Assessment of cardiac wall motion and ejection fraction with gated PET using N-13 ammonia

BACKGROUND: Cardiac gating is not routinely used in cardiac positron emission tomography (PET). The aim of this study was to determine the feasibility of assessing regional wall motion, ejection fraction (EF), cardiac volumes, and mass with nitrogen-13 ammonia (N-13 ammonia) at the time of PET myocardial perfusion imaging. METHODS: We studied 12 healthy volunteers (mean age, 28 +/- 8 years) and 53 patients with documented coronary artery disease (CAD) (mean age, 59 +/- 11 years). All subjects received a single administration of approximately 600 MBq (16 mCi) of N-13 ammonia intravenously. A 6-minute dynamic scan was performed for quantitative assessment of myocardial perfusion at rest, followed by a separate, 13-minute static scan acquired in the gated mode (8 equal bins). Gated data was imported into the Emory Toolbox. Wall motion was evaluated by dividing the myocardium into 9 anatomic regions graded semiquantitatively. RESULTS: Healthy volunteers had a normal EF (61 +/- 6), end systolic volume (ESV) (37 +/- 15 mL), end diastolic volume (EDV) (89 +/- 25 mL), and cardiac mass (116 +/- 18 g). In contrast, patients with CAD showed reduced EF (32 +/- 13%) and increased ESV (129 +/- 56 mL), EDV (188 +/- 68 mL), and cardiac mass (173 +/- 45 g) (P < 0.001 for each). In patients with CAD, EF measured by gated PET correlated significantly to independent measurements of EF (P < 0.001). CONCLUSIONS: Gating of cardiac perfusion images obtained after administration of N-13 ammonia is feasible and appears to be an accurate means of evaluating regional and global cardiac function. Gating can provide important additional diagnostic and prognostic information.     

Quantitative assessment of wall motion in gated SPECT using the centerline method

Evaluation of myocardial wall motion is an important assessment of heart function. Specific analysis programs in nuclear medicine, such as QGS (quantitative gated SPECT) analysis and p-FAST (perfusion-function assessment for myocardial SPECT), have been used to assess wall motion, but they have not evaluated it through a comparison of normal data. The centerline method, using left ventriculograms (LVG), evaluates regional wall motion quantitatively through a comparison of normal data and patient data, and abnormality of wall motion is expressed in units of standard deviation (SD) s from the mean motion in a reference population. However, angiography is an invasive inspection, wall motion analysis is usually in one direction, and the conventional centerline method is not a three-dimensional analysis. The purpose of this study was to apply the centerline method to nuclear medicine and examine the wall motion of subjects through a comparison of normal wall motion non-invasively and in a three-dimensional way. We arranged the analysis program using C language and inspected it using a dynamic cardiac phantom and computed tomography (CT) scanner. We made a polar map that indicated the mean and SD of normal wall motion. Our proposed method was able to assess the wall motion of subjects quantitatively through a comparison of normal wall motion in nuclear medicine.     

Importance of gated CT acquisition for the quantitative improvement of the gated PET/CT in moving phantom

Objective

The aim of this study was to investigate the utility of gated PET/CT and CT attenuation correction (AC) for the quantitation of radioactivity.

Methods

An ellipse phantom containing six spheres, ranging from 10 to 37 mm in diameter, was filled with 36.7 kBq/mL of F-18. The respiratory motion was simulated by a motor-driven plastic platform to move the phantom with a displacement of 2 cm in the craniocaudal direction at a frequency of 15/min. With the phantom at rest, PET/CT data were acquired and used as a standard (nonmotion). With the phantom in motion, PET data were acquired in both the static and gated modes (sPET and gPET, respectively). Helical CT (HCT), slow CT (SCT), average CT (ACT), and four-dimensional CT (4DCT) were acquired and used to correct attenuation. On both PET and CT images, the maximum radioactivity, dimensions, and CT numbers were measured on the central slices.

Results

In nonmotion, recovery coefficients whose spheres were 22 mm or smaller gradually decreased. Regarding motion, the PET counts of the spheres in the static acquisition were lower than those acquired in nonmotion with either type of CTAC (sPET–HCT: ?43.8%, sPET–SCT: ?51.4%, sPET–ACT: ?49.5%). Gated acquisition of PET significantly improved the PET counts (gPET–HCT: ?30.1%) (p < 0.05), while additional gated acquisition of CT significantly improved them further (gPET–4DCT: ?15.2%) (p < 0.01). The dimensions of sPET were overestimated, but those of gPET were close to the standard values. The SCT significantly overestimated the dimensions, and the water density area decreased (p < 0.01). The 4DCT images were similar to the HCT images.

