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The purpose of this chapter is to introduce the reader to the fundamentals of image processing in Nuclear Medicine. It is not meant as a comprehensive guide, but more as an overview and introduction to those topics important to understanding the various forms of image processing.

Objectives The aim of this study was to determine whether post-traumatic stress disorder (PTSD) is associated with coronary heart disease (CHD) using a prospective twin study design and objective measures of CHD. Background It has long been hypothesized that PTSD increases the risk of CHD, but empirical evidence using objective measures is limited. Methods We conducted a prospective study of middle-aged male twins from the Vietnam Era Twin Registry. Among twin pairs without self-reported CHD at baseline, we selected pairs discordant for a lifetime history of PTSD, pairs discordant for a lifetime history of major depression, and pairs without either condition. All underwent a clinic visit after a median follow-up of 13 years. Outcomes included clinical events (myocardial infarction, other hospitalizations for CHD and coronary revascularization) and quantitative measures of myocardial perfusion by [13N] ammonia positron emission tomography, including a stress total severity score and coronary flow reserve. Results A total of 562 twins (281 pairs) with a mean age of 42.6 years at baseline were included in this study. The incidence of CHD was more than double in twins with PTSD (22.6%) than in those without PTSD (8.9%; p Conclusions Among Vietnam-era veterans, PTSD is a risk factor for CHD.

Explicit fusion of perfusion data from Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) with coronary artery anatomy from Computed Tomographic Coronary Angiography (CTA) has been shown to improve the diagnostic yield for coronary artery disease (CAD) compared to either modality alone. However, most clinically available methods were developed for multimodal scanners or require interactive alignment prior to display and analysis. A new approach was developed to register the two distributions obtained either from a single multimodal imager or from separate scanners, and a preliminary validation was undertaken to compare the automatic alignment to interactive alignment by two experts.

Hybrid positron emission tomography (PET) and computed tomography (CT) scanners were introduced in the late 1990s. Hybrid imagers were first used for oncology and were widely accepted for their unique ability to merge high-resolution anatomy with F-fluorodeoxyglucose (FDG) as a functional tumor agent. For cardiac applications, the CT data was useful only for attenuation correction, as the motion of the heart caused significant artifacts in the thoracic images of the mediastinum from the single slice CTs in these early scanners. Multidetector CT scanners for high-resolution cardiac imaging were integrated into hybrid systems starting in about 2002. For the first time it appeared that high-resolution cardiac anatomy would be easily correlated to myocardial perfusion images (MPI) using the same imager to acquire both images in a single scanning session. However, it soon became apparent that thoracic CTs obtained from hybrid scanners were not necessarily in registration with the serially acquired PET, and some adjustments had to be made for these differences. Misalignment of emission and x-ray CT images is a particular challenge in the thoracic cavity due to motion of the diaphragm, heart, abdominal organs, and bony structures, which are not consistently represented in the two studies. In attenuation correction, breathing motion is generally considered the main problem; transmission and emission scan misalignment is most noticeable at the left lung/left-ventricle interface where myocardial uptake overlies the left lung of the CT on fused images as well as at the lung/diaphragm interface where tissue in the transmission scan may or may not be present at the lung/diaphragm interface of the emission. When considering fusion for correlating anatomy and physiology, breathing motion is definitely a problem, but cardiac motion is concerning for additional reasons. Generally, coronary arteries are observed best on only a few frames of the dynamic computed tomographic angiogram (CTA) study (and in some protocols, only one frame is acquired). The nuclear study is generally summed to improve signal-to-noise prior to visual or quantitative analysis. Thus, there is an inherent mismatch between the hearts as imaged in the PET and CT. In addition, the first attempts to display these images simply used overlay techniques, similar to what was being done for oncology. However, the correlation of the perfusion information with the coronary anatomy could not be properly appreciated in a slice-by-slice display, or could quantitation of the perfusion studies be easily included. To address the challenge of correcting transmission and emission misalignment for attenuation correction, several groups have suggested solutions including breathing instructions during the CT acquisition, modifying the CT protocol to allow for free-breathing, and retrospective or post-processing registration techniques. For fusion of CTA and MPI, special alignment techniques have been developed for registering the two images, since nearly perfect alignment is important for diagnostic purposes. Given that such post-acquisition registration software may be needed for hybrid systems, investigation into its use for aligning studies acquired from separate machines is also being performed. Finally, high resolution displays showing 3D coronary anatomy concurrently with 3D perfusion information, including quantitative analysis of perfusion defects, are being perfected and their importance for CAD diagnosis is being demonstrated. These topics are addressed in the following sections.

