A retrospective evaluation of Bayesian-penalized likelihood reconstruction for [15O]H2O myocardial perfusion imaging.

BACKGROUND: New Block-Sequential-Regularized-Expectation-Maximization (BSREM) image reconstruction technique has been introduced for clinical use mainly for oncologic use. Accurate and quantitative image reconstruction is essential in myocardial perfusion imaging with positron emission tomography (PET) as it utilizes absolute quantitation of myocardial blood flow (MBF). The aim of the study was to evaluate BSREM reconstruction for quantitation in patients with suspected coronary artery disease (CAD). METHODS AND RESULTS: We analyzed cardiac [15O]H2O PET studies of 177 patients evaluated for CAD. Differences between BSREM and Ordered-Subset-Expectation-Maximization with Time-Of-Flight (TOF) and Point-Spread-Function (PSF) modeling (OSEM-TOF-PSF) in terms of MBF, perfusable tissue fraction, and vascular volume fraction were measured. Classification of ischemia was assessed between the algorithms. OSEM-TOF-PSF and BSREM provided similar global stress MBF in patients with ischemia (1.84 ± 0.21 g⋅ml-1⋅min-1 vs 1.86 ± 0.21 g⋅ml-1⋅min-1) and no ischemia (3.26 ± 0.34 g⋅ml-1⋅min-1 vs 3.28 ± 0.34 g⋅ml-1⋅min-1). Global resting MBF was also similar (0.97 ± 0.12 g⋅ml-1⋅min-1 and 1.12 ± 0.06 g⋅ml-1⋅min-1). The largest mean relative difference in MBF values was 7%. Presence of myocardial ischemia was classified concordantly in 99% of patients using OSEM-TOF-PSF and BSREM reconstructions CONCLUSION: OSEM-TOF-PSF and BSREM image reconstructions produce similar MBF values and diagnosis of myocardial ischemia in patients undergoing [15O]H2O PET due to suspected obstructive coronary artery disease.

Assessment of MRI-Based Attenuation Correction for MRI-Only Radiotherapy Treatment Planning of the Brain.

Magnetic resonance imaging-only radiotherapy treatment planning (MRI-only RTP) and positron emission tomography (PET)-MRI imaging require generation of synthetic computed tomography (sCT) images from MRI images. In this study, initial dosimetric evaluation was performed for a previously developed MRI-based attenuation correction (MRAC) method for use in MRI-only RTP of the brain. MRAC-based sCT images were retrospectively generated from Dixon MR images of 20 patients who had previously received external beam radiation therapy (EBRT). Bone segmentation performance and Dice similarity coefficient of the sCT conversion method were evaluated for bone volumes on CT images. Dose calculation accuracy was assessed by recalculating the CT-based EBRT plans using the sCT images as the base attenuation data. Dose comparison was done for the sCT- and CT-based EBRT plans in planning target volume (PTV) and organs at risk (OAR). Parametric dose comparison showed mean relative differences of <0.4% for PTV and <1.0% for OARs. Mean gamma index pass rates of 95.7% with the 2%/2 mm agreement criterion and 96.5% with the 1%/1 mm agreement criterion were determined for glioma and metastasis patients, respectively. Based on the results, MRI-only RTP using sCT images generated from MRAC images can be a feasible alternative for radiotherapy of the brain.

CONTEMPORARY RADIATION DOSES IN INTERVENTIONAL CARDIOLOGY: A NATIONWIDE STUDY OF PATIENT SKIN DOSES IN FINLAND.

In contemporary interventional cardiology, for typical elderly patients, the most severe radiation-related harm to patients can be considered to come from skin exposures. In this paper, maximum local skin doses in cardiological procedures are explored with Gafchromic film dosimetry. Film and reader calibrations and reading were performed at the Secondary Standards Dosimetry Laboratory of the Radiation and Nuclear Safety Authority (STUK), and data were gathered from seven hospitals in Finland. As alert levels for early transient erythema, 200 Gycm2 kerma area product (KAP) and 2000 mGy air kerma levels for transcatheter aortic valve implantations (TAVI) procedures are proposed. The largest doses were measured in TAVI (4158.8 mGy) and percutaneous coronary interventions (PCI) (941.68 mGy). Accuracies of the GE DoseWatch and Siemens CareMonitor skin dose estimates were reasonable, but more results are needed to reliably assess and validate the tools' capabilities and reliabilities. Uncertainty of the Gafchromic dosimetry was estimated as 9.1% for a calibration with seven data points and 19.3% for a calibration with five data points.