Conclusions

In respiratory motion, PET acquisition in the static mode underestimated the radioactivity and overestimated the dimensions. Neither SCT nor ACT improved these errors. Although PET acquisition in the gated mode improved the quantification of PET/CT images, the additional gated CT acquisition using 4DCT is required for further improvement.     

FDG imaging of lung nodules: a phantom study comparing SPECT, camera-based PET, and dedicated PET

PURPOSE: To evaluate 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) imaging of simulated lung nodules in a realistic chest phantom by using attenuation-corrected and non-attenuation-corrected 511-keV single photon emission computed tomography (SPECT), camera-based positron emission tomography (PET), and dedicated PET imaging. MATERIALS AND METHODS: Spheres with diameters of 6, 10, 13, and 22 mm were placed in the lungs of an anthropomorphic chest phantom to simulate nodules. The lungs, nodules, chest wall, and mediastinum were filled with fluorine-18 activities based on the average radionuclide concentrations in those structures from analysis of attenuation-corrected dedicated FDG PET scans. The image sets were evaluated visually and quantitatively by using contrast and signal-to-noise ratios. RESULTS: Attenuation correction reduced the artificially high apparent uptake in the lungs, restored the spherical shape to the nodules, and provided an accurate outer body contour with appropriate intensity. Dedicated PET depicted all four nodules, camera-based PET depicted the three largest nodules, and SPECT depicted the two largest nodules. Lesion contrast was better on the attenuation-corrected images than on the non-attenuation-corrected images. The signal-to-noise ratio generally was improved with attenuation correction. CONCLUSION: Attenuation correction results in many changes in the images and improves lesion detection.     

PET performance measurements using the NEMA NU 2-2001 standard.

The NU 2-1994 standard document for PET performance measurements has recently been updated. The updated document, NU 2-2001, includes revised measurements for spatial resolution, intrinsic scatter fraction, sensitivity, counting rate performance, and accuracy of count loss and randoms corrections. The revised measurements are designed to allow testing of dedicated PET systems in both 2-dimensional and 3-dimensional modes as well as coincidence gamma cameras, conditions not considered in the original NU 2-1994 standard. In addition, the updated measurements strive toward being more representative of clinical studies, in particular, whole-body imaging. METHODS: Performance measurements following the NU 2-1994 and NU 2-2001 standards were performed on several different PET scanners. Differences between the procedures and resulting performance characteristics, as well as the rationale for these changes, were noted. RESULTS: Spatial resolution is measured with a point source in all 3 directions, rather than a line source, as specified previously. For the measurements of intrinsic scatter fraction, sensitivity, and counting rate performance, a 70-cm line source is now specified, instead of a 19-cm-long cylindric phantom. The longer configuration permits measurement of these performance characteristics over the entire axial field of view of all current PET scanners and incorporates the effects of activity outside the scanner. A measurement of image quality has been added in an effort to measure overall image quality under clinically realistic conditions. This measurement replaces the individual measurements of uniformity and of the accuracy of corrections for attenuation and scatter. CONCLUSION: The changes from the NU 2-1994 standard to the NU 2-2001 standard strive toward establishing relevance with clinical studies. The tests in the updated standard also are, in general, simpler and less time-consuming to perform than those in the NU 2-1994 standard.     

