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Biomedical subjects

J W Fletcher

Publications and source records attributed to J W Fletcher.

At least 19 recordsLinked to original sources
PubMed1990

Observer reliability in CT and MRI of the abdomen/pelvis.

The purpose of this research was to evaluate two sources of error in the performance of computerized tomography (CT) and magnetic resonance imaging (MRI) of the abdomen/pelvis. The sources of error assessed were inter- and intra-observer reliability. Thirty abdomen/pelvis CT scans were randomly selected from each of three hospitals (university, VA, military) with different CT scanners. Two radiologists were recruited from each site to be CT observers. Forty-five abdomen/pelvis MRI scans were randomly selected from two institutions with different MRI scanners. Four observers were recruited to read the MRI scans. All scans were read blind without clinical information or patient identification. Overall inter-observer and intra-observer diagnostic agreement was significantly higher for MRI compared to CT. Inter-observer diagnostic agreement rates were also significantly higher for MRI when the etiologies of neoplastic vascular and metabolic/toxic were assigned. Observer experience in CT (range: 5-9 yr) or MRI (range: 2-4 yr) was not statistically associated with improved diagnostic agreement. This research addresses many of the criticisms of the MRI literature and compares MRI favorably to CT.

Abdomen↗
PubMed1989

Practice pattern variation between two medical schools.

This study examined physician test-ordering behavior at a large urban Veterans Administration Medical Center staffed by two medical schools. Patients are assigned randomly to the two schools' wards, which operate independently of each other. The medical records of 119 patients, admitted during a 5-month period, were abstracted for data on the process and outcomes of medical care. Only one statistically significant difference in diagnostic testing practices was revealed by the observation that 12% of patients on one service received another abdominal film, while no patients on the other service did. The implications of studies such as this for small-area analysis are discussed. If variation in the utilization of health services is observed in a geographic region, then a study of physician behavior at a single facility may help to identify the reason for the variation.

Diagnosis-Related Groups↗
PubMed1987

High signal intensity soft tissue masses on T1 weighted pulsing sequences.

On T1 weighted pulsing sequences, the majority of soft tissue masses are of low signal intensity and show high intensity signals on T2 weighting. There however is a subset of soft tissue masses of varied histology that shows high signal intensity on T1 weighted pulsing sequences. These masses have either fat or blood in their substance. Lipomatous and hemangiomatous lesions that did not show high-signal intensity on T1 weighting were also encountered and are discussed. Present experience with MRI of soft tissue masses suggests that there is a limited spectrum of entities that produce high-signal intensity T1 weighted soft tissue masses.

Cysts↗
PubMed1987

Atrial pacing and thallium 201 scintigraphy: combined use for diagnosis of coronary artery disease.

To evaluate the presence of coronary artery disease (CAD), atrial pacing and thallium 201 scintigraphy were performed in 36 patients with stable angina pectoris who were unable to perform an adequate exercise stress test. All patients underwent cardiac catheterization. Nine patients had previously undergone coronary artery bypass surgery. Significant CAD (one or more lesions greater than or equal to 50%) was present in 33 patients. Atrial pacing produced ischemic ST segment depression (greater than or equal to 1 mm) in 18 (55%) patients with CAD, and angina in 20 patients (61%). As the number of vessels with CAD increased, there was no significant change in the sensitivities of pacing-induced angina or ST segment depression for detecting CAD. In the 3 patients without CAD, ST segment depression occurred in 1 patient and angina in none. Thallium 201 scintigraphy demonstrated perfusion defects in 27 (82%) patients with CAD, with fixed defects seen in 13 studies (39%) and reversible defects in 15 (45%). In the 3 patients without CAD, no perfusion defects were seen. The thallium 201 scan successfully predicted the presence of CAD in patients with single-vessel disease but usually underestimated the number of vessels involved in patients with multivessel disease. Combined sensitivity of pacing-induced ST segment depression and an abnormal thallium 201 scan finding for detecting CAD was 91%. The authors conclude that combined atrial pacing and thallium 201 scintigraphy is a useful test for detecting CAD in patients unable to perform an adequate exercise stress test.

Aged↗
PubMed1987

Coronary artery bypass grafting in a predominately black group of patients.