Myocardial perfusion imaging using nuclear cardiology techniques has enjoyed widespread clinical use because of its well-documented diagnostic accuracy for assessing coronary artery disease. Industry has begun to create innovative designs of dedicated cardiac single photon emission CT (SPECT) scanners that constrain all detector area to imaging just the heart. New software has also been implemented, which recovers image resolution and limits image noise. Myocardial perfusion positron emission tomography (PET) imaging is experiencing unprecedented growth as evidence mounts of superior cardiac diagnostic performance over SPECT. Advances in PET have been made in gantry and detector design. Improvements in gantry design have been focused on hybrid PET/CT imaging. Improvements in detector design have consisted of using new scintillation crystals and in moving from two- to three-dimensional imaging. These SPECT and PET innovations are resulting in shorter study time and/or reduced radiation dose to the patient and in promoting easier scheduling, higher patient satisfaction, and importantly, higher image quality.

In humans, the wakeful resting condition is characterized by a default mode of brain function involving high levels of activity within a functionally connected network of brain regions. This network has recently been implicated in mental self-projection into the past, the future, or another individual's perspective. Here we use [ 18 F]-fluorodeoxyglucose positron emission tomography imaging to assess resting-state brain activity in our closest living relative, the chimpanzee, as a potential window onto their mental world and compare these results with those of a human sample. We find that, like humans, chimpanzees show high levels of activity within default mode areas, including medial prefrontal and medial parietal cortex. Chimpanzees differ from our human sample in showing higher levels of activity in ventromedial prefrontal cortex and lower levels of activity in left-sided cortical areas involved in language and conceptual processing in humans. Our results raise the possibility that the resting state of chimpanzees involves emotionally laden episodic memory retrieval and some level of mental self-projection, albeit in the absence of language and conceptual processing.

Single photon emission computed tomography (SPECT) myocardial perfusion imaging has attained widespread clinical acceptance as a standard of care for patients with known or suspected coronary artery disease. A significant contribution to this success has been the use of computer techniques to provide objective quantitative assessment in interpreting these studies. We have implemented the Emory Cardiac Toolbox (ECTb) as a pipeline to distribute the software tools that we and others have researched, developed, and validated to be clinically useful so that diagnosticians everywhere can benefit from our work. Our experience has demonstrated that integration of all software tools in a common platform is the optimal approach to promote both accuracy and efficiency. Important attributes of the ECTb approach are (1) our extensive number of normal perfusion databases for SPECT and positron emission tomography (PET) studies, each created with at least 150 patients; (2) our use of Fourier analysis of regional thickening to ensure proper temporal resolution and to allow accurate measurement of left ventricular function and dyssynchrony; (3) our development of PET tools to quantify myocardial hibernation and viability; (4) our development of 3-dimensional displays and the use of these displays as a platform for image fusion of perfusion and computed tomography angiography; and (5) the use of expert systems for decision support. ECTb is an important tool for extracting quantitative parameters from all types of cardiac radionuclide distributions. ECTb should continue to play an important role in establishing cardiac SPECT and PET for flow, function, metabolism, and innervation clinical applications.

A count-based method using technetium-99m sestamibi electrocardiography-gated myocardial perfusion single photon emission computed tomography imaging has been developed to extract the left ventricular (LV) regional phase of contraction (onset of mechanical contraction [OMC]) throughout the cardiac cycle. This study was performed to develop OMC normal databases and dynamic OMC displays for assessment of cardiac mechanic dyssynchrony.LV regional phases were extracted from 90 enrolled normal subjects (45 men and 45 women) by use of the Emory Cardiac Toolbox and then submitted to statistical analysis to generate the normal databases. The LV OMC wave was dynamically propagated over the perfusion polar map by blackening either sequential phase bins or all past phases. The developed OMC normal databases consisted of peak phase (134.5 degrees +/- 14.3 degrees for men and 140.2 degrees +/- 14.9 degrees for women), phase SD (14.2 degrees +/- 5.1 degrees for men and 11.8 degrees +/- 5.2 degrees for women), and phase histogram bandwidth (38.7 degrees +/- 11.8 degrees for men and 30.6 degrees +/- 9.6 degrees for women), skewness (4.19 +/- 0.68 for men and 4.60 +/- 0.72 for women), and kurtosis (19.72 +/- 7.68 for men and 23.21 +/- 8.16 for women). Both statistical analysis and dynamic OMC displays were incorporated into a user interface as a diagnostic tool.The OMC normal databases and dynamic OMC displays should help clinicians evaluate cardiac mechanic dyssynchrony. Prospective clinical trials are needed to validate whether this tool can be used to select patients with severe heart failure symptoms who might benefit from cardiac resynchronization therapy.