应用自行研制的运动模体研究呼吸状态改变对立体定向门控放疗的影响

目的 评价患者呼吸状态的改变对实时位置监测系统(RPM)引导下自由呼吸立体定向门控放疗影响。方法 通过自行研制运动模体模拟患者治疗过程中出现基线偏移,呼吸频率改变,呼气末延时、吸气末延时,以及不规则呼吸情况,并分析三维适形、固定野动态调强、单弧旋转调强3组计划各状态变化与模体中心小球位置(L)及电离室受照剂量的相关性。结果 自研模体的摆位重复性和测量稳定性良好。L与基线偏移呈现正相关(r=0.99,P＜0.01)。基线偏移小于摆位误差时,剂量变化在4%以内,相对较小,超出后受照剂量快速下降并呈现负相关(r= -0.95,P＜0.01),偏移超出与不超出摆位误差时所测得的受照剂量,差异具有统计学意义(Z= -3.06,P<0.01)。3组计划受基线偏移的影响率差异无统计学意义(P>0.05)。呼吸频率改变对 L 和剂量影响较小。吸气末延迟和呼气末延迟都导致3组计划剂量下降,最大达-1.74%,同时吸气末延迟相对呼气末延迟影响更大,差异具有统计学意义(Z= -2.67,P<0.01),但延迟时间长短对剂量的影响率没有明显相关性(P＞0.05),3组计划受波形改变的影响率差异无统计学意义(P＞0.05)。不规则呼吸对剂量影响较大,3组计划重复测量6次受照剂量分别为三维适形(709.68±180.00)cGy;固定野动态调强(751.40±127.16)cGy;单弧旋转调强(750.00±185.60)cGy,均小于处方剂量,一致性欠佳。结论 患者呼吸状态改变会导致剂量下降,基线偏移超出摆位误差阈值或者波形变异较大出现不规则呼吸时更甚,且与放疗技术不相关。     

Dual gated PET/CT imaging of small targets of the heart: Method description and testing with a dynamic heart phantom

Background  

In PET imaging respiratory and cardiac contraction motions interfere the imaging of heart. The aim was to develop and evaluate dual gating method for improving the detection of small targets of the heart.     

Validation of gated blood-pool SPECT cardiac measurements tested using a biventricular dynamic physical phantom.

We have developed a biventricular dynamic physical cardiac phantom to test gated blood-pool (GBP) SPECT image-processing algorithms. Such phantoms provide absolute values against which to assess accuracy of both right and left computed ventricular volume and ejection fraction (EF) measurements. METHODS: Two silicon-rubber chambers driven by 2 piston pumps simulated crescent-shaped right ventricles wrapped partway around ellopsoid left ventricles. Twenty experiments were performed at Ghent University, for which right and left ventricular true volume and EF ranges were 65-275 mL and 55-165 mL and 7%-49% and 12%-69%, respectively. Resulting 64 x 64 simulated GBP SPECT images acquired at 16 frames per R-R interval were sent to Columbia University, where 2 observers analyzed images independently of each other, without knowledge of true values. Algorithms automatically segmented right ventricular activity volumetrically from left ventricular activity. Automated valve planes, midventricular planes, and segmentation regions were presented to observers, who accepted these choices or modified them as necessary. One observer repeated measurements >1 mo later without reference to previous determinations. RESULTS: Linear correlation coefficients (r) of the mean of the 3 GBP SPECT observations versus true values for right and left ventricles were 0.80 and 0.94 for EF and 0.94 and 0.95 for volumes, respectively. Correlations for right and left ventricles were 0.97 and 0.97 for EF and 0.96 and 0.89 for volumes, respectively, for interobserver agreement and 0.97 and 0.98 for EF and 0.96 and 0.90 for volumes, respectively, for intraobserver agreement. No trends were detected, though volumes and right ventricular EFs were significantly higher than true values. CONCLUSION: Overall, GBP SPECT measurements correlated strongly with true values. The phantom evaluated shows considerable promise for helping to guide algorithm developments for improved GBP SPECT accuracy.     

Discovery ST PET性能测试与NEMA标准的应用

目的通过对1台 Discovery ST PET 的验收,探讨2001年版美国国家电气制造商协会(NEMA)标准的实际应用。方法使用 NEMA 标准的测试模型和测试方法,对 PET 空间分辨率、散射系数(SF,%)、计数丢失、随机测试和灵敏度进行测试。结果空间分辨率[半高宽(FWHM),mm]横向为6.12/6.37[二维/三维(2D/3D)],轴向为5.18/5.44(2D/3D);SF 为19.71(2D)和44.36(3D);系统灵敏度(计数·s~(-1)·kBq~(-1)):模型置有效视野中心位置为2.17/10.26(2D/3D),模型偏移至有效视野中心半径10cm 处为2.23/10.57(2D/3D)。结论厂家必须提供配套的 NEMA 测试模型和测试软件。该 PET/CT 仪的 PET 部分所测试指标达到出厂要求。     

Reduction of respiratory motion artifacts in PET imaging of lung cancer by respiratory correlated dynamic PET: methodology and comparison with respiratory gated PET.

