Cardiac Positron Emission Tomography Imaging Research Articles

Cardiac positron emission tomography imaging with [ 11c]hydroxyephedrine, a specific tracer for sympathetic nerve endings, and its functional correlates in congestive heart failure

The integrative mechanisms of autonomic dysfunction in congestive heart failure (CHF) remain poorly understood. We sought to study cardiac retention of [ 11C]hydroxyephedrine (HED), a specific tracer for sympathetic presynaptic innervation, and its functional correlates in CHF. Thirty patients with mild to moderate heart failure underwent resting cardiac HED positron emission tomography imaging, spectrum analysis testing of systolic pressure and heart rate variability in the resting supine and 70° head-up tilt positions, and testing of baroreflex sensitivity. Compared with control subjects, global myocardial HED retention index was reduced by 30% (p <0.01) in patients with CHF. The HED retention index did not correlate significantly with heart rate variability. However, it correlated with baroreflex sensitivity at rest (r = 0.43, p = 0.05) and with systolic pressure low-frequency (0.03 to 0.15 Hz) variability at head-up tilt (r = 0.76, p <0.01), as well as with low-frequency systolic pressure variability response from baseline to tilt (r = 0.75, p <0.01). We conclude that cardiac HED retention is reduced in patients with CHF. This correlates with blunted vascular sympathetic effector responses during posture-induced reflex activation and baroreflex control of heart rate, suggesting an interdependence between cardiac presynaptic innervation abnormalities and neural mechanisms important to blood pressure maintenance in CHF.

Alignment of dynamic cardiac PET images for correction of motion

A technique was developed to align images from dynamic cardiac N-13 ammonia positron emission tomography (PET) scans. Inaccurate alignment of images from these scans stems from breathing, motion of the heart within the thorax, and overall motion of the patient (particularly during pharmacologic stress). The images from these scans represent changing distributions, from high blood pool concentrations to predominantly myocardial uptake, and are generally noisy. In this technique, templates are defined from a long, late frame (5-10 min). These templates include a myocardial template, which matches late frames, a blood pool template, which matches frames in which the left ventricle blood pool is dominant, and a modified blood pool template, which reduces the effect of activity in the right ventricle. The correlation function is used as the maximized parameter over shifts between each three-dimensional image frame and the appropriate template. The technique was tested on phantom, human, and animal data with myocardial defects. Phantom data showed the technique to be reliable to within one voxel (1.7/spl times/1.7/spl times/4.2 mm/sup 3/), and motion which was apparent in human data was reduced significantly. Blood flow values measured from corrected data showed two traits: higher values, due to better matching regions of interest to images, and better fits, due to smoother time-activity curves.

Evaluation of simulation-based scatter correction for 3-D PET cardiac imaging

Quantitative imaging of the human thorax poses one of the most difficult challenges for three-dimensional (3-D) (septaless) positron emission tomography (PET), due to the strong attenuation of the annihilation radiation and the large contribution of scattered photons to the data. In [/sup 18/F] fluorodeoxyglucose (FDG) studies of the heart with the patient's arms in the field of view, the contribution of scattered events can exceed 50% of the total detected coincidences. Accurate correction for this scatter component is necessary for meaningful quantitative image analysis and tracer kinetic modeling. For this reason, the authors have implemented a single-scatter simulation technique for scatter correction in positron volume imaging. Here, they describe this algorithm and present scatter correction results from human and chest phantom studies.

A Novel Surface Reconstruction and Display Method for Cardiac PET Imaging

Positron emission tomography (PET) allows the in vivo assessment of biochemical activity in humans. The newer PET cameras can create several imaging planes, or slices, through an organ inside the body. The interpretation of two-dimensional (2-D) slices of an organ is often difficult for the clinician since he or she has to form a three-dimensional (3-D) mental composite of the structure of interest. We have developed a set of algorithms to reconstruct a functional three-dimensional surface model of the cardiac left ventricle from a set of two-dimensional cross-sectional image slices generated by PET. The theoretical techniques for this reconstruction method are applicable to most organs provided that the appropriate models for the organs are considered. An automatic boundary detection algorithm outlines the surface of the left ventricle from the 2-D images and assigns intensity values to the surface points whose level is proportional to the local activity. A 3-D surface of the intensity levels, with pseudocolor enhancement, is then displayed with the long axis of the heart in a vertical position. Such a display allows the 3-D myocardial tracer uptake to be clearly visualized by the clinician for better diagnosis.