Cardiac PET Imaging Research Articles

Attenuation correction in cardiac PET/CT with three different CT protocols: a comparison with conventional PET

CT-based attenuation correction may influence cardiac PET owing to its higher susceptibility to misalignment compared with conventional (68)Ge transmission scans. The aims of this study were to evaluate whether CT attenuation correction leads to changes in tracer distribution compared with conventional cardiac PET and to determine a suitable CT protocol. A total of 27 patients underwent PET/CT and subsequently a PET scan. Twenty patients received a low-dose CT (LDCT group; 120 kV, 26 mA, 8-s scan time), seven patients a slow CT (SCT group; 120 kV, 99 mA, 46-s scan time) and ten patients an ultra-low-dose CT (ULDCT group; 80 kV, 13 mA, 5-s scan time) as the transmission scan in PET/CT. Polar maps were divided into 17 segments and regression analysis was computed in every scan pair (CT attenuation corrected-(68)Ge attenuation corrected). Correlation coefficient (r), the slope (s) and the offset (os) of the regression line were determined. Visual assessment of misalignment between the transmission and emission data was performed. The effective dose of the different transmission scans was calculated. Overall, there was a moderate correlation between the mean values measured in all segments on PET/CT and on PET when using LDCT (r=0.78, p<0.0001), SCT (r=0.79, p<0.0001) and ULDCT (r=0.82, p<0.0001). No differences were observed when comparing the scores assigned in the visual misalignment assessment in the three groups (p=0.12). The differences between the results from the regression analysis observed in the respective groups were not statistically significant (Kruskal-Wallis p=0.11 for r, p=0.67 for s and p=0.27 for os). The effective dose was lowest for the ULDCT. Our study shows that CT-based attenuation correction is feasible for cardiac PET imaging. The results indicate that ultra-low-dose CT is the preferable choice for transmission scanning.

Imaging Markers of Adverse Remodeling: from Organ to Organelle

The identification of quantifiable noninvasive imaging markers of remodeling is critical for diagnosis, prognosis, and outcome assessment. To date, a number of structural and functional measures have been used to quantify adverse remodeling, but these markers are incomplete, providing little information about the activity of the underlying processes. The development of new markers of adverse remodeling representing changes on a histopathologic, cellular, molecular, and neurohormonal level promise to expand our understanding of adverse remodeling, providing a more complete picture of the process. Particularly exciting are emerging molecular imaging techniques incorporating the use of targeted and activatable molecular probes with the modalities of cardiac MRI, SPECT, PET, and optical imaging.

Rigid-body transformation of list-mode projection data for respiratory motion correction in cardiac PET

High-resolution cardiac PET imaging with emphasis on quantification would benefit from eliminating the problem of respiratory movement during data acquisition. Respiratory gating on the basis of list-mode data has been employed previously as one approach to reduce motion effects. However, it results in poor count statistics with degradation of image quality. This work reports on the implementation of a technique to correct for respiratory motion in the area of the heart at no extra cost for count statistics and with the potential to maintain ECG gating, based on rigid-body transformations on list-mode data event-by-event. A motion-corrected data set is obtained by assigning, after pre-correction for detector efficiency and photon attenuation, individual lines-of-response to new detector pairs with consideration of respiratory motion. Parameters of respiratory motion are obtained from a series of gated image sets by means of image registration. Respiration is recorded simultaneously with the list-mode data using an inductive respiration monitor with an elasticized belt at chest level. The accuracy of the technique was assessed with point-source data showing a good correlation between measured and true transformations. The technique was applied on phantom data with simulated respiratory motion, showing successful recovery of tracer distribution and contrast on the motion-corrected images, and on patient data with C15O and 18FDG. Quantitative assessment of preliminary C15O patient data showed improvement in the recovery coefficient at the centre of the left ventricle.