New algorithms were evaluated for their efficacy in detecting and quantifying serial changes in myocardial perfusion from single photon emission computed tomography (SPECT).We generated 72 simulations with various left ventricular positions, sizes, count rates, and perfusion defect severities using the nonuniform rational B-splines (NURBs)-based CArdiac Torso (NCAT) phantom. Images were automatically aligned by use of both full linear and rigid transformations and quantified for perfusion by use of the CEqual program. Changes within a given perfusion defect were compared by use of a Student t test before and after registration. Registration approaches were compared by use of receiver operating characteristic analysis. Changes of 5% were not detected well in single patients with or without alignment. Changes of 10% and 15% could be detected with false-positive rates of 15% and 10%, respectively, in single studies if alignment was performed before perfusion analysis. Alignment also reduced the number of studies necessary to demonstrate a significant perfusion change (P.05) in groups of patients by about half.Comparison of mean uptake by t values in SPECT perfusion defects can be used to detect 10% and greater differences in serial perfusion studies of single patients. Image alignment is necessary to optimize automatic detection of perfusion changes in both single patients and groups of patients.

The purpose of this study was to determine the independent value of left ventricular (LV) functional parameters derived from gated fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) to predict prognosis in patients with ischemic cardiomyopathy undergoing myocardial viability assessment. We studied 90 consecutive patients with coronary artery disease and low LV ejection fraction (26% ± 7%) undergoing gated FDG PET to assess myocardial viability for potential revascularization. The primary endpoint for this analysis was the occurrence of cardiac death, myocardial infarction, or worsening heart failure (HF) to New York Heart Association class IV. During follow-up (22 ± 14 months), 21 patients had an event (17 died, 4 had myocardial infarctions, and 4 had worsening HF). On Cox regression analysis, the event-free survival rate at 2 years was lower for patients with an end-diastolic volume (EDV) of 260 mL or greater (relative risk, 2.7; P = .014), end-systolic volume (ESV) of 200 mL or greater (relative risk, 2.5; P = .021), and LV mass of 143 g or greater (relative risk, 1.6; P = .009). In a risk-adjusted model, EDV (_x2 = 68, P < .0001) and ESV (x 2 = 75, P = .035) added a significant amount in the estimation of events over the perfusion-FDG mismatch pattern (x 2 = 40, P < .001). In a stratified Cox model, patients with PET mismatch, LV ejection fraction lower than 25%, and EDV of 260 mL or greater had the lowest survival rate (P = .006). These patients showed an apparent survival benefit with revascularization but without an improvement in HF symptoms. LV functional parameters determined by gated FDG PET have incremental prognostic value over viability information in patients with ischemic cardiomyopathy. Our data suggest that patients with residual viability and advanced cardiac remodeling are at high clinical risk. In these patients the apparent survival benefit of revascularization may not be associated with a measurable improvement in HF symptoms.

The quality of a Teboroxime single-photon emission computed tomography (SPECT) study can be degraded by Teboroxime's rapid myocardial washout and high liver uptake. Described is the use of fast-fanning acquisition and nonlinear regression with distance penalty (NLRDP) to compensate for the two effects. Tl-201/conventional single-rotation Sestamibi (MIBI) and Tl-201/dynamic fast-fanning Teboroxime (TEBO) rest/stress acquisitions were conducted on 18 subjects. TEBO reconstructions were processed by NLRDP using group-averaged kinetics to separate images into liver, myocardium, and background. Reprojections of these compartments were registered with the measured projections. This made possible the extraction of patient-specific kinetics. NLRDP identified defects (abnormal myocardium with different kinetics from normal tissue) by differences in the kinetics of the defect pixels. Enhanced-TEBO (E-TEBO) images were produced by using the kinetic curves to calculate the Teboroxime concentration in each pixel at the time of expected peak myocardial uptake and by omitting the liver compartment. Stress and reversibility total severity scores and total impaired and reversible myocardial mass were computed for the MIBI, TEBO, and E-TEBO images using the Emory Cardiac Toolbox. Regression and correlation analyses of these quantitative indices indicate that Teboroxime SPECT can produce results similar to those of Sestamibi SPECT if E-TEBO images are generated.

