Joseph Areeda

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)

Comparative prognostic value of automatic quantitative analysis versus semiquantitative visual analysis of exercise myocardial perfusion single-photon emission computed tomography☆

OBJECTIVES The purpose of this study was to determine the prognostic value of automatic quantitative analysis in exercise dual-isotope myocardial perfusion single-photon emission computed tomography (SPECT) and to compare the prognostic value of quantitative analysis to semiquantitative visual SPECT analysis. BACKGROUND Extent, severity and reversibility of exercise myocardial perfusion defects have been shown to correlate with prognosis. However, most studies examining the prognostic value of SPECT in chronic coronary artery disease (CAD) have been based on visual analysis by experts. METHODS We studied 1,043 consecutive patients with known or suspected CAD who underwent rest Tl-201/exercise Tc-99m sestamibi dual-isotope myocardial perfusion SPECT and were followed up for at least 1 year (mean 20.0+/-3.7 months). After censoring 59 patients with early coronary artery bypass grafting or percutaneous transluminal coronary angioplasty, <60 days after nuclear testing, the final population consisted of 984 patients (36% women, mean age 63+/-12 years). RESULTS During the follow-up period, 28 hard events (14 cardiac deaths, 14 nonfatal myocardial infarctions) occurred. Patients with higher defect extent (>10%), severity (>150) and reversibility (>5%) by quantitative SPECT defect analysis, as well as those with an abnormal scan (>2 abnormal segments, summed stress score >4 and summed difference score >2) by semiquantitative visual SPECT analysis, had a significantly higher hard event rate compared to patients with a normal scan (p < 0.001). With both visual and quantitative analyses, hard event rates of approximately 1% with normal scans and 5% with abnormal scans (p > 0.05) were observed over the 20-month follow-up period. A Cox proportional hazards regression model showed that chi-square increased similarly with the addition of quantitative defect extent and visual summed stress score variables after considering both clinical and exercise variables (improvement chi-square = 11 for both, p < 0.0007). There were no significant differences in the areas under receiver operating characteristic curves between quantitative and visual analysis (p > 0.70). Linear regression analysis also indicated that quantitative assessments correlated well with visual semiquantitative assessments. CONCLUSIONS The findings of this study indicate that automatic quantitative analysis of exercise stress myocardial perfusion SPECT is similar to semiquantitative expert visual analysis for prognostic stratification. These findings may be of particular clinical importance in laboratories with less experienced visual interpreters.

Physical factors influencing quantitation of two-dimensional contrast echo amplitudes

Measurement errors that may interfere with quantitation by the new myocardial contrast two-dimensional echocardiographic technique were examined in a simplified in vitro model consisting of a 50 cc blood-filled balloon with supplemental controlled injection of 0.2 to 2.6 cc of sonicated dextrose 70%. The blood-contrast mixture in the balloon volume was imaged with two-dimensional echocardiography and discrete regions were studied for both magnitude and time course of echo intensities. Preliminary evidence indicates that a regional contrast echo intensity measurement is significantly modified by contrast-related ultrasound attenuation in intervening regions and by the amount and mode of contrast material injection. Thus, injection of 1.2 cc contrast material resulted in substantially higher peak echo intensity and a more rapid decay than injection of 0.8 or 0.6 cc. These measurements were also found to be influenced by the echographic system signal processing and time-gain compensation which contribute to nonlinear and unevenly compensated image distribution of echo amplitudes. Other factors are discussed, including transducer-related image resolution and image texture, contrast agent bubble size and persistence and computer methods for standardized selection of region of interest and analysis of the regional contrast intensity decay curve.

Reversal of chronic regional myocardial dysfunction (hibernating myocardium) by synchronized diastolic coronary venous retroperfusion during coronary angioplasty.

A 62 year old man with previous myocardial infarction, an occluded right coronary artery and a 90% stenosis of the left anterior descending coronary artery underwent angioplasty with the support of coronary venous retroperfusion of arterial blood during the procedure. In two of four angioplasty balloon dilations of the left anterior descending coronary artery, synchronized diastolic retroperfusion of the coronary veins with arterial blood was applied to protect the severely dysfunctioning myocardium from additional ischemia. Two-dimensional echocardiography was used to monitor and quantitate alterations in left ventricular function. Retroperfusion of arterial blood resulted in immediate improvement in ischemic zone wall motion despite the totally occluded artery during balloon dilation. Echocardiographic images recorded after angioplasty showed a marked improvement in contraction of the previously dyskinetic segments, with changes similar to those seen during balloon dilations with synchronized diastolic coronary venous retroperfusion. Thus, in this patient, viability of chronically dysfunctioning myocardium could be demonstrated by the improvement in regional wall motion during retroperfusion. This technique could eventually be of value to elucidate the anatomic location of viable myocardium while maintaining adequate left ventricular systolic function during coronary artery interventions in the catheterization laboratory.

