Resolution Positron Emission Tomography Imaging Research Articles

Association Between Mental Stress-Induced Inferior Frontal Cortex Activation and Angina in Coronary Artery Disease.

The inferior frontal lobe is an important area of the brain involved in the stress response, and higher activation with acute mental stress may indicate a more severe stress reaction. However, it is unclear if activation of this region with stress correlates with angina in individuals with coronary artery disease. Individuals with stable coronary artery disease underwent acute mental stress testing using a series of standardized speech/arithmetic stressors in conjunction with high resolution positron emission tomography imaging of the brain. Blood flow to the inferior frontal lobe was evaluated as a ratio compared with whole brain flow for each scan. Angina was assessed with the Seattle Angina Questionnaire's angina frequency subscale at baseline and 2 years follow-up. We analyzed 148 individuals with coronary artery disease (mean age [SD] 62 [8] years; 69% male, and 35.8% Black). For every doubling in the inferior frontal lobe activation, angina frequency was increased by 13.7 units at baseline ([Formula: see text], 13.7 [95% CI, 6.3-21.7]; P=0.008) and 11.6 units during follow-up ([Formula: see text], 11.6 [95% CI, 4.1-19.2]; P=0.01) in a model adjusted for baseline demographics. Mental stress-induced ischemia and activation of other brain pain processing regions (thalamus, insula, and amygdala) accounted for 40.0% and 13.1% of the total effect of inferior frontal lobe activation on angina severity, respectively. Inferior frontal lobe activation with mental stress is independently associated with angina at baseline and during follow-up. Mental stress-induced ischemia and other pain processing brain regions may play a contributory role.

Young Investigator Award session: Basic Science311Intraventricular flow patterns after percutaneous mitral valve repair with MitraClip implantation312Papillary muscles contribute significantly to shortening of dilated left ventricles313Relationship between cardiac uptake by 99mTc-DPD scintigraphy and left ventricular longitudinal strain in patients with transthyretin-related cardiac amyloidosis314Premature ventricular contraction in resynchronized patients with short atrio-ventricular delay: hemodynamic impact beyond A-wave truncation

Young Investigator Award session: Basic Science311Intraventricular flow patterns after percutaneous mitral valve repair with MitraClip implantation312Papillary muscles contribute significantly to shortening of dilated left ventricles313Relationship between cardiac uptake by 99mTc-DPD scintigraphy and left ventricular longitudinal strain in patients with transthyretin-related cardiac amyloidosis314Premature ventricular contraction in resynchronized patients with short atrio-ventricular delay: hemodynamic impact beyond A-wave truncation

Patient motion effects on the quantification of regional myocardial blood flow with dynamic PET imaging.

Patient motion is a common problem during dynamic positron emission tomography (PET) scans for quantification of myocardial blood flow (MBF). The purpose of this study was to quantify the prevalence of body motion in a clinical setting and evaluate with realistic phantoms the effects of motion on blood flow quantification, including CT attenuation correction (CTAC) artifacts that result from PET-CT misalignment. A cohort of 236 sequential patients was analyzed for patient motion under resting and peak stress conditions by two independent observers. The presence of motion, affected time-frames, and direction of motion was recorded; discrepancy between observers was resolved by consensus review. Based on these results, patient body motion effects on MBF quantification were characterized using the digital NURBS-based cardiac-torso phantom, with characteristic time activity curves (TACs) assigned to the heart wall (myocardium) and blood regions. Simulated projection data were corrected for attenuation and reconstructed using filtered back-projection. All simulations were performed without noise added, and a single CT image was used for attenuation correction and aligned to the early- or late-frame PET images. In the patient cohort, mild motion of 0.5 ± 0.1 cm occurred in 24% and moderate motion of 1.0 ± 0.3 cm occurred in 38% of patients. Motion in the superior/inferior direction accounted for 45% of all detected motion, with 30% in the superior direction. Anterior/posterior motion was predominant (29%) in the posterior direction. Left/right motion occurred in 24% of cases, with similar proportions in the left and right directions. Computer simulation studies indicated that errors in MBF can approach 500% for scans with severe patient motion (up to 2 cm). The largest errors occurred when the heart wall was shifted left toward the adjacent lung region, resulting in a severe undercorrection for attenuation of the heart wall. Simulations also indicated that the magnitude of MBF errors resulting from motion in the superior/inferior and anterior/posterior directions was similar (up to 250%). Body motion effects were more detrimental for higher resolution PET imaging (2 vs 10 mm full-width at half-maximum), and for motion occurring during the mid-to-late time-frames. Motion correction of the reconstructed dynamic image series resulted in significant reduction in MBF errors, but did not account for the residual PET-CTAC misalignment artifacts. MBF bias was reduced further using global partial-volume correction, and using dynamic alignment of the PET projection data to the CT scan for accurate attenuation correction during image reconstruction. Patient body motion can produce MBF estimation errors up to 500%. To reduce these errors, new motion correction algorithms must be effective in identifying motion in the left/right direction, and in the mid-to-late time-frames, since these conditions produce the largest errors in MBF, particularly for high resolution PET imaging. Ideally, motion correction should be done before or during image reconstruction to eliminate PET-CTAC misalignment artifacts.