34.17 Validation of a rapid transmission scan and Bayesian reconstruction algorithm in dedicated cardiac PET imaging

34.17 Validation of a rapid transmission scan and Bayesian reconstruction algorithm in dedicated cardiac PET imaging

Cardiac PET imaging in mice with simultaneous cardiac and respiratory gating

Gating firmware and software were developed for the microPET II small animal scanner. The measured cardiac and respiratory signals were collected and converted to TTL gating signals by a Biopac MP150 data acquisition system and sent to microPET II through two BNC connectors on the front panel. During acquisition, the coincidence monitor takes the average of the last eight gate input cycles and inserts this into the list mode data stream on the falling edge of the gating pulse. This value is then used to determine the current time interval of the next gate cycle when the list mode data are sorted into sinograms. The gating firmware and software were validated by an experiment using a rotating point source. Mouse heart (18F-FDG) and bone (18F−) imaging was performed with simultaneous cardiac and respiratory gating. It was clearly demonstrated that the contractile function of the mouse heart can be studied by cardiac-gated imaging with microPET II. The left ventricular volumes at different times of the cardiac cycle were measured and the ejection fraction was calculated. In the bone scan, no detectable movement caused by heart contraction was observed. Respiratory motion was more subtle with virtually no motion for more than 75% of the respiratory cycle. The motion of the mouse heart and bones in the thorax caused by respiration was less than 1 mm. It appears with the current resolution of PET, and the small fraction of the respiratory cycle in which motion occurs, that respiratory gating is probably not necessary for most mouse cardiac studies.

America’s Children

The rising tide of overweight and obesity in this nation and indeed around the world is apparent to all. From airlines to clothing manufacturers, industry has responded, either by charging larger customers more money for the space they occupy or by providing more accommodating sizes. Even the “final” industry has acquiesced—Goliath Casket, Inc, of Lynn, Ind, now provides several lines of oversize resting places for people weighing up to 700 lb, for whom conventional caskets are much too small. Of course, the tragedy is that these caskets are holding many who die too young. Obesity has been recognized as a major determinant of atherosclerotic cardiovascular disease since 1998,1 but our efforts to stem the tide in the United States have not been successful. The Centers for Disease Control and Prevention (CDC) have documented an increasing prevalence of this disorder during the period from 1985 to 2003 via the Behavioral Risk Factor Surveillance System,2 with increasing rates of overweight and obesity documented in successive surveys. Most recently, data from the National Center for Health Statistics National Health and Nutrition Examination Survey, which uses actual body measurements,3 showed that although US adult men and women are ≈1 in taller than they were in 1960, they are nearly 25 lb heavier on average as well. The average body mass index (BMI) has increased in adults from ≈25 in 1960 to 28 in 2002. Most troublesome were the data in children. A 10-year-old boy in 1963 weighed on average 74.2 lb. In 2002, he weighed nearly 85 lb. Fifteen-year-old boys were ≈15 lb heavier in 2002, and 15-year-old girls were ≈12 pounds heavier. Although children’s heights also increased (except for those of 15-year-old girls), the increase was not proportional; our children are a little taller, but they are much heavier. Finally, …

Accuracy of cardiac PET imaging using post-injection transmission scan

The purpose of this study was to investigate the accuracy of cardiac PET with post-injection transmission scans. We performed a phantom study using 18F solution as well as 13N-ammonia PET study of ten patients. The average activities of no myocardial defect phantom model were estimated, and myocardial defect sizes of 12 phantom models were measured by pre- and post-injection transmission methods at various 18F activities. In 13N-ammonia PET at rest and during adenosine triphosphate (ATP) stress studies, measured defect sizes were compared between both methods. The ratios of average activity estimated by both methods (post/pre value) were almost 1.00 at each 18F activity and segment. Measured defect sizes by both methods showed an excellent correlation with true defect sizes (r = 0.98, p < 0.01 for pre vs. true value: r = 0.98, p < 0.01 for post vs. true value). The mean absolute errors of measurements were minimal up to 3.5% LV, and were similar between both methods. In 13N-ammonia PET, measured defect sizes by both methods also showed a good correlation (r = 0.97, p < 0.01). The results indicate that cardiac PET imaging with post-injection transmission scan provides information on myocardial tracer activity as well as myocardial defect size as does conventional pre-injection transmission method.