A Computational Framework for Data Fusion in MEMS-Based Cardiac and Respiratory Gating.

Dual cardiac and respiratory gating is a well-known technique for motion compensation in nuclear medicine imaging. In this study, we present a new data fusion framework for dual cardiac and respiratory gating based on multidimensional microelectromechanical (MEMS) motion sensors. Our approach aims at robust estimation of the chest vibrations, that is, high-frequency precordial vibrations and low-frequency respiratory movements for prospective gating in positron emission tomography (PET), computed tomography (CT), and radiotherapy. Our sensing modality in the context of this paper is a single dual sensor unit, including accelerometer and gyroscope sensors to measure chest movements in three different orientations. Since accelerometer- and gyroscope-derived respiration signals represent the inclination of the chest, they are similar in morphology and have the same units. Therefore, we use principal component analysis (PCA) to combine them into a single signal. In contrast to this, the accelerometer- and gyroscope-derived cardiac signals correspond to the translational and rotational motions of the chest, and have different waveform characteristics and units. To combine these signals, we use independent component analysis (ICA) in order to obtain the underlying cardiac motion. From this cardiac motion signal, we obtain the systolic and diastolic phases of cardiac cycles by using an adaptive multi-scale peak detector and a short-time autocorrelation function. Three groups of subjects, including healthy controls (n = 7), healthy volunteers (n = 12), and patients with a history of coronary artery disease (n = 19) were studied to establish a quantitative framework for assessing the performance of the presented work in prospective imaging applications. The results of this investigation showed a fairly strong positive correlation (average r = 0.73 to 0.87) between the MEMS-derived (including corresponding PCA fusion) respiration curves and the reference optical camera and respiration belt sensors. Additionally, the mean time offset of MEMS-driven triggers from camera-driven triggers was 0.23 to 0.3 ± 0.15 to 0.17 s. For each cardiac cycle, the feature of the MEMS signals indicating a systolic time interval was identified, and its relation to the total cardiac cycle length was also reported. The findings of this study suggest that the combination of chest angular velocity and accelerations using ICA and PCA can help to develop a robust dual cardiac and respiratory gating solution using only MEMS sensors. Therefore, the methods presented in this paper should help improve predictions of the cardiac and respiratory quiescent phases, particularly with the clinical patients. This study lays the groundwork for future research into clinical PET/CT imaging based on dual inertial sensors.

CONTEMPORARY RADIATION DOSES IN INTERVENTIONAL CARDIOLOGY: A NATIONWIDE STUDY OF PATIENT DOSES IN FINLAND.

The amount of interventional procedures such as percutaneous coronary intervention (PCI), transcatheter aortic valve implantation (TAVI), pacemaker implantation (PI) and ablations has increased within the previous decade. Simultaneously, novel fluoroscopy mainframes enable lower radiation doses for patients and operators. Therefore, there is a need to update the existing diagnostic reference levels (DRLs) and propose new ones for common or recently introduced procedures. We sought to assess patient radiation doses in interventional cardiology in a large sample from seven hospitals across Finland between 2014 and 2016. Data were used to set updated national DRLs for coronary angiographies (kerma-air product (KAP) 30 Gycm2) and PCIs (KAP 75 cm2), and novel levels for PIs (KAP 3.5 Gycm2), atrial fibrillation ablation procedures (KAP 25 Gycm2) and TAVI (KAP 90 Gycm2). Tentative KAP values were set for implantations of cardiac resynchronization therapy devices (CRT, KAP 22 Gycm2), electrophysiological treatment of atrioventricular nodal re-entry tachycardia (6 Gycm2) and atrial flutter procedures (KAP 16 Gycm2). The values for TAVI and CRT device implantation are published for the first time on national level. Dose from image acquisition (cine) constitutes the major part of the total dose in coronary and atrial fibrillation ablation procedures. For TAVI, patient weight is a good predictor of patient dose.