This study proposes a new method to reduce respiratory motion artifacts in PET images of lung cancer. The method is referred to as respiratory-correlated dynamic PET (RCDPET). RCDPET enables the acquisition of 4-dimensional PET data without the need for a respiratory tracking device. In this article, we compare this method with respiratory-gated PET (RGPET). Both methods provide the ability to correct for motion artifacts and more accurately quantitate radiotracer uptake within lung lesions. Both methods were evaluated in phantom studies and 1 patient. METHODS: With RCDPET, data are acquired in consecutive 1-s time frames. A point source attached to a rigid foam block is set on the patient's abdomen and is extended into the camera field of view at the level of the lesion by means of a low-density rod. The position of this source is used to track respiratory motion through the consecutive dynamic frames. Image frames corresponding to a user-selected lesion position within the breathing cycle, in correlation with the point source position, are then identified after scanning. The sinograms of the selected image frames are summed and then reconstructed using iterative reconstruction with segmented attenuation correction. RESULTS: The results from phantom studies with both RGPET and RCDPET were within 10% agreement, for both activity quantitation and image noise levels. In a clinical application, the quantitation of the SUV(max) and the lesion's size showed a 6% and 2% difference, respectively, between RCDPET and RGPET measurements. CONCLUSION: RCDPET can be considered as a comparable, or alternative, method to RGPET in reducing the smearing effects due to respiration and improving quantitation of PET in the thorax. One advantage of RCDPET over RGPET is the ability to retrospectively reconstruct the PET data at any phase or amplitude in the breathing cycle.     

Detection of intracavitary masses on gated scans: a phantom study

A series of 1.5, 2.0 and 3.0 cm diameter paraffin balls were placed on a 3 cm tether within a simulated left ventricular balloon phantom to determine the maximal balloon volume that permitted identification of the lesion. When images were recorded with the phantom stationary, the lesions could be detected at 100, 280 and 360 ml volumes, respectively. When the phantom was set in motion with a fixed 80 ml stroke volume, the lesions were detected at 120, 320 and 360 ml, respectively. These findings suggest that gating does not decrease lesion detection even when the lesion is freely mobile, and a 1.5 cm lesion would be difficult to detect in an enlarged ventricle, but 2 and 3 cm lesions could be detected even in the presence of moderate ventricular enlargement.     

Incidental myocardial infarct on conventional nongated CT: a review of the spectrum of findings with gated CT and cardiac MRI correlation

OBJECTIVE: Myocardial infarctions (MIs) are frequently evident on routine chest or abdominal CT, even when studies are not performed for cardiac-specific indications. However, the telltale signs of an MI may be easily overlooked. Herein, we present the spectrum of appearances of MIs, including areas of fat attenuation, myocardial calcifications, focal areas of wall thinning or aneurysm formation, and perfusion abnormalities. Thrombi, especially when present at the apex of the left ventricle, may also suggest an MI. CONCLUSION: The increased use of CT in the evaluation of patients for a variety of indications gives the radiologist the unique opportunity to recognize findings consistent with MI in patients who may not have a prior diagnosis of ischemic heart disease.     

Quantitative gated PET for the assessment of left ventricular function in small animals.

18F-FDG PET can identify areas of myocardial viability and necrosis and provide useful information on the effectiveness of experimental techniques designed to improve contractile function and myocardial vascularization in small animals. The left ventricular volume (LVV) and left ventricular ejection fraction (LVEF) in normal and diseased rats were measured in vivo using the high-resolution avalanche photodiode (APD) small-animal PET scanner of the Université de Sherbrooke. The measurements obtained by PET were compared with those obtained by high-resolution echocardiography and with known values obtained from a small, variable-volume cardiac phantom. METHODS: List-mode gated (18)F-FDG PET studies were performed using the APD PET scanner on 30 rats: 11 healthy, 4 under septic shock, and 15 with heart failure induced by ligature of the left coronary artery. PET images were resized to match human-scale pixels and analyzed using a standard clinical cardiac software program. The LVV and LVEF from the same animals were also evaluated by echocardiography. RESULTS: Agreement was excellent between the endocardial volumes determined by PET and the actual volumes of the cardiac phantom (r(2) = 0.96). Agreement between PET and echocardiography for LVV ranged from good in healthy rats (r(2) = 0.89) to fair in diseased rats (r(2) = 0.49). Agreement was fair between LVEF values measured by the 2 methods (r(2) = 0.56). Normal rats had an average LVEF of 83.2% +/- 8.0% using PET and 81.6% +/- 6.0% using echocardiography. In rats with heart failure, LVEF was 54.6% +/- 15.9% using PET and 54.2% +/- 13.3% using echocardiography. CONCLUSION: Both PET and echocardiography clearly differentiated normal rats from rats with heart failure. Echocardiography is fast and convenient, whereas list-mode PET is also able to assess defect size, myocardial viability, and metabolism.     

