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Biomedical subjects

E V Garcia

Publications and source records attributed to E V Garcia.

At least 19 recordsLinked to original sources
PubMed1992

SPECT quantification: a simplified method of attenuation and scatter correction for cardiac imaging.

The quantitative and visual interpretation of SPECT myocardial perfusion images is limited by physical factors such as photon attenuation, Compton scatter, and finite resolution effects. A method of attenuation correction is described for use in nonhomogeneous media and applied to cardiac SPECT imaging. This method, termed multiplicative variable attenuation compensation (MVAC), uses tissue contours determined from segmentation of a transmission scan to assign a priori determined attenuation coefficients to different tissue regions of the transaxial images. An attenuation correction map is then constructed using a technique inspired by Chang's method that includes regionally dependent attenuation within the chest cavity and is applied after reconstruction by filtered backprojection. Scatter correction using the subtraction of a simultaneously acquired scatter window image enables the use of narrow beam attenuation coefficients. Experimental measurements to evaluate these methods were conducted for 201Tl and 99mTc SPECT using a homomorphic cardiac phantom. Finite resolution effects were included in the evaluation of results by computer simulation of the three-dimensional activity distribution. The correction methodology was shown to substantially improve both relative and absolute quantification of uniform and nonuniform regions of activity in the phantom's myocardial wall.

Heart↗
PubMed1991

Evaluation of right ventricular regional perfusion with technetium-99m-sestamibi SPECT.

To evaluate technetium-99m-sestamibi as a right ventricular perfusion imaging agent, 25 normal volunteers and 25 patients with suspected coronary disease were studied with both sestamibi and thallium-201 SPECT. All patients underwent cardiac characterization. Compared to thallium-201 images, visualization of the right ventricle was superior for sestamibi in all cases. After computer masking of the left ventricle, count profiles for each 6-mm right ventricular short-axis slice were extracted and plotted in a bull's-eye type polar map with images normalized to maximal right ventricular counts. On sestamibi right ventricular polar maps, 7 of 11 patients (64%) with right coronary stenosis had fixed or reversible inferior right ventricular defects. None of the 25 volunteers or patients without right coronary stenosis had right ventricular defects (true-negative rate = 100%). We conclude that sestamibi SPECT provides an accurate means to assess right ventricular regional perfusion, with data presentation and interpretation facilitated by the polar map display.

Adult↗
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

Myocardial perfusion imaging with technetium-99m sestamibi SPECT in the evaluation of coronary artery disease.

Technetium-99m (Tc-99m) sestamibi is a new myocardial perfusion imaging agent that offers significant advantages over thallium-201 (Tl-201) for myocardial perfusion imaging. The results of the current clinical trials using acquisition and processing parameters similar to those for Tl-201 and a separate (2-day) injection protocol suggest that Tc-99m sestamibi and Tl-201 single photon emission computed tomography (SPECT) provide similar information with respect to detection of myocardial perfusion defects, assessment of the pattern of defect reversibility, overall detection of coronary artery disease (CAD) and detection of disease in individual coronary arteries. Tc-99m sestamibi SPECT appears to be superior to Tc-99m sestamibi planar imaging because the former provides a higher defect contrast and is more accurate for detection of disease in individual coronary arteries. Research is currently under way addressing optimization of acquisition and processing of Tc-99m sestamibi studies and development of quantitative algorithms for detection and localization of CAD and sizing of transmural and nontransmural myocardial perfusion defects. It is expected that with the implementation of the final results of these new developments, further significant improvement in image quality will be attained, which in turn will further increase the confidence in image interpretation. Development of algorithms for analysis of end-diastolic myocardial images may allow better evaluation of small and nontransmural myocardial defects. Furthermore, gated studies may provide valuable information with respect to regional myocardial wall motion and wall thickening. With the implementation of algorithms for attenuation and scatter correction, the overall specificity of Tc-99m sestamibi SPECT should improve significantly because of a substantial decrease in the occurrence of attenuation-related image artifacts.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗
PubMed1990

Comparison of SPECT using technetium-99m agents and thallium-201 and PET for the assessment of myocardial perfusion and viability.