In today's cost containment environment it is important to consider changes to standard protocols which would reduce cost, particularly if there is no significant loss of diagnostic accuracy. The aim of the present study was to assess the usefulness of a gated stress-only Tc sestamibi protocol in comparison to conventional gated dual isotope rest-stress myocardial perfusion single photon emission computed tomography (SPECT) in the detection and localization of coronary artery disease (CAD). Sixty-five consecutive patients (65+/-10 years, 22 women) who had undergone conventional gated perfusion SPECT were chosen retrospectively. Fifty-three of these 65 patients had previous coronary arteriography, 45 with at least one stenosis, eight without stenosis, and 12 of these 65 patients had

Introduccion y objetivos Integrar la informacion anatomica y funcional en pacientes con cardiopatia isquemica es una tarea habitual en la practica diaria del cardiologo. El objetivo de este trabajo es presentar una metodologia de unificacion tridimensional de la informacion anatomica relativa a las coronarias epicardicas, proveniente de la coronariografia, con la informacion fisiologica de perfusion tisular procedente de la tomogammagrafia de perfusion miocardica. Metodos Se seleccionaron 3 pacientes programados, por criterios clinicos, para revascularizacion coronaria percutanea y con enfermedad de un solo vaso (descendente anterior, coronaria derecha y circunfleja). Las imagenes coronariograficas biplanares se obtuvieron antes y despues de la dilatacion. Durante la oclusion coronaria se administro una dosis de 99mTc-tetrofosmina y, una vez finalizada la dilatacion, se obtuvieron las imagenes de perfusion miocardica correspondientes a la oclusion. La tomogammagrafia de control en reposo se repitio dos dias despues. Mediante una metodologia propia se generaron los contornos epicardicos de las imagenes de perfusion miocardica y sobre ellos se superpuso el arbol coronario tridimensional proveniente de la coronariografia. Resultados Se logro una correcta reconstruccion tridimensional del contorno epicardico y del arbol coronario completo en los 3 pacientes. La imagen unificada en tres dimensiones presento una excelente concordancia entre la extension de los defectos de perfusion y la distribucion anatomica del vaso ocluido. Conclusiones La superposicion tridimensional de las imagenes de perfusion miocardica y de la coronariografia es tecnicamente posible. Ello permite integrar la informacion anatomica y funcional de cara a facilitar la toma de decisiones por parte del cardiologo y mejorar el manejo del paciente coronario.

The left ventricular myocardium plays a key role in the entire circulation system and an automatic delineation of the myocardium is a prerequisite for most of the subsequent functional analysis. In this paper, we present a complete system for an automatic segmentation of the left ventricular myocardium from cardiac computed tomography (CT) images using the shape information from images to be segmented. The system follows a coarse-to-fine strategy by first localizing the left ventricle and then deforming the myocardial surfaces of the left ventricle to refine the segmentation. In particular, the blood pool of a CT image is extracted and represented as a triangulated surface. Then, the left ventricle is localized as a salient component on this surface using geometric and anatomical characteristics. After that, the myocardial surfaces are initialized from the localization result and evolved by applying forces from the image intensities with a constraint based on the initial myocardial surface locations. The proposed framework has been validated on 34-human and 12-pig CT images, and the robustness and accuracy are demonstrated.