Accuracy of echocardiographic area-length method in chronic myocardial infarction: comparison with cardiac CT in pigs.

BACKGROUND: We evaluated echocardiographic area-length methods to measure left ventricle (LV) volumes and ejection fraction (EF) in parasternal short axis views in comparison with cardiac computed tomography (CT) in pigs with chronic myocardial infarction (MI). METHODS: Male farm pigs with surgical occlusion of the left anterior descending coronary artery (n = 9) or sham operation (n = 5) had transthoracic echocardiography and cardiac-CT 3 months after surgery. We measured length of the LV in parasternal long axis view, and both systolic and diastolic LV areas in parasternal short axis views at the level of mitral valve, papillary muscles and apex. Volumes and EF of the LV were calculated using Simpson's method of discs (tri-plane area) or Cylinder-hemiellipsoid method (single plane area). RESULTS: The pigs with coronary occlusion had anterior MI scars and reduced EF (average EF 42 ± 10%) by CT. Measurements of LV volumes and EF were reproducible by echocardiography. Compared with CT, end-diastolic volume (EDV) measured by echocardiography showed good correlation and agreement using either Simpson's method (r = 0.90; mean difference -2, 95% CI -47 to 43 mL) or Cylinder-hemiellipsoid method (r = 0.94; mean difference 3, 95% CI -44 to 49 mL). Furthermore, End-systolic volume (ESV) measured by echocardiography showed also good correlation and agreement using either Simpson's method (r = 0.94; mean difference 12 ml, 95% CI: -16 to 40) or Cylinder-hemiellipsoid method (r = 0.97; mean difference:13 ml, 95% CI: -8 to 33). EF was underestimated using either Simpson's method (r = 0.78; mean difference -6, 95% CI -11 to 1%) or Cylinder-hemiellipsoid method (r = 0.74; mean difference -4, 95% CI-10 to 2%). CONCLUSION: Our results indicate that measurement of LV volumes may be accurate, but EF is underestimated using either three or single parasternal short axis planes by echocardiography in a large animal model of chronic MI.

Absorption, distribution and excretion of intravenously injected (68)Ge/ (68)Ga generator eluate in healthy rats, and estimation of human radiation dosimetry.

BACKGROUND: This study evaluated the absorption, distribution, and excretion of Gallium-68 ((68)Ga) radionuclide after a single intravenous (i.v.) injection of (68)Ge/(68)Ga generator eluate in healthy rats. Additionally, human radiation doses were estimated from the rat data. METHODS: Twenty-one female and 21 male Sprague-Dawley rats were i.v. injected with 47 ± 4 MBq of (68)Ge/(68)Ga generator eluate, and the radioactivity of excised organs was measured using a gamma counter at 5, 30, 60, 120, or 180 min afterwards (n = 3-7 for each time point). The radioactivity concentration and plasma pharmacokinetic parameters were calculated. Subsequently, the estimates for human radiation dosimetry were determined. Additionally, 4 female and 5 male rats were positron emission tomography (PET) imaged for in vivo visualization of biodistribution. RESULTS: (68)Ga radioactivity was cleared relatively slowly from blood circulation and excreted into the urine, with some retention in the liver and spleen. Notably, the (68)Ga radioactivity in female genital organs, i.e., the uterus and ovaries, was considerable higher compared with male genitals. Extrapolating from the female and male rat (68)Ga data, the estimated effective dose was 0.0308 mSv/MBq for a 57-kg woman and 0.0191 mSv/MBq for a 70-kg man. CONCLUSIONS: The estimated human radiation burden of the (68)Ge/(68)Ga generator eluate was slightly higher for females and similar for males as compared with somatostatin receptor ligands (68)Ga-DOTANOC, (68)Ga-DOTATOC, and (68)Ga-DOTATATE, which is probably due to the retention in the liver and spleen. Our results revealed some differences between female and male rat data, which, at least in part, may be explained by the small sample size.

A novel respiratory gating method for oncologic positron emission tomography based on bioimpedance approach.

