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Biomedical subjects

R C Nelson

Publications and source records attributed to R C Nelson.

At least 127 records · Page 7Linked to original sources
PubMed1989

Assessing sincerity of effort in maximal grip strength tests.

The measurement of maximum hand grip strength in ergonomic or clinical settings has been a useful means of assessing physical characteristics, progress in rehabilitation and degree of disability in upper extremity injuries. The validity of the peak forces observed in such measurements is compromised by the requirement of subject cooperation in giving a maximum effort. Thus, an easily administered analysis of subject sincerity would improve this basic strength-testing tool. Several variables were developed for the discrimination of faking (submaximal) from sincere (maximal) grip contractions. A microcomputer-based grip force data collection system was assembled in which analog output from a Jamar hand dynamometer was sampled at 200 Hz and digitally analyzed. A total of 43 normal subjects (20 male, 23 female) were tested under sincere and faking conditions (three trials of each condition for each hand). The force-time curves of each trial were analyzed for peak and average forces and force variability. From these basic parameters five discriminator variables were developed. The frequency distribution of the sincere values for each of these variables was used to determine a criterion value for discrimination of sincere from faking trials. The five discriminators correctly detected 95.0, 92.5, 100, 100 and 97.5% of the male faking trials. Female faking was less successfully detected: 59.7, 52.2, 78.3, 71.7 and 87.0% correct detection resulted for the variables (with a 95% confidence level of correctly identifying sincerity). Multiple variable predictions improved the female faking detection up to 93.5% with little apparent decrement in sensitivity to sincerity identification.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Hand-held electronic teaching-aid for demonstrating MRI concepts.

We describe a hand-held electronic teaching-aid for magnetic resonance imaging (MRI), which can be used to demonstrate the dependence of signal intensity on changing pulse sequence parameters (TR and TE), the dependence of intensity on changing tissue parameters (T1 and T2), and the ideas of "T1-weighting" and "T2-weighting" as they relate to image contrast. The device was specifically designed to be easy to use and readily accessible to residents-in-training and MR neophytes.

Electronics↗
PubMed1989

Hepatic tumors: comparison of CT during arterial portography, delayed CT, and MR imaging for preoperative evaluation.

Forty-three patients with known primary or secondary neoplastic involvement of the liver underwent evaluation to determine the number, size, and location of focal lesions before possible tumor resection. Imaging studies included computed tomography (CT) during arterial portography (CTAP), delayed CT, and magnetic resonance (MR) imaging at various pulse sequences. Results of radiologic studies were compared with surgical and pathologic findings. In the combined group of surgical and nonsurgical patients, CTAP was significantly more sensitive (85%) than all other techniques except 1.5-T T2-weighted spin-echo imaging (64%). Combining the information from all MR pulse sequences yielded a cumulative sensitivity of 68%. Combining the information from two modalities yielded sensitivity of 96% for CTAP plus MR imaging, 85% for CTAP plus delayed CT, and 77% for delayed CT plus MR imaging. The authors conclude that when it is vital to know the precise number, size, and location of focal hepatic lesions before tumor resection, CTAP has the highest sensitivity, but MR imaging is an important adjuvant.

Adult↗
PubMed1989

Contrast-enhanced CT of the liver and spleen: comparison of ionic and nonionic contrast agents.

We conducted a randomized, blinded, prospective study evaluating hepatic parenchymal density changes during dynamic bolus CT (180 ml of contrast material given IV) and delayed CT (5 hr after 60 g of iodine) in order to compare the enhancement characteristics of an ionic contrast agent (iothalamate-60) and two nonionic agents (iohexol-300 and iopamidol-300). A total of 75 patients with known or suspected cancer were studied (25 patients per contrast agent). After a baseline unenhanced CT scan was obtained, dynamic bolus and delayed CT scans were obtained for all patients with one of the three contrast agents. The density of the liver and spleen was measured in Hounsfield units (H) for unenhanced CT, dynamic bolus CT, and delayed CT. The average percentage of enhancement was calculated as follows: postcontrast density minus precontrast density was divided by precontrast density and then multiplied by 100. For dynamic bolus CT, the average percentage of enhancement of the liver was 105% when iohexol-300 was used, 98% when iopamidol-300 was used, and 83% when iothalamate-60 was used. No significant difference was seen between the postcontrast enhancement of the three contrast agents on dynamic bolus CT scans (p greater than .05). For delayed CT, the average percentage of enhancement of the liver was 34% when iothalamate-60 was used, 28% when iopamidol-300 was used, and 16% when iohexol-300 was used. Both iothalamate-60 and iopamidol-300 showed superior enhancement on delayed CT, compared with iohexol-300 (p = .0001). We conclude that for dynamic bolus CT, all three contrast agents are similar, with no statistically significant differences in postcontrast enhancement of the liver. For delayed CT, however, hepatic enhancement with iothalamate-60 and iopamidol-300 is statistically superior to that with iohexol-300.