We reported previously that mean quantified cardiac functional parameters computed by one gated single photon emission computed tomography (SPECT) technique were not significantly altered by common gating errors. However, it is not known to what extent other gated SPECT approaches that are based on different ventricular modeling assumptions are influenced by arrhythmias, nor are the effects of gating errors on visual analyses and their subsequent clinical implications known.Projection data for 50 patients (aged 64 +/- 12 years; 68% men; 76% with myocardial perfusion defects) undergoing technetium-99m sestamibi gated SPECT who were in sinus rhythm during data acquisition were altered to simulate common arrhythmias. To determine quantitative effects, we performed calculations for original control and altered images by Gaussian myocardial detection (Quantitative Gated SPECT [QGS] program) and by wall thickening derived from gated perfusion polar maps (Emory Cardiac Toolbox program). To evaluate visual assessment in control and simulated-arrhythmia tomograms, 2 experienced blinded observers independently interpreted perfusion from polar maps and wall motion and thickening from tomographic cines, using a 4-point scale.Although mean functional parameters were scarcely altered, paired t tests showed ejection fraction fluctuations to be significantly different from control values, causing patients to change between abnormal and normal ejection fraction categories (2% of patients by QGS and 14% by Emory Cardiac Toolbox). Visual examination of QGS polar perfusion and function maps showed changes for 72% of cases, although in only 4% were these considered to have potential clinical consequences. The kappa statistic for visual analysis of concordance between control and arrhythmia readings showed that agreement was "excellent" for perfusion, "good" for motion, and "marginal" for thickening.As with quantitative measurements, thickening is the parameter most prone to error in the presence of arrhythmias. It is important to test data for gating errors to avoid potentially erroneous measurements and visual readings.

Summary: Purpose: To measure vagus nerve stimulation (VNS)-induced cerebral blood flow (CBF) effects after prolonged VNS and to compare these effects with immediate VNS effects on CBF. Methods: Ten consenting partial epilepsy patients had positron emission tomography (PET) with intravenous [15O]H2O. Each had three control scans without VNS and three scans during 30 s of VNS, within 20 h after VNS began (immediate-effect study), and repeated after 3 months of VNS (prolonged study). After intrasubject subtraction of control from stimulation scans, images were anatomically transformed for intersubject averaging and superimposed on magnetic resonance imaging (MRI) for anatomic localization. Changes on t-statistical maps were considered significant at p < 0.05 (corrected for multiple comparisons). Results: During prolonged studies, CBF changes were not observed in any regions that did not have CBF changes during immediate-effect studies. During both types of studies, VNS-induced CBF increases were similarly located in the bilateral thalami, hypothalami, inferior cerebellar hemispheres, and right postcentral gyrus. During immediate-effect studies, VNS decreased bilateral hippocampal, amygdalar, and cingulate CBF and increased bilateral insular CBF; no significant CBF changes were observed in these regions during prolonged studies. Mean seizure frequency decreased by 25% over a 3-month period between immediate and prolonged PET studies, compared with 3 months before VNS began. Conclusions: Seizure control improved during a period over which some immediate VNS-induced CBF changes declined (mainly over cortical regions), whereas other VNS-induced CBF changes persisted (mainly over subcortical regions). Altered synaptic activities at sites of persisting VNS-induced CBF changes may reflect antiseizure actions.

Prognosis and diagnosis of cardiac diseases frequently require quantitative evaluation of the ventricle volume, mass, and ejection fraction. The delineation of the myocardial wall is involved in all of these evaluations, which is a challenging task due to large variations in myocardial shapes and image quality. In this paper, we present an automatic method for extracting the myocardial wall of the left and right ventricles from cardiac CT images. In the method, the left and right ventricles are located sequentially, in which each ventricle is detected by first identifying the endocardium and then segmenting the epicardium. To this end, the endocardium is localized by utilizing its geometric features obtained on-line from a CT image. After that, a variational region-growing model is employed to extract the epicardium of the ventricles. In particular, the location of the endocardium of the left ventricle is determined via using an active contour model on the blood-pool surface. To localize the right ventricle, the active contour model is applied on a heart surface extracted based on the left ventricle segmentation result. The robustness and accuracy of the proposed approach is demonstrated by experimental results from 33 human and 12 pig CT images.

VISUALLY guided reaching requires complex neural transformations to link visual and proprioceptive inputs with appropriate motor outputs1,2. Despite the complexity of these transformations, hand–eye coordination in humans is remarkably flexible, as demonstrated by the ease with which reaching can be adapted to distortions in visual feedback. If subjects attempt to reach to visual targets while wearing displacing prisms, they initially misreach in the direction of visual displacement. Given feedback about their reaching errors, however, they quickly adapt to the visual distortion. This is shown by the gradual resumption of accurate reaching while the prisms remain in place, and by the immediate onset of reaching errors in the opposite direction after the prisms have been removed3. Despite an abundance of psy-chophysical data on adaptation to prisms, the functional localization of this form of sensorimotor adaptation is uncertain. Here we use positron emission tomography (PET) to localize changes in regional cerebral blood flow (rCBF) in subjects who performed a prism-adaptation task as well as a task that controlled for the sensory, motor and cognitive conditions of the adaptation experiment. Difference images that reflected the net effects of the adaptation process showed selective activation of posterior parietal cortex contralateral to the reaching limb.