OBJECTIVE: Respiratory motion causes loss of image quality and inaccuracy of quantification in oncologic positron emission tomography (PET) imaging. This study introduces a bioimpedance-based gating method for compensation of respiratory motion artefacts. METHODS: The bioimpedance-based respiratory gating method was studied parallel to a clinically used respiratory gating method [Real-time Position Management by Varian Medical Systems] in 4D PET/CT acquisition of 9 oncologic patients. The quantitative analysis consisted of the evaluation of tumour SUVpeak, SUVmax and volume. Additionally, target-to-background ratios as well as motion in cranial-caudal and anterior-posterior directions were measured. The evaluation was performed with amplitude- and time-based gating using averaged attenuation correction maps. RESULTS: Bioimpedance gating resulted in 17.7-18.9 % increase in mean SUVpeak and 20.0-21.4 % decrease in mean volume compared to non-gated images. The maximum motion measured from the bioimpedance-gated images was 19 mm in cranial-caudal direction and 9 mm in anterior-posterior direction. CONCLUSIONS: Bioimpedance-based respiratory gating compensates the adverse effects of motion in oncologic PET imaging.

Comparison of end-expiratory respiratory gating methods for PET/CT.

BACKGROUND: Respiratory motion in positron emission tomography/computed tomography (PET/CT) causes underestimation of standardized uptake value (SUV) and variation of lesion volume, while PET and CT attenuation correction (CTAC) mismatch may introduce artefacts. The aim was to compare end-expiratory gating methods of PET and CTAC. MATERIAL AND METHODS: Three methods named the minimum-constant, slope-based and amplitude-median were developed and evaluated on gating efficiency. Method evaluation and optimization was performed on 23 simulated and 23 recorded signals from a mixed patient group. The optimized methods were applied in PET/CT imaging of seven patients, consisting of non-gated CTAC, whole-body PET and four-dimensional (4D) PET/CT. Gating efficiency was evaluated by preservation of the respiratory signal, PET-CTAC alignment, image noise and measurement of lesion SUV maximum (SUVmax), SUV mean (SUVmean) and volume. The methods were evaluated with non-gated PET and end-expiratory phase of five-bin phase-gated PET. End-expiratory gated 4D-CTAC and averaged CTAC were compared for attenuation correction of end-expiratory gated PET. RESULTS: Mean fraction of data preserved was larger (23-34%) with end-expiratory gating compared to phase-gated PET. End-expiratory gating showed increased SUVmax (8.2-8.4 g/ml), SUVmean (5.7-5.8 g/ml) and decreased lesion volume (-11.3-16.8%) compared to non-gated PET (SUVmax 6.2 g/ml, SUVmean 4.7 g/ml) and phase-gated PET (SUVmax 8.0 g/ml, SUVmean 5.6 g/ml). Using averaged CTAC and end-expiratory 4D-CTAC produced similar results concerning SUVmax, with less than 5% difference. Additionally, CTAC-PET-mismatch was minimal when end-expiratory 4D-CTAC was used. CONCLUSION: End-expiratory gating in PET/CT results in SUVmax and SUVmean increase and reduced lesion volume compared to non-gated PET and phase-gated PET. End-expiratory 4D-CTAC or averaged CTAC will offer similar accuracy for attenuation correction of end-expiratory gated PET.

Comparative study with new accuracy metrics for target volume contouring in PET image guided radiation therapy.

The impact of PET on radiation therapy is held back by poor methods of defining functional volumes of interest. Many new software tools are being proposed for contouring target volumes but the different approaches are not adequately compared and their accuracy is poorly evaluated due to the illdefinition of ground truth. This paper compares the largest cohort to date of established, emerging and proposed PET contouring methods, in terms of accuracy and variability. We emphasise spatial accuracy and present a new metric that addresses the lack of unique ground truth. 30 methods are used at 13 different institutions to contour functional VOIs in clinical PET/CT and a custom-built PET phantom representing typical problems in image guided radiotherapy. Contouring methods are grouped according to algorithmic type, level of interactivity and how they exploit structural information in hybrid images. Experiments reveal benefits of high levels of user interaction, as well as simultaneous visualisation of CT images and PET gradients to guide interactive procedures. Method-wise evaluation identifies the danger of over-automation and the value of prior knowledge built into an algorithm.