The preoperative profiles of a predominately non-white group of patients undergoing coronary artery bypass grafting were reviewed. Data were obtained from a retrospective analysis of medical records of 163 patients operated on at Howard University Hospital between July 1983 and July 1986. The analysis was carried out primarily to determine whether patients requiring myocardial revascularization were somehow different from their non-black counterparts. Ninety-one percent of the patients were black, 5 percent white, 0.5 percent Hispanic, and 3.5 percent others (Iranian, Filipino, etc).The study was not designed to review the prevalence of coronary disease in blacks, or to determine the natural history following coronary artery bypass grafting, but to determine whether those with established coronary disease of such a severity as to warrant revascularization had the usual clustering of risk factors. Patient records were reviewed to determine the prevalence of hypertension, diabetes, obesity, cigarette smoking, previous myocardial injury, and total serum cholesterol. Because of the well-recognized increased incidence of hypertension in black patients, and its role as a major risk factor in coronary heart disease, the sequelae of hypertension were considered in relation to results of surgical therapy.The study population included 93 men (57 percent) and 70 women (43 percent); mean age was 59 years (fourth to ninth decade). Seventy-four percent of the patients were hypertensive, 35 percent were diabetic, and 77 percent had a smoking history. Obesity was prevalent among the female patients in general, with 36 percent of the diabetics and 21 percent of the nondiabetics being greater than 50 percent over ideal body weight. Ninety percent of the female patients and 80 percent of the male patients presented with New York Heart Association class III or IV angina. Left ventricular function was, on the average, well preserved. The immediate surgical mortality (following exclusion of patients in extremis) was 4 percent. The surgical mortalities were related to easily identifiable factors. Peri-operative infarctions were profoundly influenced by the presence of diabetes.Although this group was distinguished from most reported groups of patients undergoing aortocoronary bypass grafting by the presence of advanced age, the large percentage of women and diabetics and the marked prevalence of hypertension, and the usual risk factors for coronary artery disease reported in the majority population, the study reconfirms previous epidemiologic findings. It appears that racial "clumping" of a heterogeneous non-white population has minimal usefulness, except as it may be related to socioeconomic status and access to quality health care.

Adult↗
PubMed1986

Two-point T1 measurement: wide-coverage optimizations by stochastic simulations.

Stochastic reliability of T1 measurement from image signal ratios is examined in the ideal case by stochastic simulations in the context of wide-coverage optimizations. Precise measurements prove to be accurate, and accurate ones precise. Sign-preserved inversion-recovery (IR)/non-IR techniques are the best ratio method, reciprocal non-IR/IR ones being equivalent, but inconvenient. Wide-coverage optima are relatively unsharp. Suggested guidelines for covering the 150- to 1500-ms T1 band are minimal relevant TE; TI about 400 ms; effective repetition times about in the ratio, TR2(IR)/TR1 (non-IR) = 2.5-3.0, and in a sum as long as possible up to about TR1 + TR2 = 3.5-4.0 s; signal-averaging after and only after TR1 + TR2 has been lengthened to the said region. Also suggested are different guidelines for covering T1 bands, 120-1200 and 200-1800 ms. Typically, precisions and accuracies improve linearly or faster with increasing S/N and (S/N)2, respectively. Unnecessarily high pixel resolutions or thin slicings exact great penalties in accuracies. Progressively shortening TR1 eventually transforms a wide coverage into a sharp targeting with small potential gains in a narrow T1 locality and large compromises almost everywhere else. The simulations yield an insight into applicabilities of standard error propagation analyses in two-point T1 measurement.

Biometry↗
PubMed1986

Significance of diffuse cardiac activity on In-111 labeled leucocyte scans.

To assess the significance of diffuse cardiac activity (DCA) seen on In-111 labeled leukocyte scans, we reviewed 87 studies performed over the last 4 years. Inflammatory cardiac conditions were seen as frequently in patients with DCA (15%) as those without (7%, P = 0.3). There was a higher ratio of RBC:WBC in the final WBC preparation in the false-positive DCA group than the true positive DCA and no DCA groups. False-positive studies showing DCA are most likely due to residual blood pool activity.

Adolescent↗
PubMed1986

Numerical T1 computation from NMR intensity ratios.

Two-point measurement of tissue T1 from NMR intensity ratios consists of forming an a priori ratio function describing a T1 dependence of the ratio R(T1) and computing T1 from an observed ratio Q by numerically solving R(T1)-Q = 0 or an equivalent equation. Impact of R(T1) designs on the numerical computation and dependence of relative speeds of three numerical methods on desired computational precisions q and on other factors are examined. All three methods begin with computing a table of R(T1) entries in uniform T1 steps (delta T1). In two iterative methods, a step containing the T1 root is looked up, and the precise T1 location within the step is pinpointed to within a q value by either linear-interpolative (LI) or Newton-Raphson (NR) iteration. The third method simply consists of computing a large table of delta T1 = q for a mere "look-up" with no iterative search. All three methods require a monotonous R(T1) for uniformly effective computation over wide T1 ranges. Speeds of either iterative method for computing T1 images are expected to vary with delta T1 and q with unsharp speed maxima at delta T1 near 20, 6, and 2 ms for q = 10(-1), 10(-2), and 10(-3) ms, respectively. Either iterative method is suitable for both low- and high-precision computations, the LI method being generally faster. The simple look-up is the fastest of the three for T1 image computation to low precisions of q greater than or equal to 1 ms, is likely the slowest for that to q = 0.1 ms, and is impractical for that to q less than or equal to 0.01 ms.

Algorithms↗
PubMed1986

Prospective pricing system for tertiary neonatal intensive care.

