Search PubMed⌕ Search

Biomedical subjects

R C Nelson

Publications and source records attributed to R C Nelson.

At least 91 records · Page 5Linked to original sources
PubMed1993

Hepatic arterial resistive indices: correlation with the severity of cirrhosis.

Forty-three patients who were scheduled to undergo a percutaneous liver biopsy were evaluated with Doppler sonography to determine the hepatic arterial resistive index (RI). The histologic specimens were graded by a pathologist regarding cirrhosis and inflammation. The specimens demonstrated no cirrhosis in 12 of 43 (28%) patients, early cirrhosis in 10 of 43 (23%), and established cirrhosis in 21 of 43 (49%). Analysis also revealed that inflammation was absent in three of 43 (7%) patients, minimal in seven of 43 (16%), mild in 17 of 43 (40%), moderate in 13 of 43 (30%), and severe in three of 43 (7%). Hepatic artery RIs (without correction for heart rate) ranged from 0.64 +/- 0.06 in patients with early cirrhosis to 0.68 +/- 0.09 in patients with severe inflammation. There was no significant correlation between the degree of cirrhosis and/or inflammation and hepatic artery RI (with or without correction for heart rate). We conclude that Doppler determination of hepatic artery RIs is not a reliable method of predicting the severity of hepatic cirrhosis and/or inflammation.

Biopsy, Needle↗
PubMed1993

Dual contrast enhancement of both T1- and T2-weighted sequences using ultrasmall superparamagnetic iron oxide.

BMS 180549 (previously AMI-227), an ultrasmall superparamagnetic iron particulate agent, was investigated to determine its utility as a contrast agent on T1-weighted, as well as T2-weighted sequences, as a function of route of administration, (intravenous versus selective arterial) and concentration. Twelve farm pigs were divided into three groups of four each by route of administration (intravenous, selective superior mesenteric, or selective hepatic arterial injection). 10 mumol/kg and 20 mumol/kg dosages were given and evaluated both immediately after and 20-24 hr after contrast infusion, using both spin-echo and gradient-echo T1 and T2-weighted sequences. Significant postcontrast liver and spleen enhancement was noted at both concentrations, regardless of route of administration on both T1- and T2-weighted sequences. The earliest postcontrast T1-weighted sequence obtained during the 1-3 min interval following IV administration of high dose (20 mumol/kg) contrast demonstrated an average of +42.8% liver and +249.0% spleen enhancement; 24 hr later this decreased to 0 and 7.2%, respectively. The earliest postcontrast T2-weighted sequence obtained during the 8-17 min interval post high-dose IV contrast showed an average of -75.8% decrease in liver and -28.7% decrease in spleen signal intensity; 24 hr later the magnitude of these changes diminished to -33.1% and +2.5%, respectively. No significant difference was noted in liver or spleen enhancement, regardless of route of contrast administration (intravenous versus intraarterial).

Animals↗
PubMed1993

Magnetic resonance imaging after arterial portography with manganese dipyridoxal diphosphate.

RATIONALE AND OBJECTIVES: The authors assess performing hepatic magnetic resonance imaging (MRI) after arterial portography with manganese dipyridoxal diphosphate (MnD-PDP), a hepatobiliary contrast agent, as an invasive but potentially highly sensitive means of focal lesion detection. METHODS: Eight pigs underwent superior mesenteric artery catheterization and injection of 10 mumol/kg MnDPDP. Magnetic resonance imaging at 1.5 T (SE-140/10) was performed before, then at 15 and 30 minutes after injection. Seven or more days later, the same MRI protocol was performed after intravenous injection of 10 mumol/kg MnDPDP. RESULTS: Fifteen minutes after intra-arterial injection, enhancement of the liver predominated (86 +/- 13%), followed by the renal cortex (44 +/- 14%), pancreas (26 +/- 9%), and spleen (14 +/- 9%). At 30 minutes, enhancement of renal cortex significantly increased (50 +/- 14%). There was no significant difference in enhancement of the liver, spleen, pancreas, or renal cortex when we compared intra-arterial and intravenous administration. CONCLUSION: After the injection of 10 mumol/kg MnDPDP into the superior mesenteric artery of pigs there is no significant difference in visceral organ enhancement compared to intravenous administration. The data suggests that the hepatocyte binding sites may be overwhelmed by this dose and/or injection rate of MnDPDP.

Animals↗
PubMed1993

Combined CT arterial portography and CT hepatic angiography for evaluation of the hepatic resection candidate. Work in progress.