Quantitative analysis of regional wall motion and thickening by quantitative gated SPECT: comparison with visual analysis

PURPOSE: Electrocardiograph-gated myocardial SPECT permits a quantitative assessment of global and regional functions by quantitative gated SPECT software. To validate quantitative indexes of wall motion and wall thickening, the authors compared these indexes with visual scores. MATERIALS AND METHODS: Gated myocardial SPECT was performed 60 minutes after the administration of Tc-99m sestamibi at rest in 42 patients with coronary artery disease. Regional wall motion (measured in millimeters and wall thickening (expressed as a percentage) were calculated by quantitative gated SPECT software in nine left ventricular myocardial segments and the results were compared with the five-point visual score interpretations of cinematic display. RESULTS: A high correlation of wall motion was observed between the quantitative and visual analyses (r = 0.810; P < 0.001). In addition, a high but somewhat less significant correlation of wall thickening was observed between the quantitative and visual analyses (r = 0.606; P < 0.001). CONCLUSIONS: In conclusion, regional wall motion and wall thickening can be evaluated quantitatively by electrocardiograph-gated myocardial SPECT and quantitative gated SPECT software. This will be useful for functional assessments made with various interventions.     

Metallic artifacts caused by dental metal prostheses on PET images: a PET/CT phantom study using different PET/CT scanners

Objective  The objective of this study was to investigate the effects of computed tomography (CT) artifacts caused by dental metal prostheses on positron emission tomography (PET) images. Methods  A dental arch cast was fixed in a cylindrical water-bath phantom. A spherical phantom positioned in the vicinity of the dental arch cast was used to simulate a tumor. To simulate the tumor imaging, the ratio of the ¹⁸F-fluoro-deoxy-glucose radioactivity concentration of the spherical phantom to that of the water-bath phantom was set at 2.5. A dental bridge composed of a gold–silver–palladium alloy on the right mandibular side was prepared. A spherical phantom was set in the white artifact area on the CT images (site A), in a slightly remote area from the white artifact (site B), and in a black artifact area (site C). A PET/CT scan was performed with and without the metal bridge at each simulated tumor site, and the artifactual influence was evaluated on the axial attenuation-corrected (AC) PET images, in which the simulated tumor produced the strongest accumulation. Measurements were performed using three types of PET/CT scanners (scanners 1 and 2 with CT-based attenuation correction, and 3 with Cesium-137 (¹³⁷Cs)-based attenuation correction). The influence of the metal bridge was evaluated using the change rate of the SUVmean with and without the metal bridge. Results  At site A, an overestimation was shown (scanner 1: +5.0% and scanner 2: +2.5%), while scanner 3 showed an underestimation of −31.8%. At site B, an overestimation was shown (scanner 1: +2.1% and scanner 2: +2.0%), while scanner 3 showed an underestimation of −2.6%. However, at site C, an underestimation was shown (scanner 1: −25.0%, scanner 2: −32.4%, and scanner 3: −8.4%). Conclusions  When CT is used for attenuation correction in patients with dental metal prostheses, an underestimation of radioactivity of accumulated tracer is anticipated in the dark streak artifact area on the CT images. In this study, the dark streak artifacts of the CT caused by metallic dental prostheses may cause false negative finding of PET/CT in detecting small and/or low uptake tumor in the oral cavity.     

Quantitative analysis of left-ventricular function using gated single photon emission tomography

We describe a quantitative method that measures segmental motion of the left ventricle, using tomographic slices obtained by gated single photon emission tomography (GSPECT). These slices contain the major axis of the left ventricle and are presumed to show wall motion directed towards a center of contraction. Values of parameters describing segmental wall motion in GSPECT were obtained from 61 patients, who received a left cardiac catheterization 1 hr later. These values were compared with results of similar calculations applied to data from contrast ventriculography. We conclude that GSPECT allows a detailed and quantitative, noninvasive study of wall motion of all left ventricular segments, with high inter- and intraobserver reproducibility.     