Glucose metabolism in the human cerebellum: anatomical-functional correlations.

Functional maturation of human cerebellar structures was previously difficult to evaluate with positron emission tomography (PET) because of scanner resolution. Only vermis and cerebellar hemispheres could be reliably identified with 2-deoxy-2[18F]fluoro-D-glucose (FDG) PET. In the present study, we have used a new high resolution PET system, the Siemens EXACT-HR, to study, in depth, the patterns of glucose metabolism in various cerebellar structures. Due to the orientation of the cerebellar fissures which are important landmarks, the largest number of regions could be identified when the cerebellar regions were displayed on coronal planes. The high resolution PET images, together with magnetic resonance imaging (MRI) data and standard atlases, now allow identification of the following cerebellar structures: anterior vermis, posterior vermis, dentate nucleus, anterior lobe, posterior quadrangular lobule, superior semilunar lobule, inferior semilunar, gracile, and biventer lobules, tonsil, and cerebellar white matter. These cerebellar regions are displayed in an atlas format together with magnetic resonance images to allow easy identification. The present study is a prerequisite for detailed PET analyses of cerebellar metabolism in children with diseases of the cerebellum.

Nitroimidazoles for imaging hypoxic myocardium.

A series of radiopharmaceuticals that incorporate nitroimidazole moieties have been synthesized to detect decreased local tissue pO2. In contrast to agents that localize in proportion to perfusion, these agents concentrate in hypoxic tissue. Myocardium with an intracellular pO2 < 3 mm Hg (about 25% of normal), which has lost its contractile ability but has maintained its ability to catabolize glucose, can be localized with this imaging technique. When a nitroimidazole enters a viable cell, the molecule undergoes a series of reactions: Initially, the molecule gains a single electron by an enzymatic process in the cytoplasm to form a potentially reactive species, then in the presence of adequate intracellular oxygen levels the molecule is reoxidized. These reactions are repeated until the intact molecule diffuses back out of the cell. In myocytes with reduced oxygen concentration, the reoxidation does not take place, the reactive species appears to undergo additional reduction reactions and remains in the cell. The association of the reduced nitroimidazole and other cellular elements is not irreversible, since these agents clear from hypoxic tissue with a half-life of 4 to 8 hours. In one of the first nitroimidazoles used for in vivo imaging, fluoromisonidazole was the radiopharmaceutical. Two major problems with fluoromisonidazole are its relatively low concentration within the lesion and the need to wait several hours to permit clearance of the agent from the normoxic background tissue (contrast between lesion and background typically < 2:1 at about 90 minutes after injection). Even with high resolution positron emission tomography imaging, this combination of circumstances makes successful evaluation of hypoxic lesions a challenge. The development of single photon agents with longer physical half-lives and comparable biologic properties offer a greater opportunity for successful imaging. In 1992 technetium 99m-labeled nitroimidazoles were described that had in vivo kinetics that were potentially suitable for detection of hypoxic myocardium. Laboratory studies showed preferential binding of these agents to hypoxic myocytes and isolated hearts in vitro and to ischemic myocardial tissue in laboratory animals. Patient studies are planned to determine whether the promise of these agents in laboratory studies can be realized in clinical practice.

Constrained least squares filtering in high resolution PET and SPECT imaging

Constrained least-squares filtering is a technique which employs a priori tomograph response information for the filtering of projection data prior to the filtered backprojection of radionuclide distribution images. A simulation study in which the performance of this algorithm was evaluated as a function of the sampling density within each projection of the radon transform is described. The results of this evaluation demonstrate that the efficient application of this algorithm requires higher sampling densities than are typically employed in high-resolution PET (positron emission tomography) and SPECT (single-photon-emission computed tomography). Therefore, application of this algorithm requires software and/or hardware modification of the data acquisition schemes employed in tomographic systems. >