This report reviews the applications of tomographic imaging with current and new tracers in assessing myocardial perfusion and viability. Multiple studies with thallium-201 (TI-201) single photon emission computed tomography (SPECT) imaging for the detection of coronary artery disease (CAD) have demonstrated high sensitivity, high rates of normalcy and high reproducibility. In assessing viability, fixed defects are frequently detected in viable zones in 4-hour studies with TI-201 imaging. Redistribution imaging performed 18 to 72 hours after injection or reinjection of TI-201 before 4-hour redistribution imaging has been shown to improve accuracy of viability assessment. TI-201 SPECT studies are limited by the suboptimal physical properties of TI-201, which result in variable image quality. The 2 new technetium-99m (Tc-99m) - labeled myocardial perfusion tracers offer the ability to inject much higher amounts of radioactivity, making it possible to assess ventricular function as well as myocardial perfusion from the same injection of radiotracer. Tc-99m sestamibi has very slow myocardial clearance, which allows for prolonged imaging time and results in image quality superior to that obtained with TI-201 and Tc-99m teboroxime. The combination of minimal redistribution of Tc-99m sestamibi and high count rates makes gated SPECT imaging feasible, and also permits assessment of patients with acute ischemic syndromes by uncoupling the time of injection from the time of imaging. The combination of high image quality and first-pass exercise capabilities may lead to a choice of this agent over TI-201 for assessment of chronic CAD.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary Disease↗
PubMed1990

Visualization of multimodality cardiac imagery.

A large number of clinically important and medically difficult decisions in diagnostic radiology involve interpreting the information derived from multiple imaging modalities. This is especially true in the assessment of heart disease, wherein at least two types of image information are generally required prior to deciding on the course of action: structural information describing coronary vessel anatomy and functional information related to heart muscle physiology. This paper will present and discuss the methods and results associated with a research program aimed at quantifying and visualizing the unified anatomic and physiologic information obtained from these complementary imaging modalities. The discussions will emphasize the reconstruction, processing, and visualization of three-dimensional cardiovascular structure, including the procedures and results obtained from phantom and patient studies.

Computer Graphics↗
PubMed1990

Quantification of the reversibility of stress-induced thallium-201 myocardial perfusion defects: a multicenter trial using bull's-eye polar maps and standard normal limits.

A multicenter trial was performed on 140 patients from four centers to determine the accuracy of quantitative analysis of stress/delayed thallium-201 myocardial tomograms using normal limits to assess the relative amount of reversibility of stress-induced defects. The patients were found to have 85 fixed and 124 reversible defects, as determined by visual interpretation. Reversibility bull's-eye polar maps were compared to gender-matched normal limits from 36 normals. Regions were identified as reversible if their normalized difference between stress and 4 hr greater than 1.5 s.d.s. from the mean normal limits. Overall agreement between experts at multicenter sites and reversibility maps was 73% for reversible defects and 80% of fixed defects. Sensitivity in detecting reversibility was highest for the left circumflex (88%) and lowest for the right coronary (60%). These results indicate that reversibility polar maps and normal limits offer an objective, accurate technique for determining the reversibility of stress-induced perfusion defects.

Adult↗
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↗
PubMed1989

Sequential multivessel coronary angioplasty assessed by thallium-201 tomography.

In 11 patients with multivessel coronary artery disease, SPECT thallium-201 imaging was performed prior to and within 3 days after each of two sequential percutaneous transluminal coronary angioplasties on separate days designed to achieve total revascularization. Thallium-201 SPECT was analyzed quantitatively, and an ischemic score for the vascular bed(s) supplied by the dilated vessel(s) was derived. For the vessels dilated during the first procedure the mean diameter stenosis was 80 +/- 8%, reduced to 27 +/- 9%. For the second procedure mean stenosis was reduced from 67 +/- 10% to 26 +/- 6%. For the two procedures, the mean thallium scores decreased from 298 +/- 225 to 115 +/- 130 (P less than .001) and from 135 +/- 129 to 46 +/- 60 (P less than .001), respectively. Of 10 patients with abnormal thallium-201 SPECT prior to angioplasty, nine improved after the first procedure, and seven improved further following the second procedure. Thus, utilizing staged angioplasty with a strategy of dilating the most severe lesion first, thallium-201 SPECT documented progressive improvement in myocardial perfusion.

Angioplasty, Balloon, Coronary↗
PubMed1989

Quantitative single photon emission computed thallium-201 tomography for detection and localization of coronary artery disease: optimization and prospective validation of a new technique.

