artery (SMA) flow reduction. METHODS: Ten mongrel dogs were studied. A catheter was inserted into the SMV, and a perivascular ultrasonic flow probe and an adjustable mechanical occluder were placed around the SMA. MR oximetry was carried out at the resting state and after the SMA was constricted to predetermined levels (0%-75% of initial flow). In seven dogs, SMV blood samples were obtained immediately before and after each MR measurement; %HbO2 was measured simultaneously by using an oximeter. With linear regression analysis, the SMV %HbO2 measurements obtained at MR imaging were compared with those obtained at oximetry. With a logistic model, MR imaging changes in SMV %HbO2 were compared with the degree of SMA flow reduction. RESULTS: SMV %HbO2 measurements obtained with MR imaging correlated well with those obtained with oximetry (r = .97). Changes in SMV %HbO2 measured at MR imaging also correlated well with the degree of SMA flow reduction, as determined with a logistic model (P = .01). CONCLUSION: Noninvasive in vivo MR measurements of SMV %HbO2 can be used to determine the degree of acute SMA flow reduction with a high degree of accuracy in a canine model.

Animals↗

PubMed1997

Magnetic resonance angiography of the visceral arteries: techniques and current applications.

In recent years, the techniques of contrast-enhanced magnetic resonance angiography, cine phase-contrast magnetic resonance imaging, and in-vivo magnetic resonance oximetry have been used in the diagnosis of visceral vascular diseases. The combination of these techniques can provide both anatomical and physiological information concerning the visceral circulation, and has the potential to revolutionize the work-up in patients with acute and chronic mesenteric ischemia.

Animals↗

PubMed1997

Meniscal tears of the knee: accuracy of detection with fast spin-echo MR imaging and arthroscopic correlation in 293 patients.

PURPOSE: To evaluate the accuracy of a magnetic resonance (MR) imaging strategy that uses primarily fast spin-echo (SE) sequences for the diagnosis of meniscal tears. MATERIALS AND METHODS: The original clinical interpretations of MR images in 293 patients who underwent imaging for suspected internal derangement of a knee joint were correlated with results from subsequent arthroscopy. MR examination included a double-echo fast SE sequence as the only imaging in the sagittal plane. RESULTS: The sensitivity and specificity for 143 confirmed tears of the medial meniscus were 89% and 84%, respectively, while the values for 96 confirmed tears of the lateral meniscus were 72% and 93%. These values are within the ranges of values recently reported for imaging strategies relying predominantly on conventional SE sequences. CONCLUSION: Fast SE imaging of the knee can be an alternative to conventional SE imaging for the detection of meniscal tears.

Adolescent↗

PubMed1997

Chronic mesenteric ischemia: use of in vivo MR imaging measurements of blood oxygen saturation in the superior mesenteric vein for diagnosis.

PURPOSE: To determine if dogs and humans with chronic mesenteric ischemia demonstrate a decrease in the percentage of oxygenated hemoglobin (%HbO2) in the superior mesenteric vein (SMV) after a meal. MATERIALS AND METHODS: In 10 dogs, ameroid rings were surgically implanted around the superior mesenteric arteries to create gradual stenosis. Pre- and postoperative angiograms and pre- and postprandial magnetic resonance (MR) oximetry measurements of the SMV %HbO2, with flow-independent T2 measurements of venous blood, were obtained at different times. In 10 patients with atherosclerotic disease and six patients with symptomatic chronic mesenteric ischemia, the same measurements were obtained after at least 6 hours of fasting and at 15, 35, and 45 minutes after ingestion of a liquid nutritional supplement. RESULTS: In seven dogs, the postprandial SMV %HbO2 increased an average of 2.5% +/- 0.8 before surgery and decreased an average of 6.3% +/- 2.1 when hemodynamically significant (>70%) stenosis of the superior mesenteric artery developed 7-14 days after surgery. In the 10 patients without ischemia, the SMV %HbO2 increased by 4.6% +/- 0.6, whereas in the symptomatic patients a postprandial decrease of 8.8% +/- 0.7 occurred (P < .0001). CONCLUSION: Measurement of the SMV %HbO2 with MR oximetry is a promising test for diagnosis of chronic mesenteric ischemia.

Adult↗

PubMed1997

In vivo target-specific delivery of macromolecular agents with MR-guided focused ultrasound.

Magnetic resonance (MR) images in rabbit muscle were used to select a target region for application of pulsed-focused ultrasound. Liposomes encapsulating gadopentetate dimeglumine, an MR-detectable model representing pharmaceutical agents, were then injected intravenously. Focal enhancement on T1-weighted images, representing gadolinium-liposome accumulation, occurred in the pulsed-focused-ultrasound focal zone. Therefore, MR-guided pulsed-focused ultrasound targeted the delivery of macromolecular pharmaceutical agents within tissues.

Animals↗

PubMed1997

Deep fascial hyperintensity in soft-tissue abnormalities as revealed by T2-weighted MR imaging.