Preservation of regional myocardial ultrasonic backscatter and systolic function during brief periods of ischemia by synchronized coronary venous retroperfusion

This study examines the effects of brief periods of ischemia on average and cardiac cycle-dependent variation of regional ultrasonic backscatter paralleled with changes in regional myocardial contraction, and to what extent these changes could be reversed by synchronized coronary venous retroperfusion. In five closed-chest dogs, the left anterior descending coronary artery was occluded on four occasions for a 2-minute period and retroperfusion was applied randomly to two of the coronary occlusions. Complete functional recovery was allowed between the occlusions. Two-dimensional echocardiographic images were obtained before and at the peak of the 2-minute occlusion period. Regional myocardial contraction as measured by fractional area change and systolic wall thickening during untreated occlusions decreased from 33.9 +/- 14.0% to -0.15 +/- 6.2%, and from 22.0 +/- 1.8% to -17.9 +/- 2.2%, whereas during retroperfusion-treated occlusions it changed from 37.4 +/- 8.5% to only 23.4 +/- 11.2% (p less than 0.005 versus baseline), and from 24.1 +/- 2.8% to only 12.7 +/- 2.0% (p less than 0.005 versus baseline), corresponding to a preservation of 62% and 52% of baseline regional contraction, respectively. Average regional gray level (arbitrary units) during untreated coronary occlusions exhibited a significant increase in the ischemic regions, from 5.6 +/- 2.7 at baseline to 11.5 +/- 4.4 during occlusion (p less than 0.005); during retroperfusion-treated occlusions, average gray level increased from 4.7 +/- 3.6 to only 6.3 +/- 3.6 (NS). Untreated coronary artery occlusions resulted in a systolic increase in gray level in the ischemic region, followed by a diastolic decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

New workstations for nuclear medicine

Modern nuclear medicine has benefitted from the recent development of more powerful and easier to use computer systems. The concept of a workstation, a powerful single user machine, has become feasible in recent years with the advent of high performance computers in relatively low cost and small packages. Furthermore local area networks using standard protocols have made the interconnection of multiple workstations from a single manufacturer routine, and soon will allow systems from multiple vendors to be integrated.Requirements for a new nuclear medicine workstation are best expressed in terms of which studies will it acquire and/or process, and the necessary throughput. In addition acceptance testing for computer equipment, patterned after the gamma camera test, is important. The systems available are mostly full function systems providing acquisition, processing, display and reporting capabilities, with a few providing acquisition only modules. By dedicating workstations to a particular task and thereby reducing the importance of unrelated functions cost can be minimized. The most important factors for stations doing clinical acquisition are image resolution, count rate capabilities, planar as well as SPECT capabilities, gated data acquisition for SPECT and planar studies, and possibly on the fly SPECT reconstruction and ease of operation. For stations assigned to processing studies, ease of operation, speed of the programs, the availability of clinical quantification procedures and SPECT reconstruction are important. Display and reporting stations require the highest image resolution and viewing area. Furthermore they must be optimized for quick review by busy physicians, implying that ease of operation and speed are paramount. Several current systems are examined and compared in terms of architecture, capabilities, and performance. The Siemens MaxDelta, DeltaManager and the integration of the soon to be released ICON provide an example of a server/client organization with a Digital Equipment VAX as the server. The ADAC Pegasys is based on a Sun workstation with special purpose stations for acquisition that communicate via Ethernet. The Picker Prism system uses a Stardent minisupercomputer based imaging workstation with a separate acquisition module. Several metrics will be presented which will allow the participants to judge aspects of different systems on their own. Productivity and indeed the future of nuclear medicine is in a large part controlled by the tools available. The current systems available (or soon to be) are dramatic improvements from the previous generation in the performance available, their graphical user interfaces, and their interconnectivity. Furthermore, the introduction of object oriented software development tools promises long term benefits for the developers by being able to reuse more software, and more effective methods for program design.

Echocardiographic assessment of coronary venous retroperfusion

Numerous interventions have been improvised in the last decade, all aiming to decrease cardiac mortality and morbidity following myocardial infarction by reducing infarct size. Aggressive revascularization interventions such as thrombolysis, percutaneous angioplasty and coronary bypass surgery, have recently been performed during the acute phase, with remarkably favorable results. However, it has been established that the myocardium usually will remain alive for only 3–6 hours after an acute coronary occlusion and, therefore, the most favorable results for maintaining viability of the jeopardized myocardium will be dependent on the time elapsed from the onset of symptoms to the achievement of revascularization. It has also been noted that the first 2–3 hours is the most critical period affecting viability of myocardium [1], Synchronized diastolic coronary venous retroperfusion using specially designed catheters and an electrocardiographically synchronized pump has been shown to immediately improve cardiac contractile and metabolic function and also reduce the infarct size after experimental coronary artery occlusion. This method has been proposed as a temporary clinical emergency treatment of acute myocardial ischemia, i.e., to provide support for periods of hours or days after an acute coronary occlusion, until other modes for permanent revascularization can be performed [2].