Kondapuram S. Sampathkumaran

Comparison of carbon-11-acetate with fluorine-18-fluorodeoxyglucose for delineating viable myocardium by positron emission tomography

OBJECTIVES This study was designed to determine in patients with advanced coronary disease whether prediction of recovery of mechanical function after coronary revascularization could be accomplished more effectively by positron emission tomography (PET) with carbon-11 (11C)-acetate than by PET with fluorine-18 (18F)-fluorodeoxyglucose. BACKGROUND Results of previous studies have demonstrated that preservation of myocardial oxidative metabolism (measured by PET with 11C-acetate) is necessary for recovery of systolic function after coronary revascularization. METHODS Myocardial oxidative metabolism was quantified before revascularization in 34 patients by the analysis of the rate of myocardial clearance of 11C-acetate. Metabolism of glucose was assessed by analysis of uptake of 18F-fluorodeoxyglucose. Receiver operating characteristic curves for predicting functional recovery were derived for the measurements of oxidative metabolism and glucose metabolism. In addition, criteria for prediction of recovery of function based on measurements of oxidative metabolism and glucose metabolism were developed and compared. RESULTS Analysis of receiver operating characteristic curves indicated that estimates of oxidative metabolism were more robust in predicting functional recovery than were estimates of glucose metabolism (p < 0.02). Moreover, threshold criteria with 11C-acetate exhibited superior positive and negative predictive values (67% and 89%, respectively) than did the criteria with 18F-fluorodeoxyglucose (52% and 81%, respectively), p < 0.01. In segments with initially severe dysfunction, estimates of oxidative metabolism tended to be more robust than estimates of glucose metabolism in predicting functional recovery. Moreover, in such segments, the threshold criteria with 11C-acetate tended to exhibit superior positive and negative predictive values (85% and 87%, respectively) than did the criteria with 18F-fluorodeoxyglucose (72% and 82%, respectively), although statistical significance was not achieved. CONCLUSIONS In patients with advanced coronary artery disease, the extent to which functional recovery can be anticipated after coronary revascularization can be delineated accurately by quantification of regional oxidative metabolism by PET with 11C-acetate.

Functional recovery after coronary revascularization for chronic coronary artery disease is dependent on maintenance of oxidative metabolism.

OBJECTIVES This study was performed to define the importance of maintenance of oxidative metabolism as a descriptor and determinant of functional recovery after revascularization in patients with left ventricular dysfunction attributable to chronic coronary artery disease. BACKGROUND Although myocardial accumulation of 18F-fluorodeoxyglucose indicates the presence of tissue that is metabolically active, it may not identify those metabolic processes required for restoration of myocardial contractility. Experimental studies suggest that, under conditions of ischemia and reperfusion, maintenance of myocardial oxidative metabolism is an important metabolic determinant of the capacity for functional recovery. METHODS In 16 patients positron emission tomography was performed to characterize myocardial perfusion (with H(2)15O), oxidative metabolism (with 11C-acetate) and utilization of glucose (with 18F-fluorodeoxyglucose). Dysfunctional but viable myocardium was differentiated from nonviable myocardium on the basis of assessments of regional function before and after coronary revascularization. To define the importance of coronary revascularization on myocardial perfusion and metabolism, tomography was repeated in 11 patients after revascularization. RESULTS Before revascularization, perfusion in 24 dysfunctional but viable myocardial segments and 29 nonviable segments averaged 79% and 74%, respectively, of that in 42 normal myocardial segments (both p less than 0.01). Dysfunctional but viable myocardium exhibited oxidative metabolism comparable to that in normal myocardium. In contrast, in nonviable myocardium, oxidative metabolism was only 66% of that in normal (p less than 0.01) and 69% of that in reversibly dysfunctional myocardium (p less than 0.003). Regional utilization of glucose normalized to regional perfusion in dysfunctional but viable myocardium was greater than that in normal myocardium (p less than 0.01). However, in both reversibly and persistently dysfunctional myocardium, utilization of glucose normalized to relative perfusion was markedly variable. CONCLUSIONS The results indicate that preservation of oxidative metabolism is a necessary condition for recovery of function after coronary recanalization in patients with chronic coronary artery disease. Consequently, approaches that measure myocardial oxygen consumption, such as dynamic positron emission tomography with 11C-acetate, should facilitate the identification of those patients most likely to benefit from coronary revascularization.

