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Biomedical subjects

K Oda

Publications and source records attributed to K Oda.

690 records · Page 39Linked to original sources
PubMedDate not supplied

Diagnostic pitfalls of MR cholangiopancreatography in the evaluation of the biliary tract and gallbladder.

Magnetic resonance (MR) cholangiopancreatography is a noninvasive imaging technique that has proved accurate in the diagnosis of biliary obstruction. However, various diagnostic pitfalls have been reported with MR cholangiopancreatography that were not encountered previously at conventional biliary imaging. These pitfalls may simulate or mask various pathologic conditions of the extrahepatic bile duct or main pancreatic duct and may be caused by a variety of factors. Because of its postprocessing nature, maximum-intensity-projection reconstruction may mask a small gallstone if the stone is surrounded by hyperintense bile and may cause false ductal disconnection or duplication when a breath hold is not performed perfectly. Extraductal factors (e.g., metallic surgical clips, intravascular metallic coils, gas in the stomach or duodenum) can cause signal loss in the adjacent part of the extrahepatic bile duct, which may in turn lead to a false-positive diagnosis of ductal narrowing or obstruction. Normal vascular structures including the right hepatic and gastroduodenal arteries can cause pseudo-obstruction of the extrahepatic bile duct by pulsatile compression. Intraductal factors (e.g., gas, hemorrhage, debris, iodinated contrast material) reduce the signal intensity of the bile, which may result in pseudo-obstruction, false filling defects, or a nonvisualized gallbladder or bile duct. Knowledge of the existence and high prevalence of these diagnostic pitfalls should help prevent misinterpretation of MR cholangiopancreatograms.

Artifacts↗
PubMedDate not supplied

Contrast-enhanced three-dimensional MR portography.

Three-dimensional (3D) magnetic resonance (MR) portography with contrast material enhancement is a fast means of evaluating the portal venous system that has some advantages over currently used modalities, such as digital subtraction angiography, helical computed tomography, ultrasonography, and nonenhanced MR angiography with time-of-flight and phase-contrast techniques. With contrast-enhanced 3D MR portography, a first-pass study of the mesenteric vasculature is performed after rapid bolus injection of gadopentetate dimeglumine; a 3D fast field echo sequence is used, which can demonstrate the intrahepatic and extrahepatic portal venous system clearly. Repeated sequences after administration of gadopentetate dimeglumine allow separate demonstration of the splanchnic arteries and portomesenteric veins. The images are reconstructed by means of maximum-intensity projection postprocessing, and a subtraction technique can be used to eliminate arterial enhancement and demonstrate portosystemic shunts. The coronal source images simultaneously demonstrate parenchymal lesions of the liver, pancreas, biliary tract, and spleen. This technique is clinically indicated in portosystemic shunt, portal vein thrombosis, hepatocellular carcinoma, pancreatobiliary tumor, hepatic vein obstruction, differentiation of splanchnic arterial from portal venous disease, and gastrointestinal hemorrhage. Its limitations include allergic reactions to contrast media, inappropriate positioning of the 3D acquisition slab, respiratory motion artifacts, and pseudodissection.

Contrast Media↗
PubMedDate not supplied

Dynamic subtraction contrast-enhanced MR angiography: technique, clinical applications, and pitfalls.

Rapid advances in techniques of contrast material-enhanced magnetic resonance (MR) angiography have enabled evaluation of the entire aorta and the main arteries. Dynamic subtraction MR angiography consists of first-pass imaging of long segments of arteries by using a three-dimensional fast field echo sequence with multiple rapid bolus injections of a small dose of gadopentetate dimeglumine. Subtraction enables clear demonstration of the enhanced vascular lumen by eliminating background signal. Improved temporal resolution and repeated sequences after gadopentetate dimeglumine administration allow demonstration of arteries and veins separately. Double subtraction postprocessing can be used to eliminate arterial enhancement in demonstration of the portal and systemic veins. Additional postprocessing can be used to demonstrate arteries in a single image in patients with aortic dissection or a prolonged circulation time. To optimize the examination, the pulse sequence, injection dose, injection rate, timing of the start of data acquisition, imaging time, breath holding, section thickness, and coil selection should be considered. This technique is flexible enough to be applied in a variety of clinical settings, including atherosclerotic occlusive disease, aneurysm of aortoiliac arteries, bypass graft, Takayasu arteritis, aortic dissection, antiphospholipid antibody syndrome, renal artery disease, pelvic vascular disease, and the portomesenteric venous system.

Contrast Media↗
PubMedDate not supplied

Stimulus induced repetitive muscle potentials in the gracile axonal dystrophy (GAD) mouse.

Gracile axonal dystrophy (GAD) is an inherited neurodegenerative disease in the mouse with progressive sensory ataxia and motor paresis. Electromyographic examination was conducted in 25 unanaesthetized GAD mice and 24 controls of the same strain during 6, 9 and 12 wk of postnatal life. Among 9 and 12 wk old mice, about 75% showed resting spontaneous activities--either fibrillation or fasciculation or both. On stimulation of the tibial nerve at ankle, with single pulse, the EMG showed repetitive muscle potentials of large amplitude, following "M" response. The frequency and duration of the train of these stimulus--induced repetitive muscle potentials (SIRMP) were almost constant in a given animal. The SIRMP failed to reappear in response to the second stimulus within 5 s when twin pulses were applied or within 5 min when tetanic stimuli were applied, indicating their fatigability. It is concluded that the SIRMP originate from immature, supplementary motor endplates that develop at ultraterminal nerve sproutings induced by denervation and reinnervation and possibly are due to hyperexcitable trigger points in the peripheral nerve endings. The EMG abnormalities in the GAD mouse are very much similar to those observed in human syndromes with hyperexcitable peripheral nerves that result in sustained muscle activity like neurotonia and hence the GAD mouse is a good model of such motor abnormalities in man.

Action Potentials↗
PubMedDate not supplied

Preoperative natural killer cell activity: correlation with distant metastases in curatively research colorectal carcinomas.

The authors investigated whether host immunity contributes to the development of asynchronous distant metastases in colorectal carcinomas. The host immunity was examined 8 times, pre- and postoperatively during a one year period in 77 curatively operated cases. A prospective study was performed using obtained personal data. During the mean follow-up period of 920 days, 13 patients developed distant metastases. Among the immunological parameters, the preoperative natural killer (NK) cell activity differed significantly between the metastases positive and negative groups. On univariate analysis, dichotomous NK activity, presence of nodal metastases, and venous invasion correlated with metastases. The hazard ratios on multivariate analysis were 4.53, 3.82, and 4.81, respectively. No correlation was noted between NK activity and the progression stages of colorectal carcinomas. These data suggested that attenuated preoperative NK activity is an important background factor for the development of asynchronous distant metastases following curative resection of colorectal carcinomas.

Aged↗