Adult↗
PubMed1989

Portal venous gas after hepatic transplantation: sonographic detection and clinical significance.

In seven (18%) of 39 liver transplantation patients, serial Doppler sonographic examinations performed in the first 2 weeks after the transplantation showed transient, highly echogenic nonshadowing particles moving within the portal vein, believed to be portal venous air. This finding was associated with sepsis in one patient, a positive stool culture for Clostridium difficile in another, and postoperative ileus in a third patient. A fourth patient had primary graft failure and required a second transplant. No potential cause was found in the other three patients. None of the patients had bowel infarction or necrosis. The finding was not associated with transplant rejection or graft infection. We conclude that the sonographic finding of portal venous gas is common in the first 2 weeks after hepatic transplantation and may not have grave prognostic significance.

Adolescent↗
PubMed1989

Renal corticomedullary junction. Performance of T1-weighted MR pulse sequences.

Inability to demonstrate the renal corticomedullary junction (CMJ) on magnetic resonance (MR) images has been reported in connection with several medical renal diseases. T1-weighted spin echo pulse sequences have been advocated to demonstrate a signal intensity difference between cortex and medulla. This study was undertaken to determine which of several T1-weighted spin echo (SE) and gradient echo (GE) sequences are better for delineation of the CMJ. The MR studies were performed at 0.5 Tesla on 27 normal volunteers. Multi-slice axial images of both kidneys were obtained in all subjects at each of the following five pulse sequences: SE 250/20, SE 500/30, SE 900/30, and GE 300/15 with 80 degrees and 64 degrees flip angles. Contrast/noise ratios were calculated for the signal intensity differences between cortex and medulla; the average standardized contrast/noise ratios ranked as follows: GE 300/15/80 degrees = 3.01 +/- 0.74, GE 300/15/64 degrees = 2.72 +/- 0.74, SE 250/20 = 2.02 +/- 0.33, SE 500/30 = 1.96 +/- 0.51, and SE 900/30 = 1.71 +/- 0.39. In addition, the five sequences for each patient were randomized and the images were independently ranked for delineation of CMJ by three MR radiologists. The cumulative subjective ranking for all observers from best to worst is as follows: SE 500/30, GE 300/15/80 degrees, GE 300/15/64 degrees, SE 900/30, SE 250/20. Although better contrast/noise ratios are achieved with the GE sequences and the more T1-weighted SE sequences, as a practical matter this does not seem to be the only significant factor when compared with the visual image evaluation by independent observers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Finding motion parameters from spherical motion fields (or the advantages of having eyes in the back of your head).

A theory is developed for determining the motion of an observer given the motion field over a full 360 degree image sphere. The method is based on the fact that for an observer translating without rotation, the projected circular motion field about any equator can be divided into disjoint semicircles of clockwise and counterclockwise flow, and on the observation that the effects of rotation decouple around the three equators defining the three principal axes of rotation. Since the effect of rotation is geometrical, the three rotational parameters can be determined independently by searching, in each case, for a rotational value for which the derotated equatorial motion field can be partitioned into 180 degree arcs of clockwise and counterclockwise flow. The direction of translation is also obtained from this analysis. This search is two dimensional in the motion parameters, and can be performed relatively efficiently. Because information is correlated over large distances, the method can be considered a pattern recognition rather than a numerical algorithm. The algorithm is shown to be robust and relatively insensitive to noise and to missing data. Both theoretical and empirical studies of the error sensitivity are presented. The theoretical analysis shows that for white noise of bounded magnitude M, the expected errors is at worst linearly proportional to M. Empirical tests demonstrate negligible error for perturbations of up to 20% in the input, and errors of less than 20% for perturbations of up to 200%.

Humans↗
PubMed1988

Focal hepatic lesions: detection by dynamic and delayed computed tomography versus short TE/TR spin echo and fast field echo magnetic resonance imaging.

Eighteen patients with focal hepatic lesions were evaluated with two computed tomographic (CT) techniques including dynamic sequential bolus contrast CT and delayed contrast CT, and 3 magnetic resonance (MR) techniques including a spin echo pulse sequence with TE/TR of 21/310 msec and 2 fast field echo sequences using a TE/TR of 15/300 msec and 80 degrees flip angle (T1-weighted) and TE/TR of 15/500 msec and 10-20 degrees flip angle (T2-weighted). We concluded that CT, using delayed contrast and dynamic sequential bolus contrast techniques, was consistently superior to the 3 MR pulse sequences used on our imagers in terms of number of lesions detected, lesion-to-liver contrast, and quality of scan.