PURPOSE: To determine whether the addition of computed tomographic (CT) angiography to CT arterial portography would improve lesion detection and heighten confidence in interpreting perfusion abnormalities. MATERIALS AND METHODS: The two examinations were performed sequentially in 10 candidates for surgical resection of hepatic tumors. Arterial vascular access was obtained with bilateral punctures of the common femoral artery and selective placement of angiographic catheters in the hepatic artery and superior mesenteric artery (SMA). CT scans were obtained first during injection of contrast material into the SMA, followed by repeated imaging of the liver during injection of contrast material into the hepatic artery. RESULTS: The procedure demonstrated, among other results, three additional lesions in two patients, a possibly nontumorous abnormality as tumorous in one, and a suspected tumorous abnormality as nontumorous in one. Suspected nontumorous abnormalities in four patients were confirmed at CT angiography. CONCLUSION: These preliminary data support a trial of this technique in a larger population.

Adolescent↗
PubMed1993

Splenic venous flow exceeding portal venous flow at Doppler sonography: relationship to portosystemic varices.

OBJECTIVE: The purpose of this study was to determine if the Doppler sonographic finding of hepatopetal flow in the splenic vein that exceeds hepatopetal flow in the portal vein is associated with portosystemic varices. MATERIALS AND METHODS: Sixty-four patients with chronic liver disease were studied retrospectively. In 32 patients, splenic venous flow exceeded portal venous flow (S > P group); in 32 patients, portal venous flow exceeded splenic venous flow (P > S group). All patients were evaluated with Doppler sonography and CT of the upper part of the abdomen. Upper endoscopy was performed within 3 months of sonography in 44 of the 64 patients. RESULTS: In the S > P group, mean splenic volume was significantly larger (p = .02) than in the other group. The prevalence of varices as determined by CT in the esophageal, coronary, and peripancreatic regions was also higher in this group (p < or = .01). When esophageal varices were present, they were judged on the basis of their CT appearance to be massive in 50% of the S > P group and in 0% of the P > S group. Upper endoscopy revealed esophageal varices in 92% of the S > P group and in 55% of the P > S group (p < .005). Bleeding esophageal varices were noted in 75% of the S > P group and in 30% of the P > S group (p < .01). CONCLUSION: Patients with chronic liver disease and the Doppler sonographic finding of splenic venous flow that exceeds portal venous flow have an increased prevalence of portosystemic varices, which tend to be larger and more likely to bleed.

Adolescent↗
PubMed1993

Vestibular ontogeny: measuring the influence of the dynamic environment.

In comparison to other special senses, we are only meagerly informed about the development of vestibular function and the mechanisms that may operate to control or influence the course of vestibular ontogeny. Perhaps one contributing factor to this disparity is the difficulty of evaluating vestibular sense organs directly and noninvasively. The present report describes a recently developed direct noninvasive vestibular function test that can be used to address many basic questions about the developing vestibular system. More particularly, the test can be used to examine the effects of the dynamic environment (e.g. gravitational field and vibration) on vestibular ontogeny.

Acceleration↗
PubMed1992

Clinical pharmacology training at the Food & Drug Administration.

Challenged with the clearly demonstrated need for highly trained clinical pharmacologists for new drug development and review activities, the FDA Center for Drug Evaluation and Research (CDER) established an internal Staff College. This organizationally unique and innovative unit addressed the educational needs of both the new and the veteran CDER scientists. A multileveled strategy was conceptualized and implemented as described.

Curriculum↗
PubMed1992

Fast spin-echo imaging of the abdomen during breath-holding: an alternative to RASE and other fast imaging techniques.

We have developed a rapidly acquired T1-weighted spin-echo pulse sequence that uses gradient echo-like parameters of TR 70 ms, TE 10 ms, NEX-1 (SE 70/10/1) with large pulse angles, and presaturation. This sequence yields two images of the abdomen during a comfortable breath-hold of 9 s. Preliminary phantom studies with this sequence demonstrated that peak signal-to-noise ratios occurred at pulse angles of 120 degrees and 135 degrees. Compared to this rapidly acquired sequence, a conventional T1-weighted spin-echo sequence of TR 140 ms, TE 10 ms, NEX-4 demonstrated 2.8 times the signal-to-noise ratio, 2.6 times the liver-spleen contrast-to-noise ratio but only 1.6 times the contrast-to-artifact ratio. When normalized for the imaging time, however, there was little difference in the signal-to-noise and contrast-to-noise ratios, although the SE 70/10/1 demonstrated 2.0 times the contrast-to-artifact ratio. We conclude that for abdominal imaging the SE 70/10/1 is an excellent alternative to RASE and other fast imaging techniques, and, although there are inherently low signal-to-noise ratios, it may be particularly useful when coupled with a paramagnetic contrast agent.

