Biomedical subjects

R Folks

Publications and source records attributed to R Folks.

7 recordsLinked to original sources

PubMed1995

Measuring technetium-99m-MAG3 clearance with an improved camera-based method.

UNLABELLED: Because commercially available camera-based methods are not optimized, they fail to account for dose infiltration, table attenuation and correspondence between time of injection and starting the camera. We have developed a more optimized technique to calculate camera-based clearances and applied this technique in the design of a camera-based clearance method for 99mTc-MAG3. METHODS: Technetium-99m-MAG3 scintigraphy was performed in 20 patients who had varying degrees of renal function. Data were acquired posteriorly in supine patients at 2 sec/frame for 24 frames, 15 sec/frame for 16 frames and 30 sec/frame for 40 frames. Background correction was performed using an automated elliptical region of interest. Renal depth was estimated using improved regression equations and an empirically determined attenuation coefficient derived from phantom studies. Corrections were made for table attenuation and time discrepancies between dose injection and starting the camera. The percent injected dose in the kidney at 1-2, 1-2.5 and 2-3 min postinjection and the percent injected dose at those time periods corrected for body surface area were correlated with MAG3 clearance based on a single injection, two-compartment model. RESULTS: There was high correlation between the percent injected dose in the kidney at all three time periods and the multisample clearance. Correcting for body surface areas significantly improved the correlation coefficients. Consequently, regression equations were developed to predict multisample clearance based on percent dose and body surface area. CONCLUSION: The optimization features described in this method should improve precision when sequential studies are conducted in the same patient.

Adult↗

PubMed1994

Evaluation of technetium-99m-triamide-mercaptide complexes designed to identify properties favoring renal tubular transport.

UNLABELLED: To aid in the design of an improved 99mTc-labeled renal agent, several new [99mTcO(MAG3)]2- analogs were synthesized to determine the effects of varying the position and chemical form of the terminal charged group on renal clearance. METHODS: Clearance, extraction efficiency and plasma protein binding were measured in six Sprague-Dawley rats per complex for ortho, meta and para isomers of [99mTcO(MAG2-ABA)]2-, with MAG2- = mercaptoacetylglycylglycyl- and ABA = aminobenzoate; [99mTcO(MAG2-pASA)]2-, with pASA = p-aminosalicylate; [99mTcO(MAG2-AMS]2-, with AMS = aminomethylsulfonate; and [99mTcO(MAG2-AMP]3-, with AMP = aminomethylphosphonate. For agents with relatively poor clearances, hepatobiliary excretion was evaluated by using a camera-based method. RESULTS: The clearances of the ortho, meta and para isomers of [99mTcO(MAG2-ABA)]2- were 17%, 20% and 59% of those of OIH, respectively. The clearances of [99mTcO(MAG2-pASA)]2-, [99mTcO(MAG2-AMS)]2- and [99mTcO(MAG2-AMP)]3- were 32%, 46% and 39% those of OIH, respectively. CONCLUSION: Optimal tubular transport appears to require a terminal anionic group; a planar carboxylate is preferred over nonplanar -SO3- or -PO3(2-) substituents, suggesting that the smaller size and/or planar shape of the carboxylate group are probably more important than the total charge or charge distribution. Optimal transport also appears to depend on the oxo-carboxylate conformation (syn or anti) and the oxo-carboxylate distance, although these relationships can be modulated by steric interactions. These structure-distribution relationships are important factors to consider in the future design of renal radiopharmaceuticals.

Animals↗

PubMed1994

Multicenter trial validation for quantitative analysis of same-day rest-stress technetium-99m-sestamibi myocardial tomograms.

UNLABELLED: The accuracy of an automated quantitative analysis of same-day rest/stress 99mTc sestamibi SPECT images for detection and localization of coronary artery disease (CAD) was assessed in a multicenter trial consisting of 161 patients from 7 different clinical sites utilizing various camera computer systems. METHODS: Of the 161 patients, 102 had angiographically documented coronary artery disease, 22 had normal coronary arteriograms, and 37 had a low (< 5%) likelihood of coronary artery disease based on their age, sex, symptoms and the results of their exercise electrocardiograms. The patients were studied using previously optimized image acquisition and processing protocols. An additional population consisting of 45 patients with single-vessel disease were evaluated to determine the optimal criteria for detection of CAD. RESULTS: The quantitative analysis method was associated with an overall sensitivity of 87%, specificity of 36%, and normalcy rate (true negative rate in the low likelihood patients) of 81%. Sensitivity for overall detection of disease was similar (90%) in patients with and without myocardial infarction (90% versus 89%). The sensitivities and specificities for identification of disease in individual coronary arteries were, respectively, 69% and 76% for LAD, 70% and 80% for LCX, and 77% and 85% for RCA. CONCLUSION: The results of this study demonstrate that the new objective quantitative method for analysis of same-day rest/stress 99mTc sestamibi SPECT images is accurate for detection and localization of CAD and correlates highly with expert visual interpretation.

Adolescent↗

PubMed1993

Quantitative same-day rest-stress technetium-99m-sestamibi SPECT: definition and validation of stress normal limits and criteria for abnormality.