Evaluation of 68Ga-labeled tracers for PET imaging of myocardial perfusion in pigs.

PURPOSE: We evaluated four potential gallium-68 (68Ga)-labeled tracers for positron emission tomography (PET) imaging of myocardial perfusion in comparison with oxygen-15-labeled water ([15O]water) in healthy pigs. Four hexadentate salicylaldimine ligands derived from bis(3-aminopropyl)ethylenediamine (BAPEN) that showed promise in previous rat experiments were selected for this study. METHODS: Following an evaluation of myocardial blood flow with [15O]water PET, the pigs (total n=14) underwent a dynamic 90-min PET study with one of four 68Ga-labeled BAPEN derivatives (n=3-5 per tracer) either at rest or under adenosine stress. Serial arterial blood samples were collected during the imaging for the measurements of total radioactivity, radiometabolites, plasma protein binding and blood-to-plasma ratio for the 68Ga chelates. Time-activity curves of the left ventricular blood pool and myocardium were derived from PET images, and metabolite-corrected arterial input function was used for kinetic modeling. Also, ex vivo biodistribution of 68Ga radioactivity was analyzed. RESULTS: All four 68Ga tracers showed undesirably slow myocardial accumulation over time, but their in vivo stability, clearance from blood and the kinetics of the myocardium uptake varied. [68Ga][Ga-(sal)2BAPDMEN]1+ showed the highest myocardial uptake in PET images and tissue samples (myocardium-to-blood ratio 7.63±1.89, myocardium-to-lung ratio 3.03±0.33 and myocardium-to-liver ratio 1.80±0.82). However, there was no correlation between the myocardial perfusion measured with [15O]water and the net uptake rates or K1 values of the 68Ga chelates. CONCLUSION: Our results revealed that myocardial accumulation of the 68Ga chelates proposed for myocardial perfusion imaging with PET was slow and not determined by myocardial perfusion in a large animal model. These findings suggest that the studied tracers are not suitable for clinical imaging of myocardial perfusion.

Cross-validation of input functions obtained by H2 15O PET imaging of rat heart and a blood flow-through detector.

PURPOSE: Positron emission tomography (PET) with ¹5O-labeled water (H2 ¹5O) facilitates the visualization and quantification of blood flow in clinical investigations and also in small animals. The quantification of blood flow requires an input function, which is generally obtained by measuring radioactivity in arterial blood withdrawn during PET scanning. However, this approach is not always feasible, because abundant blood sampling may affect the physiological process being measured. The purpose of the present study was to develop and cross-validate two methods, namely, a blood- and an image-based method for obtaining the input function for blood flow studies from rat H2 ¹5O PET. METHODS: The study material consisted of two separate groups of rats. Group 1 rats were imaged twice by a high-resolution research tomograph PET camera at resting condition for a test-retest study (n = 4), and group 2 rats were imaged with and without adenosine infusion for a rest-stress study (n = 4). In group 1, radioactivity concentration in arterial blood was measured with a new flow-through detector during imaging and a blood-based input function was obtained. The image-based input function was estimated using time-activity curves from the left ventricle and myocardial regions. To validate the two input function methods, myocardial blood flow (MBF) and cerebral blood flow (CBF) were computed, and the methods were tested for reproducibility (test-retest study) and changes (rest-stress study). RESULTS: The blood- and image-based input functions were similar, and the corresponding CBF values differed only by -6.9 ± 8.1%. In the test-retest study, both MBF and CBF showed good reproducibility, and in the rest-stress study, adenosine significantly increased both MBF (P = 0.035) and CBF (P = 0.029), compared with the resting condition. CONCLUSION: It is possible both to measure the input function from rat arteria femoralis during H2 ¹5O PET imaging and to estimate the input function from rat H2 ¹5O PET images, thereby facilitating the assessment of blood flow in organs visible in PET images.

No effects of short-term GSM mobile phone radiation on cerebral blood flow measured using positron emission tomography.