We propose an automatic method for localizing the LV from CT images by using surface segmentation on the heart surface. The robustness of this method has been demonstrated by results from 34 CT images.

OBJECTIVE Left ventricular (LV) function and dyssynchrony parameters measured from serial gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) using blinded processing had a poorer repeatability than when manual side-by-side processing was used. The objective of this study was to validate whether an automatic alignment tool can reduce the variability of LV function and dyssynchrony parameters in serial gated SPECT MPI. METHODS Thirty patients who had undergone serial gated SPECT MPI were prospectively enrolled in this study. Thirty minutes after the first acquisition, each patient was repositioned and a gated SPECT MPI image was reacquired. The two data sets were first processed blinded from each other by the same technologist in different weeks. These processed data were then realigned by the automatic tool, and manual side-by-side processing was carried out. All processing methods used standard iterative reconstruction and Butterworth filtering. The Emory Cardiac Toolbox was used to measure the LV function and dyssynchrony parameters. RESULTS The automatic tool failed in one patient, who had a large, severe scar in the inferobasal wall. In the remaining 29 patients, the repeatability of the LV function and dyssynchrony parameters after automatic alignment was significantly improved from blinded processing and was comparable to manual side-by-side processing. CONCLUSION The automatic alignment tool can be an alternative method to manual side-by-side processing to improve the repeatability of LV function and dyssynchrony measurements by serial gated SPECT MPI.

The aim of this study was to determine whether post-traumatic stress disorder (PTSD) is associated with coronary heart disease (CHD) using a prospective twin study design and objective measures of CHD.It has long been hypothesized that PTSD increases the risk of CHD, but empirical evidence using objective measures is limited.We conducted a prospective study of middle-aged male twins from the Vietnam Era Twin Registry. Among twin pairs without self-reported CHD at baseline, we selected pairs discordant for a lifetime history of PTSD, pairs discordant for a lifetime history of major depression, and pairs without either condition. All underwent a clinic visit after a median follow-up of 13 years. Outcomes included clinical events (myocardial infarction, other hospitalizations for CHD and coronary revascularization) and quantitative measures of myocardial perfusion by [(13)N] ammonia positron emission tomography, including a stress total severity score and coronary flow reserve.A total of 562 twins (281 pairs) with a mean age of 42.6 years at baseline were included in this study. The incidence of CHD was more than double in twins with PTSD (22.6%) than in those without PTSD (8.9%; p0.001). The association remained robust after adjusting for lifestyle factors, other risk factors for CHD, and major depression (odds ratio: 2.2; 95% confidence interval: 1.2 to 4.1). Stress total severity score was significantly higher (+95%, p = 0.001) and coronary flow reserve was lower (-0.21, p = 0.02) in twins with PTSD than in those without PTSD, denoting worse myocardial perfusion. Associations were only mildly attenuated in 117 twin pairs discordant for PTSD.Among Vietnam-era veterans, PTSD is a risk factor for CHD.

Nuclear cardiology imaging is solidly based on many branches of science and engineering, including nuclear, optical, and mathematical physics; electrical and mechanical engineering; chemistry; and biology. This chapter uses principles from these scientific fields to provide an understanding of both the signals used and the imaging system that captures these signals. These principles have been simplified to fit the scope of this atlas.

Objective To estimate the heritability of myocardial blood flow (MBF) and coronary flow reserve (CFR) measured with positron emission tomography (PET). Design Cross-sectional twin study. Setting General clinical research centre of a university hospital at Atlanta, USA. Patients A sample of 180 middle-aged (mean±SD 55±2.9 years) male twins, including 107 monozygotic and 73 dizygotic twins. Main outcome measures All twins underwent imaging of MBF with PET 13 NH 3 at rest and after adenosine stress during a single imaging session. Structural equation modelling was used to estimate the heritability of MBF at rest and during adenosine stress, as well as of CFR. Results The basal MBF (mean±SD) was 0.69±0.20 ml/min/g, and the MBF during adenosine stress was 1.70±0.49 ml/min/g; the CFR was 2.62±0.99. There was substantial heritability for MBF both at rest (0.48, 95% CI 0.29 to 0.64) and during adenosine stress (0.51, 95% CI 0.29 to 0.68), as well as CFR (0.48, 95% CI 0.26 to 0.65). Conclusions For the first time, a substantial genetic contribution to the interindividual variation in MBF and CFR measured with PET in middle-aged men has been demonstrated. The data suggest that a fruitful direction for future work would be the identification of genetic variants for early atherosclerotic stages assessed by PET imaging.