The effect of glucose load on both cardiac and skeletal muscle FDG uptake

Background: The augmentation of the myocardial FDG uptake after a glucose load is very well established. However, the response of the skeletal muscle to the same glucose load has not been clearly demonstrated. The aim of this study is to demonstrate an increased skeletal muscle FDG uptake after a standard oral glucose load. To this end, we compared myocardial and skeletal muscle FDG uptake in a group of fasted patients to that of a second group of patients who underwent FDG PET scanning following oral glucose load. Methods: We included 41 patients (20 Male, 21 Female; age:26–72 years) without any cardiac pathology who had whole body FDG PET scan after several hours of fasting (4–24) in the first group. In the second group, we included 9 patients (8M; 1F; age 52–80 years) who had cardiac FDG PET imaging following a 50 g of oral glucose load. PET images were acquired with a Phillips Allegro scanner. We calculated the standard uptake values (SUV= Cts/injected dose/pt weight) of myocardium, arterial blood and skeletal muscle for both groups using regions of interest over the left ventricular myocardium, left ventricular cavity and skeletal muscle. Statistical analysis was performed using unpaired t test. Results: The results for both groups are given in table below. * Groups Heart SUV * Blood SUV Muscle SUV * Heart/Blood * Heart/Muscle Gp1 (n = 41) 4.8 ± 3.07 1.9 ± 0.64 0.88 ± 0.29 5.78 ± 3.70 2.54 ± 1.17 Gp2 (n = 9) 8.9 ± 5.25 2.39 ± 0.83 1.52 ± 0.50 6.62 ± 5.24 3.72 ± 1.70 * p < 0.05 There were statistically significant difference (p<0.05) between p values for heart and skeletal muscle uptake and for the heart to blood ratio. Conclusions: Both myocardial and skeletal muscle FDG uptake were higher in patients that received glucose load. However, the arterial concentration was similar. Skeletal muscle uptake could be used as an indicator of fasting status in patients undergoing FDG PET imaging.

Cardiac PET imaging of blood flow, metabolism, and function in normal and infarcted rats

The rat heart is an excellent model for the investigation of cardiac physiology and metabolism. It has been used extensively for ex vivo studies of the normal heart as well as for the study of various heart diseases. With the advent of dedicated high-resolution small animal PET scanners, it is now possible to transpose many of the cardiac investigations routinely used in humans to the rat. These include the in vivo measurement of myocardial blood flow, metabolism, and function. Because these techniques are non-invasive, the same animal can be imaged repetitively, thus allowing for follow-up studies of disease progression and for the monitoring of new therapeutic methods. In this work, we report on cardiac studies performed in normal and diseased rats using the Sherbrooke avalanche photodiode PET scanner, a small animal PET imaging device achieving 14 /spl mu/l volumetric spatial resolution with excellent image signal-to-noise ratio. The system also features flexible list-mode data acquisition, which allows dynamic studies to be resampled as desired for kinetic modeling. Examples of the application of cardiac PET imaging to the follow-up of infarcted rats treated with experimental revascularisation therapy will be presented.

Simplification of analysis procedures in inter-subject studies with cardiac PET imaging

Quantitative analysis in positron emission tomography imaging usually necessitates several studies carried out under the same protocol in order to get functional or metabolic parameter values with low variations. Apart from subject preparation and measurements in similar conditions, the data analysis should be done as uniformly as possible. In this work we report PET data obtained in normal and ischemic rats, measured with 13N-ammonia and 11C-acetate to extract myocardial blood flow and oxygen consumption, and analysed with the usual region of interest (ROI) drawing method in each rat individually, in comparison to a new method based on resampling all the rat heart images to a common model, then the ROIs are drawn once and copied onto each rat image sequence.

Phantom Studies Investigating Extravascular Density Imaging for Partial Volume Correction of 3-D PET&amp;lt;tex&amp;gt;$^18$&amp;lt;/tex&amp;gt;FDG Studies

Limited scanner resolution and cardiac motion contribute to partial volume (PV) averaging of cardiac PET images. An extravascular (EV) density image, created from the subtraction of a blood pool scan from a transmission image, has been used to correct for PV averaging in H/sub 2//sup 15/O studies using 2-D imaging but not with 3-D imaging of other tracers such as /sup 18/FDG. A cardiac phantom emulating the left ventricle was used to characterize the method for use in 3-D PET studies. Measurement of the average myocardial activity showed PV losses of 32% below the true activity (p<0.001). Initial application of the EV density correction still yielded a myocardial activity 13% below the true value (p<0.001). This failure of the EV density image was due to the 1.66 mm thick plastic barrier separating the myocardial and ventricular chambers within the phantom. Upon removal of this artifact by morphological dilation of the blood pool, the corrected myocardial value was within 2% of the true value (p=ns). Spherical ROIs (diameter of 2 to 10 mm), evenly distributed about the myocardium, were also used to calculate the average activity. The EV density image was able to account for PV averaging throughout the range of diameters to within a 5% accuracy, however, a small bias was seen as the size of the ROIs increased. This indicated a slight mismatch between the emission and transmission image resolutions, a result of the difference in data acquisitions (i.e., span and ring difference) and default smoothing. These results show that the use of EV density image to correct for PV averaging is possible with 3-D PET. A method of correcting barrier effects in phantoms has been presented, as well as a process for evaluating resolution mismatch.