This study assessed the potential impact of the federal neonatal diagnosis-related group (DRG) pricing system upon reimbursement to a state neonatal intensive care program. Data for length of intensive care unit stay, procedures, hospital charges, and audited cost reports from the state of Florida's ten regional neonatal intensive care centers were analyzed for 8,492 neonates whose charges totaled $118 million. Mean lengths of stay in these tertiary care centers were substantially longer than those reported for the federal DRGs, which were based on community hospital data. If federal DRG-based reimbursement to hospitals were implemented in Florida's perinatal intensive care program, compensation would range from 9% to 56% of actual hospital care charges. Federal DRG price rates were not predictive of hospital charges. Only 16% of the total variation in hospital charges was explained by differences among federal DRG rates (R2 = .16). Analysis of data by major determinants of resource consumption provided groups more homogeneous with respect to hospital charges and, hence, cost. Therefore, we developed a prospective pricing system that used modifications of federal newborn DRG system. These modifications resulted in a threefold increase in R2 (.52). Our proposed system permits prediction of cost and reimbursement for infants by three criteria: birth weight, need for mechanical ventilation and/or major surgery, and survival status and length of survival for those who die.

Analysis of Variance↗
PubMed1979

Radionuclide venography and lung scanning: Concise communication.

In 102 patients suspected of pulmonary embolism, we have assessed the ability of a radionuclide (emission) venogram to complement the pulmonary perfusion scintigram in establishing a diagnosis. The efficacy was compared using decision analysis and Bayes's theorem. Two criteria for a positive test were compared: Criterion 1--the test is positive if the lung scan a) indicates a high probability of pulmonary embolus, or b) is abnormal but indeterminate for pulmonary embolus; Criterion 2--the test is positive a) if the lung scan indicates a high probability of pulmonary embolus, or b) if the emission venogram is positive in a patient with a lung scan considered abnormal but indeterminate for pulmonary embolus. The use of Criterion 2 decreased the sensitivity from 100% to 95% and increased the specificity from 74% to 93%. We conclude that a simultaneous emission venogram assists in improving the specificity, accuracy, and the predictive value of a standard pulmonary perfusion study in the diagnosis of pulmonary embolus.

Foot↗
PubMed1978

Diagnosis of coronary artery disease with 201Tl. Computer analysis of myocardial perfusion images.

The diagnostic sensitivity of visually interpreted and computer-analyzed 201Tl myocardial perfusion images was compared to that of exercise electrocardiograms in 8 angiographically normal subjects and 24 patients with significant coronary artery disease. Visual interpretation was not significantly better than exercise ECGs. An index of perfusion homogeneity, derived from computer analysis of the 201Tl images, was more sensitive than visual interpretation (79% vs. 58%) and much more sensitive (p less than 0.05) than the exercise ECG (79% VS. 46%). The best overall sensitivity (88%) and specificity (75%) were achieved by combining computer analysis with exercise electrocardiography. The computer also permits enhanced detection of subtle perfusion changes which may not seem significant to the eye.

Computers↗
PubMed1975

Brain scans, dexamethasone therapy, and brain tumors.

Eight men with primary or metastatic brain tumors were examined with brain scans before and after the administration of dexamethasone. All patients demonstrated some improvement in their clinical neurologic status during therapy, and two patients had a dramatic response. Seven of the eight patients examined showed a decrease in the apparent size of the original lesion on recent brain scan while receiving dexamethasone. Comparison of immediate scans obtained 15 to 20 minutes following the administration of sodium pertechnetate Tc 99m with those obtained two or three hours later suggests that the change in apparent size of the original lesion results from decrease in peritumor edema.

Adult↗
PubMed1975

67Ga citrate distribution following whole-body irradiation or chemotherapy.

Whole-body retention, organ distribution, excretion, and serum binding of 67Ga were evaluated in rats under normal conditions and following whole-body gamma irradiation, vincristine sulfate, or mechlorethamine. The results suggest that both irradiation and chemotherapy lead to reduced whole-body retention of injected radiogallium, explained in part by an alteration in the serum binding of gallium. Recognition of these findings should be considered in interpreting decreased tumor concentration of gallium in patients following radiotherapy or chemotherapy.

Animals↗
PubMed1975

Liver scanning and the intrahepatic gallbladder: Case report.

Hepatic focal defects identified with 99mTc-sulfur colloid imaging procedures are nonspecific. This report describes a case of an ectopic gallbladder localized by cholecystography and 131I-rose bengal studies in a patient with cirrhosis and suspected intrahepatic neoplasm.

Colloids↗
PubMed1975

Radioisotopic detection of osseius metastases. Evaluation of 99mTc polyphosphate and 99mTc pyrophosphate.

A total of 146 patients were investigated for the presence of osseous metastases with 99mTc polyphosphate or 99mTc pyrophosphate bone scans. Results of bone imaging were retrospectively compared to roentgenographic results surveying similar anatomic areas in 128 patients. This comparison revealed that roentgenographic interpretations were in error in 19% of the cases. Thirty-three patients had bone scans and roentgenograms that were in agreement and considered abnormal, but in more than one third of these cases the patients had multiple abnormalities that were shown by the bone scan but were not recognized roentgenographically. In consideration of the low toxicity, ready availability, economy, shortened procedure time, and low radiation dose associated with the use of these new bone-seeking agents, it is concluded that they are superior to roentgenograms and previously utilized radionuclides for early detection of osseous metastases.

Bone Neoplasms↗