One hundred eight-three men underwent stress-redistribution thallium-201 myocardial perfusion tomography. After evaluation of various preprocessing filters in a phantom study, the Butterworth filter with a frequency cutoff of 0.2 cycles/pixel, order 5 (which provided optimal filter power) was used in the back projection algorithm of the patient studies. All short-axis and apical portions of vertical long-axis images were quantified by dividing each myocardial slice into 60 equal sectors and displaying the maximal count per sector as a linear profile. In a pilot group consisting of 20 normal men (less than 5% likelihood of coronary artery disease) and 25 men with coronary artery disease (greater than or equal to 50% coronary stenosis by angiography), profiles representing the lowest observed value below the mean normal profiles provided the best threshold for defining normal limits. Abnormal portions of the patient profiles were plotted on a two-dimensional polar map. The polar map was divided into 102 sectors, and sectors with a probability of greater than or equal to 80% for disease of each one of the three major coronary arteries were clustered to represent specific coronary artery territories. Receiver operating characteristic curve analysis for defect size showed that the optimal threshold for defining a definite perfusion defect was 12% for the left anterior descending and left circumflex and 8% for the right coronary artery territories. These criteria were prospectively applied to an additional 92 patients with angiographic coronary artery disease, 18 patients with normal coronary arteriograms and 28 patients with less than 5% likelihood of coronary disease. Sensitivity, specificity (in patients with normal coronary arteriograms) and normalcy rate (in patients with less than 5% likelihood of coronary artery disease) for overall detection of coronary disease were 96%, 56% and 86%, respectively. Sensitivity and specificity for identification of individual diseased vessels were, respectively, 78% and 85% for the left anterior descending, 79% and 60% for the left circumflex and 81% and 71% for the right coronary artery. These results were not significantly different from those of the pilot group. An optimized quantitative method for interpretation of stress thallium-201 myocardial perfusion tomography has been developed. Prospective application of this method indicates that the technique is accurate for the overall detection of coronary artery disease and identification of disease in individual arteries.

Coronary Circulation↗
PubMed1989

Three-dimensional techniques and artificial intelligence in thallium-201 cardiac imaging.

Three-dimensional reconstruction techniques including bull's-eye polar-coordinate maps, surface rendering, and surface modeling have been developed that help interpreting physicians assimilate complex 3-D tomographic data. Comparison of patient data with normal files highlights myocardial perfusion abnormalities, thus facilitating their recognition. In addition, AI systems that use heuristically defined rules derived from an expert knowledge base assist inexperienced observers in drawing conclusions regarding scan abnormalities.

Artificial Intelligence↗
PubMed1989

Optimal specificity of thallium-201 SPECT through recognition of imaging artifacts.

Artifacts are produced in 201TI cardiac single photon emission computed tomography (SPECT) imaging because of a variety of causes including soft-tissue attenuation, overlying abdominal viscera, variable myocardial thickness, left bundle branch block, cardiac rotation, patient motion, and technical errors. Careful attention to quality control, utilization of motion detectors, and familiarization with potential artifacts will improve the specificity and diagnostic accuracy of 201TI SPECT for coronary artery disease.

Abdomen↗
PubMed1988

Incomplete redistribution in delayed thallium-201 single photon emission computed tomographic (SPECT) images: an overestimation of myocardial scarring.

To determine if incomplete redistribution at 4 h in exercise tomographic thallium-201 studies is always due to a myocardial scar, 141 patients were evaluated before and after a total of 160 successful percutaneous transluminal coronary angioplasty procedures. Thallium studies were analyzed using polar "bull's-eye" maps. For both immediate and delayed images, abnormalities were quantified as a thallium score by calculating a standard deviation-weighted sum of pixels greater than 2.5 SD below gender-matched normal limits. One hundred forty-four of 160 studies indicated abnormalities before angioplasty. Of these 144, incomplete redistribution occurred in 111 (77%): 16 (14%) in patients with and 95 (86%) in patients without prior Q wave myocardial infarction. After angioplasty, improvement in delayed image score occurred in 8 (50%) of 16 patients with prior infarction and 72 (76%) of 95 patients without prior infarction (p less than 0.05). After angioplasty, delayed images were normal in 1 (6%) of 16 patients with prior infarction and 32 (34%) of the 95 without (p less than 0.05). Before angioplasty, delayed image scores were positively correlated with scores in the immediate postexercise images in patients with (r = 0.84) and those without (r = 0.69) prior infarction. To determine if additional delayed images could help differentiate scar from ischemia, an 8 to 24 h delayed image was obtained in each of 40 other patients with incomplete redistribution at 4 h. Of 28 patients without prior infarction, 15 had no redistribution, and 13 had further redistribution at 8 to 24 h.