Phase analysis has been developed and validated to measure left-ventricular dyssynchrony from gated SPECT myocardial perfusion imaging. The purpose of this study is to evaluate its performance in regions with perfusion defects.A special version of the eXtended CArdiac Torso digital phantom was developed to track B-spline points in each temporal frame. A region of 35 B-spline points in the inferior wall with normal and abnormal perfusion uptakes were simulated. Phase shifts were simulated in the same region, representing dyssynchronous contraction. Gated SPECT data were analyzed using a modified phase analysis algorithm, which tracked the same 35 B-spline points to calculate their phases.Phases and phase shifts measured in the B-spline points with perfusion uptake in the range of 50%-10% did not significantly differ from those measured in the same B-spline points with normal perfusion uptake.Phase analysis can accurately measure phases in regions with abnormal perfusion uptake as low as 10% of the perfusion uptake in the normal regions, which corresponded to a regional signal-to-noise ratio (SNR) of 12.0 or greater. In 42 consecutive patients with myocardial infarction20% of the left ventricle, only two patients had a SNR within the perfusion defects below that threshold.

We propose an improved region based segmentation model with shape priors that uses labels of confidence/interest to exclude the influence of certain regions in the image that may not provide useful information for segmentation. These could be regions in the image which are expected to have weak, missing or corrupt edges or they could be regions in the image which the user is not interested in segmenting, but are part of the object being segmented. In the training datasets, along with the manual segmentations we also generate an auxiliary map indicating these regions of low confidence/interest. Since, all the training images are acquired under similar conditions, we can train our algorithm to estimate these regions as well. Based on this training we will generate a map which indicates the regions in the image that are likely to contain no useful information for segmentation. We then use a parametric model to represent the segmenting curve as a combination of shape priors obtained by representing the training data as a collection of signed distance functions. We evolve an objective energy functional to evolve the global parameters that are used to represent the curve. We vary the influence each pixel has on the evolution of these parameters based on the confidence/interest label. When we use these labels to indicate the regions with low confidence; the regions containing accurate edges will have a dominant role in the evolution of the curve and the segmentation in the low confidence regions will be approximated based on the training data. Since our model evolves global parameters, it improves the segmentation even in the regions with accurate edges. This is because we eliminate the influence of the low confidence regions which may mislead the final segmentation. Similarly when we use the labels to indicate the regions which are not of importance, we will get a better segmentation of the object in the regions we are interested in.

Myocardial perfusion imaging (MPI) using nuclear cardiology techniques has been widely applied in clinical practice because of its well-documented value in the diagnosis and prognosis of coronary artery disease. Industry has developed innovative designs for dedicated cardiac SPECT cameras that constrain the entire detector area to imaging just the heart. New software that recovers image resolution and limits image noise has also been implemented. These SPECT innovations are resulting in shortened study times or reduced radiation doses to patients, promoting easier scheduling, higher patient satisfaction, and, importantly, higher image quality. This article describes these cardiocentric SPECT software and hardware innovations, which provide a strong foundation for the continued success of myocardial perfusion SPECT.

Explicit fusion of perfusion data from Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) with coronary artery anatomy from Computed Tomographic Coronary Angiography (CTCA) has been shown to improve the diagnostic yield for coronary artery disease (CAD) compared to either modality alone. However, most clinically available methods were developed for multimodal scanners or require interactive alignment prior to display and analysis. A new approach was developed to register and display the two distributions obtained either from a single multimodal imager or from separate scanners, and a preliminary validation was undertaken using interactive alignment by experts.