Adult↗
PubMed1988

Role of computed tomography in screening for hepatocellular carcinoma in patients with cirrhosis.

One hundred patients with cirrhosis underwent abdominal computed tomography (CT) using a delayed contrast technique to determine liver and spleen volume. These scans were reviewed to screen this "at risk" population for hepatocellular carcinoma (HCC). Fifteen of the 100 screened patients had focal abnormalities suspicious for HCC. On biopsy, only 1 patient was shown to have HCC. The other 14 patients had either fatty infiltration or focal regeneration. In the same time interval, a total of 10 patients had histologically proven HCC. All presented with symptoms and died within 4 months of diagnosis. The results show that focal hepatic lesions can be detected by CT but in this population the lesions may not be due to HCC. The incidence of HCC was approximately 1%, probably reflecting a truly low incidence in this population.

Biopsy↗
PubMed1988

Delayed magnetic resonance hepatic imaging with gadolinium-DTPA.

Magnetic resonance imaging of the liver was performed on 11 rabbits (3-5 kg) before and at 4, 5 and 6 hours after the intravenous administration of 0.3 mM/kg Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) to determine if hepatocytes exhibit delayed excretion of Gd-DTPA, similar to the delayed hepatic excretion of iodinated contrast agents. Imaging was performed at 0.5 Tesla in the axial plane using a spin echo sequence of TR/TE, 250/20 milliseconds. Precontrast and postcontrast intensity changes for liver and muscle were standardized and compared over time. The average percent of postcontrast enhancement for liver and muscle, respectively was: 30.6 +/- 9.5% and 17.3 +/- 17.0% immediately postcontrast; 9.7 +/- 13.6% and 1.6 +/- 13.8% at 4 hours; 9.6 +/- 7.8% and 4.3 +/- 13.2% at 5 hours; and 11.0 +/- 7.8% and 4.1 +/- 11.7% at 6 hours. We conclude that there is not significant hepatocyte excretion of Gd-DTPA at 4 to 6 hours postcontrast injection in rabbits and that this may not be an advantageous paramagnetic contrast strategy for focal hepatic lesion detection.

Animals↗
PubMed1988

Anergy testing in nursing home residents.

Delayed cutaneous hypersensitivity (DCH) testing is commonly used to determine exposure to Mycobacterium tuberculosis and in the evaluation of cellular-mediated immunity. Many reports indicate that anergy to ubiquitous antigens is common in the elderly. Recent studies suggest that anergy in the aged is not common when five or more antigens are used. Because it is often difficult to purchase singularly or apply a larger number of quality DCH antigens, we investigated the usefulness of the Multitest CMI in 29 nursing home residents with chronic diseases. This device simultaneously applies seven skin test antigens and a negative control. Ten young healthy subjects served as controls. DCH reactions were scored based on the sum of induration and total number of positive responses. Although elderly subjects had significantly lower scores than the young subjects, only 7% of elderly subjects were anergic. Our data indicate that the Multitest CMI is a highly effective device to test for DCH in geriatric subjects with chronic diseases. Although skin test responses in these subjects were blunted, in most residents cellular-mediated immunity remained intact.

Adult↗
PubMed1988

Adrenal masses: characterization with T1-weighted MR imaging.

The ability of a T1-weighted spin-echo magnetic resonance (MR) sequence to allow differentiation of benign from malignant adrenal masses at 0.5 T was investigated in 28 patients with 35 adrenal masses. All nine lesions with an adrenal mass-liver signal intensity ratio of 0.71 or less were metastases, and all 15 with a ratio of 0.78 or more were adenomas. Eleven masses (31%)--including six adenomas, three metastases, a pheochromocytoma, and a neuroblastoma--had ratios between these values. Nine of ten masses with adrenal mass-fat intensity ratios of 0.35 or less were metastases, and all 12 with ratios of 0.42 or more were benign. Eleven masses (31%), four malignant and one benign, had ratios between these values. The ratios for two masses could not be calculated due to lack of fat. The specificity of T1-weighted MR imaging in differentiating benign from malignant adrenal masses appears similar to that reported for T2-weighted imaging. However, significant overlap occurred, as has also been reported for T2-weighted imaging. While both imaging sequences may help distinguish benign from malignant adrenal masses in some cases, biopsy is still necessary when an accurate histologic diagnosis is essential.

Adenoma↗
PubMed1988

Liver and abdominal screening in patients with cancer: CT versus MR imaging.