Adult↗
PubMed1988

Patient motion in thallium-201 myocardial SPECT imaging. An easily identified frequent source of artifactual defect.

Because Tl-201 SPECT requires that patients remain in an awkward position for a prolonged time, patient motion is a potentially serious source of artifactual defects on tomographic reconstructions. Thus, a simple method was developed for detection and correction of motion from SPECT images using a Co-57 point source placed on the lower anterior chest, an area remaining in the camera's field of view throughout imaging. In the absence of motion, this point source inscribes a straight line on planar summation of the 32 projections over 180 degrees. Movement is detected by deviation from this line. The number of pixels of motion is used to shift images so that the resultant images of the point source are linear. The method of motion detection and correction was tested in 48 consecutive patients undergoing Tl-201 SPECT. The corrected and uncorrected images were reconstructed and long and short axis tomographic cuts were quantitatively analyzed using circumferential profiles of maximal counts with comparison to the lower limits of normal. Motion was detected in eight of 48 patients (17%). The amount of motion was 2 pixels in three patients and 1 pixel in five patients. Quantitative defect extent was less after correction in seven of eight patients, with a mean decrease of 71% in patients with 2 pixel motion and 44% in patients with 1 pixel motion. This corresponded with a definite reduction in the size of the tomographic defect by visual analysis, and closer resemblance to quantitatively analyzed planar images performed either before or after tomography in the same patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Quantitative rotational thallium-201 tomography for identifying and localizing coronary artery disease.

The purpose of this study was to develop and validate a method for quantifying the uptake, redistribution, and washout of thallium-201 (201Tl) obtained with rotational tomography. This method generates maximum count circumferential profiles of the short-axis slices of the left ventricle, translates them into polar coordinate profiles, and displays them as a bullseye plot, which consists of a series of concentric circles with the apex at the center and the base at the periphery. Normal limits were established for the distribution of 201Tl in 36 patients with a low (less than 5%) probability of coronary artery disease (CAD). Forty-five patients who had undergone coronary angiography were used as a pilot group to define criteria for the identification and localization of perfusion defects. The best agreement with the results of angiography was found when abnormal regions of the bullseye were defined as contiguous defects over 2.5 SDs below normal. These criteria were applied prospectively to 210 points (179 points with greater than 50% diameter stenosis and 31 with less than 50%). Visual, quantitative, and combined visual and quantitative analysis were compared for overall detection of disease and for detection of individual vessel involvement. The overall sensitivity for detection of disease by these methods was 97%, 95%, and 95%, respectively. The specificities were 68%, 74%, and 71% respectively. The sensitivity for detection of individual vessel involvement with the bullseye alone was 78% for the left anterior descending artery (LAD), 89% for the right coronary artery (RCA), and 65% for the left circumflex (LCx). For visual analysis, the results were 70%, 88%, and 50%, respectively, while the use of visual and quantitative analysis combined identified 75% of LAD, 87% of RCA, and 55% of LCx lesions. We conclude that quantitative analysis of rotational 201Tl tomographic images is a highly accurate technique for determining the presence and location of CAD.

Adult↗
PubMed1987

Quantitative planar and tomographic thallium-201 myocardial perfusion imaging.

Quantification of thallium myocardial studies affords the advantage of objectivity over visual analysis. Moreover, comparison of patient profiles to normal limits gives nonexpert readers a sense of confidence for interpreting these studies. Quantification of the washout rate from planar scintigrams aids in overcoming any lack of contrast. Tomography has excellent contrast resolution and identifies most stress perfusion defects without the need for washout calculations. Moreover, with the use of polar displays such as the Bullseye map, the perfusion defect is better characterized by tomography in terms of its location, shape, and size. The main caveat in the use of tomography is that it is technically demanding. The decision as to which method to use depends largely on the application and on the instrumentation and technical expertise available.

Coronary Disease↗