Abdomen↗
PubMed1992

Recovery of vestibular function following hair cell destruction by streptomycin.

Can the vestibular periphery of warm-blooded vertebrates recover functionally from severe sensory hair cell loss? Recent findings in birds suggest a mechanism for recovery but in fact no direct functional evidence has been reported. We produced vestibular hair cell lesions using the ototoxic agent streptomycin sulfate (600 mg/kg/day, 8 days, chicks, Gallus domesticus). Compound action potentials of the vestibular nerve were used as a direct measure of peripheral vestibular function. Vestibular thresholds, neural activation latencies and amplitudes were documented. Eight days of drug treatment elevated thresholds significantly (P < 0.001) and eliminated all but remnants of vestibular activity. Virtually complete physiological recovery occurred in all animals studied over a period of 70 days following treatment. Thresholds recovered within two weeks of drug treatment whereas the return of response morphologies including activation latencies and amplitudes required an additional 6-8 weeks.

Action Potentials↗
PubMed1992

CT during arterial portography: diagnostic pitfalls.

Computed tomography (CT) during arterial portography (CTAP) is an important technique for evaluating the liver before hepatic tumor resection. With this technique, most tumors are of low attenuation compared with that of enhancing parenchyma. At times, low-attenuation lesions are encountered that represent perfusion abnormalities rather than tumor deposits. These perfusion abnormalities can be categorized as (a) those resulting from improper technique; (b) those extending from hilum to capsule (straight-line sign), with or without an obstructing mass; (c) perihilar and periligamentous abnormalities; (d) subcapsular defects (linear or wedge shaped); and (e) those seen with cirrhosis or regenerating nodules. Adjuvant use of delayed CT, magnetic resonance imaging, and intraoperative ultrasound aids in characterization of these nontumorous defects, thereby improving specificity. The authors conclude that when potential candidates are evaluated for hepatic tumor resection, knowledge of the existence of the various diagnostic pitfalls of CTAP and their imaging characteristics is imperative to avoid inadvertent false results.

Angiography, Digital Subtraction↗
PubMed1992

Peritoneal carcinomatosis: preoperative CT with intraperitoneal contrast material.

Thirty-five abdominal computed tomographic (CT) scans of 27 patients with peritoneal metastases from a mucin-producing tumor of the appendix, colon, small bowel, or ovary were retrospectively reviewed. Fifteen scans were obtained of 15 patients after CT with intraperitoneal infusion of contrast material (IP), and 20 scans were obtained of 16 patients with CT without IP. Subsequent exploratory laparotomy revealed that all 27 patients had multi-focal spread of peritoneal metastases. The sensitivity of CTIP and CT without IP for detection of peritoneal metastases at all sites of involvement was 61% and 59%, respectively. For CTIP, the highest sensitivity was in the right subphrenic space (88%), splenic hilum (86%), and left subphrenic space (83%). For CT without IP, the highest sensitivity was noted in the splenic hilum (100%), left subphrenic space (75%), and left paracolic gutter (75%). CTIP and CT without IP had low sensitivity for detection of disease in the greater omentum (50% each) and small-bowel mesentery (38% and 59%, respectively), two areas that had the highest frequency of metastases.

Appendiceal Neoplasms↗
PubMed1992

The frequency and significance of small (less than or equal to 15 mm) hepatic lesions detected by CT.

The purpose of our study was to determine the frequency of detection of small hepatic lesions (less than or equal to 15 mm) in outpatients who had abdominal CT and to assess the significance of these lesions in the presence or absence of known malignant tumors. Contrast-enhanced abdominal CT scans in 1454 patients were reviewed. In 254 patients (17%), hepatic lesions 15 mm or smaller were detected. In 51% of these patients, lesions were judged benign on the basis of other imaging studies, biopsy results, or stability for at least 6 months as shown by CT. Lesions were judged malignant on the basis of progression seen on radiologic studies or biopsy in 22%. The other 27% of the patients had lesions that could not be classified. The majority of patients with small hepatic lesions (82%) were known to have a malignant tumor; in 51% of these patients, lesions were diagnosed as benign. No patient without a known malignant tumor had a small hepatic lesion that was determined to be malignant. Multiple small lesions were more likely to represent malignant disease than were single small lesions. We conclude that small hepatic lesions are common (seen in 17% of our patients), and that there is a high probability that hepatic lesions smaller than 15 mm are benign, even in patients known to have an extrahepatic malignant tumor.

Humans↗
PubMed1992

Persistence of portosystemic collaterals and splenomegaly on CT after orthotopic liver transplantation.