OBJECTIVE: The purpose of this study was to determine whether recently described criteria, including hyperintense T2-weighted signal or other abnormalities revealed by MR imaging within deep fascial planes, are specific for necrotizing soft-tissue infections. MATERIALS AND METHODS: We reviewed 22 MR imaging examinations that revealed abnormally high signal intensity within deep fascial planes on T2-weighted images. Twenty-one of the patients had clinical diagnoses other than necrotizing soft-tissue infection, including nonnecrotizing cellulitis (n = 4), abscess without evidence of necrotizing fasciitis (n = 5), and cellulitis with accompanying vascular thrombosis (n = 2). MR imaging was performed using T1-weighted spin-echo (range of TRs/range of TEs, 300-800/9-30) and fat-saturated T2-weighted fast spin-echo (3000-5000/76-108) sequences. Gadolinium-enhanced T1-weighted spin-echo MR images with fat saturation were obtained for 14 patients. Two reviewers, unaware of clinical diagnoses, evaluated each study for abnormalities in superficial and deep soft tissues and submitted a consensus diagnosis. RESULTS: Using only the described MR imaging criteria, we interpreted all cases as necrotizing cellulitis, including the cases of 21 patients who had nonnecrotizing conditions. CONCLUSION: Hyperintense T2-weighted signal within deep fascial planes and muscle, with or without contrast enhancement, is not specific for necrotizing soft-tissue infection. A variety of conditions exhibited similar findings and were indistinguishable from necrotizing soft-tissue infection.

Adult↗

PubMed1997

Spiral spin-echo magnetic resonance imaging of the pelvis with spectrally and spatially selective radiofrequency excitation: comparison with fat-saturated fast spin-echo imaging.

OBJECTIVE: The authors describe their initial clinical experience in comparing a spiral spin-echo technique with a fat-saturated fast spin-echo technique for imaging the pelvis. METHODS: A total of 18 patients were imaged with both spiral spin-echo and fat-saturated fast spin-echo magnetic resonance imaging. The spiral spin-echo technique combines a spectrally and spatially selective radiofrequency excitation with a spiral k-space trajectory. This technique permits rapid acquisition of T2-weighted water-only images. RESULTS: The spiral spin-echo images were judged superior to the fat-saturated fast spin-echo images in terms of uniformity of fat suppression and absence of flow-related artifacts. However, the overall image quality of the spiral spin-echo images was inferior to that of the fat-saturated fast spin-echo images, as a result of blurring caused by off resonance effects. The two techniques were judged equivalent in terms of conspicuity of the abnormality and diagnostic information. CONCLUSION: The authors conclude that the spiral spin-echo technique holds promise, particularly if combined with a deblurring algorithm.

Adolescent↗

PubMed1996

Diminished postprandial hyperemia in patients with aortic and mesenteric arterial occlusive disease. Quantification by magnetic resonance flow imaging.

BACKGROUND: Superior mesenteric blood flow in the fasting and postprandial state in humans can be measured accurately by cine phase-contrast (CPC) magnetic resonance (MR) imaging. Postprandial flow changes associated with mesenteric arterial occlusive disease (MAOD) are unknown. METHODS AND RESULTS: We used CPC MR imaging to measure fasting and postprandial blood flow in the superior mesenteric artery (SMA) and vein (SMV) in 22 patients (mean age, 69 years) with aortic occlusive disease and MAOD and compared the results with similar measurements in 8 younger, asymptomatic volunteers (mean age, 34 years). All 22 patients had stenosis or occlusion of the splanchnic or pelvic arteries demonstrated by contrast aortography; 19 were asymptomatic and 3 had symptoms of chronic mesenteric ischemia. Mean fasting blood flow was higher in patients (4.5 mL.kg-1.min-1) than in volunteers (2.3 mL.kg-1.min-1; P < .01). However, postprandial hyperemia (mean percentage change in SMV blood flow) was less in the asymptomatic (70%; P < .001) and symptomatic patients (29%; P < .01) than in the volunteers. Postprandial SMV flow was similar to SMA flow in the patients but was significantly greater than SMA flow in the volunteers (P < .005). CONCLUSIONS: Postprandial mesenteric hyperemia is reduced in older patients with MAOD. The role of aging alone has not been determined. Fasting and postprandial flow changes in these patients may predict the onset of chronic mesenteric ischemia.

Adult↗

PubMed1996

MR angiography of abdominal ischemia.

Advances during the past decade in MRI have made this modality increasingly suitable for evaluating abdominal vascular diseases. Preliminary results in canine models and humans suggest that MRI has the potential of becoming a definitive, noninvasive test for the diagnosis of both acute and chronic mesenteric ischemia. MRI can provide both morphological information about the patency or degree of stenosis in mesenteric vessels as well as quantitative functional information such as blood flow and blood oxygen saturation in these vessels. The MR techniques developed for studying the mesenteric circulation also can be used for improving the diagnosis and posttreatment evaluation of vascular diseases in other abdominal organ systems.

Acute Disease↗

PubMed1996

Adaptations of ligamentum teres in ischemic necrosis of human femoral head.

Little is known about the biomechanical properties of human ligamentum teres. To more fully understand the ligamentum teres, its dimensions and mechanical properties were measured in 22 cases of acute fracture of the femoral neck and 21 cases of ischemic necrosis of the femoral head. The specimens first were preconditioned and then loaded to failure with a testing machine at a fast strain rate of 100% s(-1). The ischemic necrosis group had a significantly larger volume (3.09 +/- 1.81 ml versus 1.30 +/- 0.62 ml) and cross section area (65.3 +/- 59.1 mm2 versus 30.6 +/- 27.2 mm2) than did the acute fracture group. The former also had a significantly greater ultimate load (234 +/- 168 N versus 130 +/- 111 N) and strain energy to failure (1.22 +/- 1.04 J versus 0.41 +/- 0.39 J), but a significantly smaller linear modulus (4.72 +/- 3.31 MPa versus 8.69 +/- 7.97 MPa) than did the latter. Histologic studies showed differences in the amount of organized collagen and components of subsynovial tissue between the 2 groups. Mechanical and morphologic adaptations of the ligamentum teres in a group of ischemic femoral heads are described, and a possible biomechanical role is suggested for the ligamentum teres in the hip joint in conjunction with the ischemic necrosis of the femoral head.

Adaptation, Physiological↗