A prospective multiinstitutional study was performed to compare the ability of dynamic sequential contrast material-enhanced computed tomography (CT), delayed contrast material-enhanced CT, and two T1-weighted magnetic resonance (MR) sequences (spin echo and inversion recovery) to demonstrate metastatic disease in the liver and abdomen in patients with cancer. All four techniques had comparable rates of hepatic lesion detection when compared individually or when the combined CT techniques were compared with the combined MR techniques. The sensitivity to hepatic disease was 96% (27 of 28 patients) for the combined MR techniques versus 93% (26 of 28 patients) for the combined CT techniques. However, CT was statistically superior in the detection of extrahepatic disease, with significant extrahepatic findings demonstrated by CT in only 12 of 59 patients (20%). For this reason, the authors continue to recommend CT in the initial screening of patients with cancer for upper abdominal metastatic disease.

Abdominal Neoplasms↗
PubMed1988

Drug safety, pharmacoepidemiology, and regulatory decision making.

The safety or risk assessment of a pharmacotherapeutic agent begins early in its development and continues throughout its use cycle. The practice of pharmacoepidemiology is the art of using the sciences and the tools of science to generate information about pharmaceutical outcomes, including associated risks, in the postmarketing environment. A pharmacoepidemiologist must be capable of functioning with a matrix constructed of three components: a knowledge base, a conceptual framework, and an interpretive framework. From this perspective one can establish surveillance schemes, or understand a posed research question, select strategies, apply methodologies, and interpret the results of purposeful investigations. When conveyed to the risk manager, appropriately interpreted results of a properly conducted risk assessment can be used in regulatory decision making. Seven case studies are presented as examples of this approach.

Decision Making↗
PubMed1988

The shock attenuation role of the ankle during landing from a vertical jump.

Three landing surfaces were used to examine a hypothesized increased shock attenuation role of the ankle with increased damping demands. Eleven male recreational basketball players performed three symmetric barefoot countermovement vertical jumps on each surface. Two externally mounted low mass accelerometers (medial calcaneus and distal anterio-medial tibia), a piezoelectric force platform, and high speed cinematography recorded the landing. Accelerometer signal distortion was corrected through the application of a linear spring/damper model of the accelerometer attachment. The model indicated that raw acceleration data were overestimated 68% at the calcaneal attachment and 8% at the tibial attachment. Peak corrected acceleration at metatarsal contact varied little across landing surfaces, and, across surfaces, mean (SD) peak accelerations of 20.8 (9.3) and 14.3 (3.6) g's were recorded at the calcaneus and tibia, respectively. Peak vertical force and ankle joint motion varied little across the surfaces, suggesting that the entrenched kinematics of landing surpassed the introduced range of surface cushioning. Separation of the data by post-metatarsal contact landing style indicated that seven subjects landed with heel contact, with the remaining four attenuating the impact without heel contact. By avoiding the transient associated with the cessation of downward heel motion, the nonheel contact landers effectively reduced exposure to transients by nearly 50%.

Ankle Joint↗
PubMed1987

Magnetic resonance imaging for detection of arterial and venous occlusion in canine muscle flaps and bowel segments.

Magnetic resonance imaging (MRI) was performed on 16 muscle flaps and eight jejunal segments in dogs to assess its usefulness in detecting vascular occlusion. Arterial or venous occlusion was carried out in 11 muscles and six bowel segments, with the remaining sham flaps serving as controls. Imaging was performed over 2 hours using a spin echo pulse sequence with T2 weighting. Arterial occlusions in muscles resulted in T2 values 15-30% higher than controls, while venous occlusion produced T2 values 55-75% higher than controls. Differences became significant (p less than 0.05) at 10 minutes after venous occlusion and at 35 minutes after arterial occlusion. Differences between occluded and control bowel segments, although demonstrating a similar trend, failed to reach statistical significance in this preliminary study. The authors conclude that magnetic resonance imaging may be a valuable method for early detection of venous and arterial occlusion in muscle flaps. Further study may also demonstrate this technique to be useful in the diagnosis of ischemic bowel.

Animals↗
PubMed1987

Renal allograft rejection: evaluation by Doppler US and MR imaging.

A prospective study compared the efficacy of Doppler ultrasonography (US) and magnetic resonance (MR) imaging in evaluating 38 renal allografts, with specific attention to transplant rejection. Forty-three Doppler US and 42 MR examinations were performed and interpreted. Histologic correlation was obtained from 22 biopsy or nephrectomy specimens. Clinical correlation or a response to instituted therapy was used as confirmation in the remaining allografts. Accuracy in identifying cyclosporine toxicity or acute tubular necrosis could not be evaluated because there were few such cases, with concomitant rejection in most. The ability to predict and identify presence or absence of rejection was not affected by different serum creatinine values. Doppler US was significantly superior to MR imaging in identifying allograft rejection, demonstrating a higher sensitivity (95% vs. 70%), specificity (95% vs. 73%), and accuracy (95% vs. 71%). Because of its low cost and accessibility, Doppler US should become the primary modality for renal transplant screening.

Adult↗