The present study investigated the effects of 902.4 MHz global system for mobile communications (GSM) mobile phone radiation on cerebral blood flow using positron emission tomography (PET) with the (15) O-water tracer. Fifteen young, healthy, right-handed male subjects were exposed to phone radiation from three different locations (left ear, right ear, forehead) and to sham exposure to test for possible exposure effects on brain regions close to the exposure source. Whole-brain [¹5O]H2O-PET images were acquired 12 times, 3 for each condition, in a counterbalanced order. Subjects were exposed for 5 min in each scan while performing a simple visual vigilance task. Temperature was also measured in the head region (forehead, eyes, cheeks, ear canals) during exposure. The exposure induced a slight temperature rise in the ear canals but did not affect brain hemodynamics and task performance. The results provided no evidence for acute effects of short-term mobile phone radiation on cerebral blood flow.

Clinical value of absolute quantification of myocardial perfusion with (15)O-water in coronary artery disease.

BACKGROUND: The standard interpretation of perfusion imaging is based on the assessment of relative perfusion distribution. The limitations of that approach have been recognized in patients with multivessel disease and endothelial dysfunction. To date, however, no large clinical studies have investigated the value of measuring quantitative blood flow and compared that with relative uptake. METHODS AND RESULTS: One hundred four patients with moderate (30%-70%) pretest likelihood of coronary artery disease (CAD) underwent PET imaging during adenosine stress using (15)O-water and dynamic imaging. Absolute myocardial blood flow was calculated from which both standard relative myocardial perfusion images and images scaled to a known absolute scale were produced. The patients and the regions then were classified as normal or abnormal and compared against the reference of conventional angiography with fractional flow reserve. In patient-based analysis, the positive predictive value, negative predictive value, and accuracy of absolute perfusion in the detection of any obstructive CAD were 86%, 97%, and 92%, respectively, with absolute quantification. The corresponding values with relative analysis were 61%, 83%, and 73%, respectively. In region-based analysis, the receiver operating characteristic curves confirmed that the absolute quantification was superior to relative assessment. In particular, the specificity and positive predictive value were low using just relative differences in flow. Only 9 of 24 patients with 3-vessel disease were correctly assessed using relative analysis. CONCLUSIONS: The measurement of myocardial blood flow in absolute terms has a significant impact on the interpretation of myocardial perfusion. As expected, multivessel disease is more accurately detected.

GSM mobile phone radiation suppresses brain glucose metabolism.

We investigated the effects of mobile phone radiation on cerebral glucose metabolism using high-resolution positron emission tomography (PET) with the (18)F-deoxyglucose (FDG) tracer. A long half-life (109 minutes) of the (18)F isotope allowed a long, natural exposure condition outside the PET scanner. Thirteen young right-handed male subjects were exposed to a pulse-modulated 902.4 MHz Global System for Mobile Communications signal for 33 minutes, while performing a simple visual vigilance task. Temperature was also measured in the head region (forehead, eyes, cheeks, ear canals) during exposure. (18)F-deoxyglucose PET images acquired after the exposure showed that relative cerebral metabolic rate of glucose was significantly reduced in the temporoparietal junction and anterior temporal lobe of the right hemisphere ipsilateral to the exposure. Temperature rise was also observed on the exposed side of the head, but the magnitude was very small. The exposure did not affect task performance (reaction time, error rate). Our results show that short-term mobile phone exposure can locally suppress brain energy metabolism in humans.

Intrapericardial, but not extrapericardial, fat is an independent predictor of impaired hyperemic coronary perfusion in coronary artery disease.