OBJECTIVE: The appearances of portosystemic collaterals and splenomegaly on CT before and after liver transplantation were evaluated. MATERIALS AND METHODS: The records of 54 patients undergoing liver transplantation during a 2.5-year period were reviewed retrospectively. Twenty-five of these patients, in whom both a preoperative abdominal CT scan and a follow-up CT scan at least 1 year after transplantation had been obtained, were clinically well and had had no significant episodes of rejection, severe recurrent hepatitis, or other complication at the time of study. A total of 94 abdominal CT scans in these patients were reviewed to assess changes in portosystemic collaterals and splenic volume. RESULTS: At 6 months after transplantation, portosystemic collaterals at one or more sites were seen in 14 (74%) of the 19 patients scanned at this time in whom collaterals had been seen on CT preoperatively. At 1 year after transplantation, splenic hilar collaterals persisted in 64% of patients, splenocolic ligament collaterals in 50%, retroperitoneal collaterals in 38%, and peripancreatic collaterals in 38% of patients with preoperative varices at these sites who were examined with CT at this interval. Splenic hilar, coronary, and retroperitoneal collaterals were found to persist for up to 4 years after transplantation in the single patient examined at that time. Splenic volume decreased in 94% of patients examined after transplantation, with a mean reduction of 60 +/- 19%. However, the spleen remained significantly enlarged in 56% of patients. CONCLUSION: We conclude that portosystemic collaterals and splenomegaly frequently persist after liver transplantation, but that this finding need not indicate recurrence of hepatic disease or other posttransplantation complications.

Adult↗
PubMed1992

The use of transcutaneous electrical nerve stimulation during the biliary lithotripsy procedure.

Transcutaneous electrical nerve stimulation (TENS) has been suggested as a means to reduce the amount of intravenous analgesia/sedation in patients undergoing extracorporeal shock wave lithotripsy (ESWL). A retrospective analysis of 79 ESWL procedures on 73 consecutive unselected patients was done in an attempt to determine the effectiveness of TENS in reducing the amount of intravenous fentanyl citrate and/or midazolam HCl needed to control pain and anxiety during the ESWL procedure. The study was divided into two parts: (1) all patients receiving TENS (n = 44) versus a non-TENS group (n = 35), and (2) comparison of the early (n = 22) and late non-TENS (n = 22) groups against each other; separately the late non-TENS group was compared to the entire TENS group. In the study, TENS reduce the amount of fentanyl citrate needed to control anxiety by 22.9% (P less than 0.025). No difference was noted when the early and late non-TENS group of patients were compared to each other. A gender difference was noted with a significant reduction in the dose of fentanyl citrate only in female patients receiving TENS (45.4%). Likewise, there was a significant reduction in the dose of midazolam HCl only in males who had TENS (38.9%). The data suggests that TENS may be a useful addition to reduce the amount of sedation and analgesia during ESWL.

Adult↗
PubMed1991

Visual homing using an associative memory.

Homing is the process by which an autonomous system guides itself to a particular location on the basis of sensory input. In this paper, a method of visual homing using an associative memory based on a simple pattern classifier is described. Homing is accomplished without the use of an explicit world model by utilizing direct associations between learned visual patterns and system motor commands. The method is analyzed in terms of a pattern space and conditions obtained that allow the system performance to be predicted on the basis of statistical measurements on the environment. Results of experiments utilizing the method to guide a robot-mounted camera in a three-dimensional environment are presented.

Animals↗
PubMed1991

Magnetic resonance imaging of the pancreas with gadolinium-DTPA.

Gadolinium (Gd)-DTPA was evaluated as a contrast agent for magnetic resonance (MR) imaging of the pancreas at 1.5T. Twenty-five patients were imaged with identical gradient-echo (GE) (TR 47, TE 13, 80 degree pulse angle) and spin-echo (SE) (TR 300, TE 15) MR sequences prior to and following an intravenous bolus of 0.1 mmol/kg Gd-DTPA. Marked pancreatic enhancement was demonstrated on dynamic sequential breath-hold GE images obtained immediately following the Gd-DTPA bolus (116% mean enhancement over pre-Gd-DTPA images). Enhancement decreased but persisted on the SE images obtained approximately 5 and 15 min following the Gd-DTPA bolus (65 and 60% mean enhancement, respectively). Five of the patients had a pancreatic mass. In these five patients, the enhancement of pancreatic tissue resulted in improved conspicuity of the mass. These initial results suggest that pancreatic enhancement occurs following an intravenous bolus of Gd-DTPA and has the potential to improve MR visualization of pancreatic masses.

Adenocarcinoma↗