Dependence of recovery of contractile function on maintenance of oxidative metabolism after myocardial infarction

This study was performed to define the importance of maintenance of oxidative metabolism as a descriptor and determinant of the potential for functional recovery after revascularization in patients with recent myocardial infarction. In 11 patients (mean interval after infarction 6 days; 5 patients given thrombolytic therapy), positron emission tomography (PET) was performed to characterize myocardial perfusion (with oxygen-15-labeled water), glucose utilization (with fluorine-18-fluorodeoxyglucose) and oxidative metabolism (with carbon-11-acetate). Dysfunctional but viable myocardium was differentiated from nonviable myocardium by assessments of regional function before and after coronary revascularization. The impact of coronary revascularization on regional myocardial perfusion and metabolism was assessed in nine patients in whom tomography was repeated after revascularization. Before revascularization, dysfunctional but viable myocardium (19 segments) and nonviable myocardium (10 segments) exhibited relative perfusion equivalent to 74% and 63% of that of normal myocardium (33 segments), respectively (p less than 0.02). Dysfunctional but viable myocardium exhibited oxidative metabolism equivalent to 74% of that of normal myocardium (p less than 0.02). In contrast, in nonviable myocardium, oxidative metabolism was only 45% of that seen in normal (p less than 0.02) and 60% of that in reversibly dysfunctional myocardium (p less than 0.003). Regional glucose utilization (normalized to regional perfusion) in dysfunctional but viable myocardium was higher than that in normal myocardium (p less than 0.02). Nonviable myocardium exhibited lower levels of glucose utilization than did normal tissue (p less than 0.02). However, in both reversibly and persistently dysfunctional myocardium utilization of glucose normalized to relative perfusion was markedly variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Design and application of finite impulse response digital filters

The finite impulse response (FIR) digital filter is a spatial domain filter with a frequency domain representation. The theory of the FIR filter is presented and techniques are described for designing FIR filters with known frequency response characteristics. Rational design principles are emphasized based on characterization of the imaging system using the modulation transfer function and physical properties of the imaged objects. Bandpass, Wiener, and low-pass filters were designed and applied to 201T1 myocardial images. The bandpass filter eliminates low-frequency image components that represent background activity and high-frequency components due to noise. The Wiener, or minimum mean square error filter ‘sharpens’ the image while also reducing noise. The Wiener filter illustrates the power of the FIR technique to design filters with any desired frequency reponse. The lowpass filter, while of relative limited use, is presented to compare it with a popular elementary ‘smoothing’ filter.

Interactive digital filtering of gated cardiac studies during cine display

The use of a novel class of image processing hardware, the image computer, is illustrated by application to gated cardiac studies. Digital filtering of a nine-view study consisting of 144 frames, each 64x64 pixels in size, is performed using the Wiener filter. During image display the operator can change the filter parameters. Refiltering is then performed essentially instantaneously, permitting truly interactive filter selection. Comparable digital filtering using a fast conventional computer and display hardware is shown to be too slow to permit interactive filter modification. Image computers incorporate very large image memories with very tightly coupled, fast arithmetic processors and video display devices and allow very computation-intensive calculations to be performed interactively.

An efficient and cost effective nuclear medicine image network

An image network that is in use in a large nuclear medicine department is described. This network was designed to efficiently handle a large volume of clinical data at reasonable cost. Small, limited function computers are attached to each scintillation camera for data acquisition. The images are transferred by cable network or floppy disc to a large, powerful central computer for processing and display. Cost is minimized by use of small acquisition computers not equipped with expensive video display systems or elaborate analysis software. Thus, financial expenditure can be concentrated in a powerful central computer providing a centralized data base, rapid processing, and an efficient environment for program development. Clinical work is greatly facilitated because the physicians can process and display all studies without leaving the main reading area.

Hospital-wide distribution of nuclear medicine studies through a broadband digital network

Nuclear medicine provides a good environment for the evaluation of picture archiving and communication systems (PACS) because of the relatively small quantity of digital data that are generated, leading to reduced requirements for storage, display, and transmission compared with those found in radiology. The PACS in nuclear medicine is characterized by use of a single computer as a central storage, display, and analysis node. Images are acquired with use of small, low-cost computers attached to each camera. This network configuration offers advantages of convenience, but with great reliance on a single computer. A campus-wide picture network is under development at Washington University employing broadband cable television technology supplemented by baseband Ethernet (Digital Equipment Corp, Maynard, MA) components. All areas of diagnostic radiology and nuclear medicine are connected via a PACS testbed project. A radiology information system, supporting over 250 terminals, provides digital tracking of patients and report generation and retrieval. A new image workstation is under development in conjunction with Digital Equipment Corp. This system will permit display in multiple windows of report information and images from various modalities. A lung scan demonstration project is now beginning that is designed to test the value of a PACS in nuclear medicine. Digitally acquired chest radiographs will be displayed on an image workstation in nuclear medicine along with digital ventilation and perfusion lung scans. It is hoped that time-consuming logistic bottlenecks now encountered in lung scan interpretation will be reduced.