The need for standardisation of cardiac FDG PET imaging in the evaluation of myocardial viability in patients with chronic ischaemic left ventricular dysfunction.

The evaluation of myocardial glucose utilisation with fluorine-18 fluorodeoxyglucose (FDG) and positron emission tomography is currently considered the most reliable tool for the identification of myocardial viability. However, the investigations using FDG imaging to predict improvement in left ventricular (LV) function after revascularisation have reported wide ranges for sensitivity (71%-100%) and, in particular, for specificity (33%-91%). The variable results may be related to differences in study populations but also to differences in the imaging protocols employed. Detailed analysis of the published studies has revealed differences in study populations, patient selection criteria, the methods for assessing changes in LV function post revascularisation and the timing of these assessments. Even more importantly, protocols have varied substantially with regard to imaging equipment, perfusion tracers, metabolic conditions, data analysis and interpretation of results. In addition, evaluation of patients with insulin resistance appears to represent a specific challenge. This review examines the different study protocols and methodologies used for myocardial FDG imaging in order to draw conclusions concerning optimal imaging protocols. It appears that the optimisation and standardisation of study protocols and analysis of FDG images for the assessment of myocardial viability are critical. In addition, multi-centre trials seem warranted on prediction of long-term function, congestive heart failure symptoms, survival and quality of life.

Gated rubidium-82 cardiac PET imaging: evaluation of left ventricular wall motion

Gated rubidium-82 cardiac PET imaging: evaluation of left ventricular wall motion

18.2 Model-based analysis of gated cardiac PET images to assess left-ventricular volume and contractile function

18.2 Model-based analysis of gated cardiac PET images to assess left-ventricular volume and contractile function

The effect of contraction and twist on myocardial PET and SPECT image resolution: a mathematical phantom study

Motion of the heart blurs cardiac PET and SPECT images. A mathematical phantom was constructed that models the contractile and non-uniform twisting motions of the left ventricular myocardium as the heart beats. The phantom was used to estimate the effect of normal heart motion on ECT image resolution and quantitation in regions of interest (ROIs). The movement of mid-myocardial points was tracked, from which motion blurring was computed. Clinical PET resolution of 7 mm was degraded to 10-12 mm FWHM in the direction of motion and clinical SPECT resolution of 14 mm to 15-16 mm FWHM. Contractile motion was greater near the base and twisting motion was greater near the apex. The blur due to both motions was equivalent to 7-10 mm FWHM Gaussian smoothing in the direction of motion. Activity weight coefficients characterized how activity in source model ROIs contributed to activity in short and long axis ROIs. The effect of contraction was dependent on whether the ROIs were from short or long axis slices and on the ROI location. The activity weights for short axis slices showed the effect of twist in blurring activity to adjacent angular sectors. This effect was not seen for constant thickness long axis slices because the angular range of the slices was greater, particularly near the apex. The contrast of perfusion defects in short axis ROIs was decreased by cardiac twist. A mathematical heart phantom that models contractile and twisting motions is useful for investigating the effect of these motions on cardiac ECT studies.