Gender-matched stress normal limits and criteria for abnormality for rest-stress 99mTc-sestamibi same-day myocardial perfusion imaging were developed and validated in 160 patients who were imaged using previously developed optimized acquisition, processing and quantitative protocols. The gender-matched mean and standard deviation of the normal response were calculated using 35 male and 25 female patients with a < 5% likelihood of coronary artery disease. Receiver-operating curve analysis using expert visual interpretation as the "gold standard" was used to determine the optimal criteria for abnormality detection, in terms of standard deviations from the mean and minimum defect size for each of the four major zones of the polar map, in a pilot population consisting of an additional 35 male and 25 female patients with a variety of perfusion defects. The optimum standard deviations resulted in the following true-positive/true-negative rates when quantitative results were compared to visual analysis for the anterior, septal, lateral, and inferior segments in the combined male and female pilot populations: 84%/86%, 70%/75%, 86%/76% and 69%/76%, respectively. The final criteria were then applied to a prospective population consisting of 33 male and 7 female patients. This analysis resulted in the following true-positive/true-negative rates for overall perfusion abnormalities and abnormalities of the LAD, LCX and RCA vascular territories: 97%/67%, 94%/73%, 73%/90% and 72%/91%, respectively. The optimized 99mTc-sestamibi stress normal limits and criteria for abnormality correlate well with expert visual interpretation of stress myocardial perfusion defects.

Coronary Disease↗

PubMed1992

Prospective validation of a single sample technique to determine technetium-99m-MAG3 clearance.

Technetium-99m-MAG3 clearance is proportional to OIH clearance and can be used directly as a measure of renal function. Multiple plasma sample, two-compartment clearance data from three studies were recently pooled to develop a single-sample regression equation for determining the clearance of 99mTc-MAG3. To test this published equation, a prospective study was conducted in 34 patients with a wide range of renal function. Multiple plasma samples were obtained from 9 to 60 min following the bolus injection of 99mTc-MAG3 and the clearances were calculated based on a single injection, two-compartment model. Clearances were also calculated using a single 43-min plasma sample and the published regression equation. There was an excellent correlation (r = 0.976) between the two clearances; the slope of the regression line was 1.01 with an intercept of -26.6; the standard error of the estimate was 24 ml/min. In conclusion, the current regression equation provides a good estimate of 99mTc-MAG3 clearance.

Chromatography, High Pressure Liquid↗

PubMed1990

Technical aspects of myocardial SPECT imaging with technetium-99m sestamibi.

Most reports to date using single photon emission computed tomography (SPECT) with technetium-99m (Tc-99m) sestamibi have used acquisition parameters that were optimized for thallium-201. To fully utilize the superior imaging characteristics of Tc-99m sestamibi, there is a need to optimize the technical aspects of SPECT imaging for this agent. Performance can be enhanced through the careful selection of optimal radiopharmaceutical doses, imaging sequences, acquisition parameters, reconstruction filters, perfusion quantification methods and multidimensional methods for visualizing perfusion distribution. The current report describes theoretical considerations, phantom studies and preliminary patient results that have led to optimized protocols, developed at Emory University and Cedars-Sinai Medical Center, for same-day rest-stress studies, given existing instrumentation and recommended dose limits. The optimizations were designed to fit a low-dose-high-dose rest-stress same-day imaging protocol. A principal change in the acquisition parameters compared with previous Tc-99m sestamibi protocols is the use of a high-resolution collimator. The approach is being developed in both prone and supine positions. A new method for extracting a 3-dimensional myocardial count distribution has been developed that uses spherical coordinates to sample the apical region and cylindrical coordinates to sample the rest of the myocardium. New methods for visualizing the myocardial distribution in multiple dimensions are also described, with improved 2-dimensional, as well as 3- and 4-dimensional (3 dimensions plus time) displays. In the improved 2-dimensional display, distance-weighted and volume-weighted polar maps are used that appear to significantly improve the representation of defect location and defect extent, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Graphics↗

PubMed1990

Reversibility bull's-eye: a new polar bull's-eye map to quantify reversibility of stress-induced SPECT thallium-201 myocardial perfusion defects.

Myocardial ischemia is currently interpreted from SPECT thallium-201 (201Tl) tomograms by the subjective visual finding of stress-induced perfusion defects which "normalize" or "reverse" by 4 hr. Thus, we have developed a computer method to quantify and display the three-dimensional distribution of reversible segments. Circumferential profiles generated from the short axis slices are normalized to the reference area in the stress study. The stress is subtracted from the normalized delayed data, and then displayed as a polar bull's-eye plot so that positive values show areas that have "reversed" or "improved." Patient profiles are compared to means and standard deviations of reversibility for all pixels determined from the Emory normal male files. Criteria for reversibility were developed from studies of 42 male patients found to have 48 defects, as determined by the consensus of five blinded expert observers. There was computer agreement with the experts on 25 of 31 relatively fixed and 14 of 17 reversible defects. Our preliminary results indicate that this new method promises to aid observers to more consistently identify and quantify the reversibility of SPECT 201Tl myocardial perfusion defects.

Adult↗