OBJECTIVE: To measure intrapericardial fat (IPF), extrapericardial fat (EPF), and myocardial perfusion (MBF) in patients with and without coronary artery disease (CAD), hypothesizing that perfusion is more strongly associated with IPF because it is in direct anatomic contiguity with the myocardium or coronary arteries. METHODS AND RESULTS: Fat surrounding the heart may increase the risk of CAD and calcification, but little is known about the role of MBF in this relationship. The study included 107 patients with an intermediate likelihood of CAD. Positron emission tomography/computed tomography was used to measure IPF and EPF volumes and coronary artery calcium level, together with MBF at rest and during adenosine-induced hyperemia. Subsequently, all subjects underwent coronary angiography and were grouped for presence/absence of CAD and severity of myocardial hypoperfusion. IPF and EPF levels were higher in men and in patients with CAD (n=85) than in those without CAD (n=22) (P<0.001). EPF was increased regardless of the degree of stenoses (n=45), whereas IPF was selectively increased in subjects with obstructive stenoses (n=40). IPF and EPF levels were both associated with coronary artery calcium scores (R=0.25 and R=0.26, respectively; P<0.02), coronary flow reserve (R=-0.37 and R=-0.38, respectively; P<0.001), and hyperemic MBF (R=-0.36 and R=-0.44, respectively; P<0.0005). Male sex was a strong negative predictor of MBF. After discounting for confounders, myocardial hyperemic perfusion was predicted independently by sex, coronary artery calcium score, and IPF, but not EPF. CONCLUSIONS: CAD is accompanied by augmented fat depots surrounding the heart, which are negatively related to coronary flow hyperemia. Among fat depots, IPF was the only independent predictor of hyperemic MBF, supporting the hypothesis of a direct paracrine/vasocrine effect.

Comparison of 2D and 3D performance for FDG PET with different acquisition times in oncological patients.

OBJECTIVE: Collecting positron emission tomography data in three-dimensional (3D) mode may potentially allow reduction of the tracer dose and/or the acquisition time without compromising image quality thereby making the procedure more patient-friendly and cost effective. The objective of our study was to compare VUE Point iterative reconstruction algorithm in positron emission tomography data obtained in 3D and two-dimensional (2D) mode in routine clinical diagnostic setting in oncological patients. METHODS: Standard whole-body imaging (33 patients) was followed by rescanning of the target region in 2D and 3D mode. The ListMode data were histogrammed to 4, 3 and 2 min frames. Visual and semiquantitative analyses were performed. Effects of tumour volume and body mass index on tissue visualisation were evaluated. RESULTS: Visual image quality in 3D mode was superior to 2D. Maximum and mean standardised uptake values of tumours did not differ between 2D and 3D. Mean background standardised uptake values were significantly lower in 3D compared with 2D. 3D tumour to background ratios were higher than 2D in small lesions and obese patients (body mass index > or = 30) with all acquisition times. CONCLUSION: The new reconstruction method produces images of similar or better quality with 3D compared with 2D mode. The difference is pronounced in small lesions and in obese patients. According to our study, 3D is the preferred acquisition mode for routine whole-body evaluation of oncological patients.

Motion detection and correction for dynamic ( 15)O-water myocardial perfusion PET studies.

PURPOSE: Patient motion during dynamic PET studies is a well-documented source of errors. The purpose of this study was to investigate the incidence of frame-to-frame motion in dynamic ( 15)O-water myocardial perfusion PET studies, to test the efficacy of motion correction methods and to study whether implementation of motion correction would have an impact on the perfusion results. METHODS: We developed a motion detection procedure using external radioactive skin markers and frame-to-frame alignment. To evaluate motion, marker coordinates inside the field of view were determined in each frame for each study. The highest number of frames with identical spatial coordinates during the study were defined as "non-moved". Movement was considered present if even one marker changed position, by one pixel/frame compared with reference, in one axis, and such frames were defined as "moved". We tested manual, in-house-developed motion correction software and an automatic motion correction using a rigid body point model implemented in MIPAV (Medical Image Processing, Analysis and Visualisation) software. After motion correction, remaining motion was re-analysed. Myocardial blood flow (MBF) values were calculated for both non-corrected and motion-corrected datasets. RESULTS: At rest, patient motion was found in 18% of the frames, but during pharmacological stress the fraction increased to 45% and during physical exercise it rose to 80%. Both motion correction algorithms significantly decreased (p<0.006) the number of moved frames and the amplitude of motion (p<0.04). Motion correction significantly increased MBF results during bicycle exercise (p<0.02). At rest or during adenosine infusion, the motion correction had no significant effects on MBF values. CONCLUSION: Significant motion is a common phenomenon in dynamic cardiac studies during adenosine infusion but especially during exercise. Applying motion correction for the data acquired during exercise clearly changed the MBF results, indicating that motion correction is required for these studies.