Multi-Harmonic Phase Analysis (MHPA) has been developed to quantify left-ventricular (LV) mechanical dyssynchrony with gated single photon emission tomography (SPECT) myocardial perfusion imaging (MPI). Although MHPA has shown promising clinical results, it needs to be optimized technically. The purpose of this study is to develop a tool to simulate LV mechanical dyssynchrony in gated SPECT MPI using an extended cardiac torso phantom (XCAT). A special version of the XCAT phantom was developed to control regional myocardial wall thickening using more than 300 B-splines points over the LV myocardium and 26 temporal frames over a cardiac cycle. By shifting the regional myocardial wall thickness values in the temporal domain, regional phase delays can be simulated to represent LV mechanical dyssynchrony. Gated SPECT data were created with phase delays of 0°, ±20°, ±40°, and ±60° in the anterior wall for a LV with normal perfusion. The activity maps given by XCAT were submitted to a SPECT simulator to generate gated SPECT projections. The gated SPECT projections were reconstructed and reoriented into gated short-axis images, which were then submitted to MHPA. A correlation of R2 = 0.9941 between MHPA measured and simulated regional phase delays was obtained, indicating that MHPA can accurately measure the simulated phase delays. Thus, a simulation tool based on the XCAT phantom has been developed to simulate regional phase delays, which can be accurately measured by MHPA. This tool can offer the opportunities to investigate the relationship between phase delay and myocardial defect, and to optimize MHPA for various factors such as noise and cardiac torsion in future studies.

Left ventricular (LV) wall thickening (WT) assessed from myocardial perfusion (MP) gated SPECT data has been reported to be a marker of functional recovery following myocardial damage. However, the accuracy of WT measurements obtained in the clinical setting rarely has been validated against an independent quantitative reference standard. The purpose of this investigation was to assess the degree to which quantified MP WT agrees with cardiac magnetic resonance (CMR) WT measurements, and to determine whether quantitation is as accurate as visual analysis in detecting abnormal regional WT. MP and ECG-gated True-FISP CMR data were analyzed for 20 patients evaluated after myocardial infarction (age 60 ± 11 years; 95% males). An experienced observer visually graded MP WT on a 5-point scale while viewing MP cines. MP WT was quantified using “Emory Cardiac Toolbox” (ECTb) algorithms. MP algorithms isolated myocardial counts and generated polar maps of WT. CMR data were analyzed by Medis “MASS” software. Manually drawn endocardial and epicardial contours were used to compute WT on CMR. CMR data also were processed for 10 age-matched normal volunteers to define the CMR WT threshold of abnormality. All computations were sampled into conventional 17 ACC/AHA LV wall segments. Receiver operating characteristics (ROC) curve analysis provided discrimination thresholds for optimal accuracy, which subsequently were used to dichotomize the MP methods. WT abnormalities also were assessed for the 3 major arterial territories, and for total numbers of abnormal segments per patient. 25% of all segments had abnormally low WT by CMR. While MP quantitation underestimated CMR WT values for segments with normal WT (26 ± 13% vs. 56 ± 28%, P

Background Major depressive disorder (MDD) is associated with coronary heart disease (CHD), but the mechanisms are unclear. The presence of MDD may increase CHD risk by affecting microvascular circulation. It is also plausible that genetic factors influencing MDD may overlap with those for CHD. We sought to examine the relationship between MDD and coronary flow reserve (CFR), the ratio of maximum flow during stress to flow at rest measured in milliliters per minute per gram of tissue. Methods We examined 289 male middle-aged twins, including 106 twins (53 twin pairs) discordant for a lifetime history of MDD and 183 control twins (unrelated to any twins in the experimental group) without MDD. To calculate CFR, we used positron emission tomography with nitrogen 13 ( 13 N) ammonia to evaluate myocardial blood flow at rest and after adenosine stress. A standard perfusion defect score was also used to assess myocardial ischemia. Results There was no difference in myocardial ischemia between twins with and without MDD. Among the dizygotic twin pairs discordant for MDD, the CFR was 14% lower in the twins with MDD than in their brothers without MDD (2.36 vs 2.74) ( P = .03). This association was not present in the monozygotic discordant pairs who were genetically matched (2.86 vs 2.64) ( P = .19). The zygosity-MDD interaction after adjustment was significant ( P = .006). The CFR in the dizygotic twins with MDD was also lower than in the control twins. Conclusions Our results provide evidence for a shared genetic pathway between MDD and microvascular dysfunction. Common pathophysiologic processes may link MDD and early atherosclerosis.

This article describes advancements in hardware and software for myocardial perfusion imaging that are becoming commercialized today and their implication in clinical practice.