Synthesis of two optically active calcium channel antagonists labelled with carbon-11 for in vivo cardiac PET imaging

(±)-S11568 ( 1. 3-ethyl-5-methyl-(±)-2-[(2-(2-aminoethoxy)ethoxy)methyl]-4-(2,3-dichlorophenyl)-6-methyl-1,4-dihydropyridine-3,5- dicarboxylate), has an in vitro profile of high potency and of high electivity for the low-voltage dependent L-type calcium channel. In in vitro binding studies, it displaced specifically bound (-)-[ 3H]PN 200–110 (isradipine ( 2), the reference molecule for in vitro studies) from cardiac and vascular smooth muscle preparations with potencies of 5.6 and 51 nM, respectively. It also appears as a pure pharmacological antagonist acting at a single channel L-type and free of any interaction at the benzothiazepine binding site such as amlodipine ( 3). Both enantiomers of S11568 have in vitro activities, the dextro isomer S12967 ((+)- 1) being 6 to 18-fold less potent than the levo one S12968 ((-)- 1). Two couples of optically active labelling precursors of S11568, ((-)- 10/(+)- 10 and (-)- 14/(+)- 14) have been synthesized using a modified Hantzsch's dihydropyridine synthesis. In both cases, the enantiomers were separated by preparative chiral HPLC. They both have been independently labelled with carbon-11, using [ 11C]diazomethane or [ 11C]iodomethane to give multimilliCurie quantities of (-)- 1 (S12968) and (+)- 1 (S12967) with high specific activities (500–1000 mCi/μmol, 18.5–37.0 GBq/μmol). Both enantiomers appear suitable for PET experiments: their myocardial concentration increases after a bolus injection to reach a maximum in 2 min and then remains on a plateau with a slight downslope while the blood concentration falls rapidly. Myocardial uptake was threefold higher than lung uptake, leading to a good contrast on PET images. The present preliminary biological results obtained in Beagle dogs showed that both enantiomers have similar myocardial kinetics and in vivo affinity for the left ventricular myocardium.

474. 心筋PET像における部分容積効果の検討

474. 心筋PET像における部分容積効果の検討

A new axial smoothing method based on elastic mapping

New PET scanners have higher axial and in-plane spatial resolutions but at the expense of reduced per plane sensitivity, which prevents the higher to be fully realized. Normally, Gaussian weighted interplane axial smoothing is used to reduce noise. In this study, the authors developed a new algorithm to first elastically map from adjacent planes to an expected plane location, then by simple averaging with the measured image at the corresponding axial plane location to reduce the image noise level. Compared with those images obtained by conventional axial-directional smoothing method, the images of the new method which are based on matching image features of adjacent planes have improved signal-to-noise ratio. To quantify the observation, both simulated cardiac images and real cardiac PET images were studied. The in-plane loss was measured by the effective global Gaussian resolution and the noise reduction was evaluated by the cross-correlation coefficient. Various Hanning reconstruction filters with cutoff frequency=0.5, 0.7, 1.0/spl times/Nyquist frequency and Ramp 1.0 filter were tested on simulated images. Results showed that the new method was robust to various noise levels and indicated larger noise reduction or better image feature preservation than by the conventional method.

Measurement of arterial tracer concentrations from cardiac PET images.

Cardiac PET imaging offers the potential capability for the noninvasive measurement of arterial input function. This capability is somewhat limited, however, because of partial volume and spillover effects. The purpose of this study was to validate arterial tracer concentration measurements using PET images by assigning a region of interest (ROI) to the left ventricle, left atrium (LA), and ascending aorta. We selected [11C]CO and [13N]ammonia as tracers, because the activity of [11C]CO is primarily in the blood pool and that of [13N]ammonia primarily in myocardial tissue. Six [11C]CO and 11 [13N]ammonia PET scans were obtained in 17 subjects. Arterial tracer concentrations determined by PET were compared with those measured by well counting of arterial blood sampling obtained at the midpoint of each image acquisition. Arterial tracer concentrations as determined by LA-PET imaging correlated closely with those measured by blood sampling (r = 0.996, slope = 1.00 for [11C]CO; r = 0.841, slope = 0.974 for [13N]ammonia). Partial volume and spillover effects were minimized by assigning an ROI to the LA. Arterial tracer concentrations can be measured noninvasively with cardiac PET.

Cardiac positron emission tomography

Cardiac PET studies may have a role in the early detection of coronary artery disease. The early prediction of the ultimate fate of reperfused myocardium with cardiac PET imaging remains elusive. At present the predominant clinical use of PET scans lies in the identification of ischemic but viable tissue. Cardiac PET imaging with a combination of perfusion and metabolic tracers can distinguish those patients with a history of previous infarctions and severe heart failure who will benefit from therapeutic revascularization. Conversely, the group that is not expected to improve will be spared needless and risky attempts at revascularization and will become candidates for cardiac transplantation at an earlier stage.