Performance characteristics of a newly developed PET/CT scanner using NEMA standards in 2D and 3D modes.

This study evaluates the 2-dimensional (2D) and 3-dimensional (3D) performance characteristics of a newly developed PET/CT scanner using the National Electrical Manufacturers Association (NEMA) NU 2-1994 (NU94) and NEMA NU 2-2001 (NU01) standards. The PET detector array consists of 10,080 individual bismuth germanate crystals arranged in 24 rings of 420 crystals each. The size of each crystal is 6.3 x 6.3 x 30 mm in the axial, transaxial, and radial dimensions, respectively. The PET detector ring diameter is 88.6 cm with axial and transaxial fields of view (FOVs) of 15.7 and 70 cm, respectively. The scanner has a uniform patient port of 70 cm throughout the PET and CT FOV, and the PET scanner is equipped with retractable septa to allow 2D and 3D imaging. METHODS: Spatial resolution, scatter fraction, sensitivity, counting rate, image quality, and accuracy as defined by the NEMA protocols of NU94 and NU01 for 2D and 3D modes are evaluated. The 2D mode data were acquired with a maximum ring difference of 5, whereas the 3D mode acquisition used ring differences of 23. Both 2D and 3D mode data were acquired with an energy window of 375-650 keV. Random estimation from singles counting rate was applied to all relevant analysis. In addition, images from 2 clinical whole-body oncology studies acquired in 2D and 3D modes are shown to demonstrate the image quality obtained from this scanner. RESULTS: The 2D NU94 transaxial resolution is 6.1-mm full width at half maximum (FWHM) 1 cm off center and increases to 6.9 mm tangential and 8.1 mm radial at a radius (R) of 20 cm. NU01 2D average transaxial (axial) FWHM resolution measured 6.1 (5.2) mm at R = 1 cm and 6.7 (6.1) mm at R = 10 cm. The NU94 scatter fraction for 2D (3D) was 13% (29%), whereas the NU01 scatter fraction gave 19% (45%). NU01 peak 2D (3D) noise equivalent counting rate (T(2)/[T + R + S]) was 90.2 (67.8) kilocount per second (kcps) at 52.5 (12) kBq/mL. Total 2D (3D) system sensitivity for true events is 8 (32.9) kcps/kBq/mL for NU94 and 1.95 (9.2) kcps/Bq for NU01. CONCLUSION: The results show excellent system sensitivity with relatively uniform resolution throughout the FOV, making this scanner highly suitable for whole-body studies.     

Assessment of the influence of atrial fibrillation on gated SPECT perfusion data by comparison with simultaneously acquired nongated SPECT data

The impact of arrhythmias on the evaluation of perfusion data from myocardial gated SPECT has been assessed by comparing arrhythmic patients with nonarrhythmic patients or by simulating rhythm disturbances. Whether gating-related artifacts may have a clinically relevant influence on the evaluation of perfusion in atrial fibrillation (AF) patients is still uncertain. Recently, collection of nongated and gated datasets during the same SPECT acquisition has become possible. The aim of this study was to examine the difference in myocardial perfusion between simultaneously acquired gated and nongated SPECT data in AF patients. METHODS: In 44 consecutive AF patients who underwent myocardial perfusion SPECT for standard clinical indications, both a gated and a nongated study were simultaneously acquired. Perfusion was estimated in a masked manner on a 20-segment model using an established scoring scheme. RESULTS: Agreement was good between the gated and nongated perfusion scores on a segment basis; the agreement for resting scores was the highest, with those for stress and difference scores being lower (Spearman rho = 0.82, 0.74, and 0.55, respectively). On a patient basis, a similar trend was seen in summed resting scores (rho = 0.911), summed stress scores (rho = 0.779), and summed difference scores (rho = 0.596). When summed stress and summed difference data were grouped by severity class (normal, mild abnormality, moderate abnormality, and severe abnormality), agreement decreased from rho = 0.818, kappa = 0.639, for summed stress score to rho = 0.549, kappa = 0.367, for summed difference score. The severity class of inducible ischemia changed in 17 patients (39%) if a (summed) gated image was used instead of a standard nongated perfusion image. CONCLUSION: AF may have a clinically relevant impact on summed gated perfusion images, compared with images simultaneously obtained without gating in the same patients. Therefore, acquisition of a nongated SPECT study is mandatory for accurate assessment of myocardial perfusion in AF patients.