Dual-Gated Motion-Frozen Cardiac PET with Flurpiridaz F 18.

UNLABELLED: A novel PET radiotracer, Flurpiridaz F 18, has undergone phase II clinical trial evaluation as a high-resolution PET cardiac perfusion imaging agent. In a subgroup of patients imaged with this agent, we assessed the feasibility and benefit of simultaneous correction of respiratory and cardiac motion. METHODS: In 16 patients, PET imaging was performed on a 4-ring scanner in dual cardiac and respiratory gating mode. Four sets of data were reconstructed with high-definition reconstruction (HD•PET): ungated and 8-bin electrocardiography-gated images using 5-min acquisition, optimal respiratory gating (ORG)-as developed for oncologic imaging-using a narrow range of breathing amplitude around end-expiration level with 35% of the counts in a 7-min acquisition, and 4-bin respiration-gated and 8-bin electrocardiography-gated images (32 bins in total) using the 7-min acquisition (dual-gating, using all data). Motion-frozen (MF) registration algorithms were applied to electrocardiography-gated and dual-gated data, creating cardiac-MF and dual-MF images. We computed wall thickness, wall/cavity contrast, and contrast-to-noise ratio for standard, ORG, cardiac-MF, and dual-MF images to assess image quality. RESULTS: The wall/cavity contrast was similar for ungated (9.3 ± 2.9) and ORG (9.5 ± 3.2) images and improved for cardiac-MF (10.8 ± 3.6) and dual-MF images (14.8 ± 8.0) (P < 0.05). The contrast-to-noise ratio was 22.2 ± 9.1 with ungated, 24.7 ± 12.2 with ORG, 35.5 ± 12.8 with cardiac-MF, and 42.1 ± 13.2 with dual-MF images (all P < 0.05). The wall thickness was significantly decreased (P < 0.05) with dual-MF (11.6 ± 1.9 mm) compared with ungated (13.9 ± 2.8 mm), ORG (13.1 ± 2.9 mm), and cardiac-MF images (12.1 ± 2.7 mm). CONCLUSION: Dual (respiratory/cardiac)-gated perfusion imaging with Flurpiridaz F 18 is feasible and improves image resolution, contrast, and contrast-to-noise ratio when MF registration methods are applied.

Coronary arterial 18F-FDG uptake by fusion of PET and coronary CT angiography at sites of percutaneous stenting for acute myocardial infarction and stable coronary artery disease.

UNLABELLED: Whether (18)F-FDG PET can detect inflammation in the coronary arteries remains controversial. We examined (18)F-FDG uptake at the culprit sites of acute myocardial infarction (AMI) after percutaneous coronary stenting (PCS) by coregistering PET and coronary CT angiography (CTA). METHODS: Twenty nondiabetic patients with AMI (median age, 62 y; 16 men and 4 women) and 7 nondiabetic patients with stable coronary artery disease (CAD; median age, 67 y; 4 men and 3 women) underwent (18)F-FDG PET and coronary CTA 1-6 d after PCS of culprit stenoses. After a low-carbohydrate dietary preparation and more than 12 h of fasting, 480 MBq of (18)F-FDG were injected, and PET images were acquired 3 h later. Helical CTA was performed on a dual-source scanner. Stent position on attenuation-correction noncontrast CT and CTA was used to fuse PET and CTA. Two experienced readers masked to patient data independently quantified maximum target-to-background ratio (maxTBR) at each PCS site. A maxTBR greater than 2.0 was the criterion for significant uptake. RESULTS: Compared with stable CAD patients, more AMI patients exhibited a PCS site maxTBR greater than 2.0 (12/20 vs. 1/7, P = 0.04). More AMI patients were active smokers (9/20 vs. 0/7 in stable CAD, P = 0.03). After adjusting for baseline demographic differences, stent-myocardium distance, and myocardial (18)F-FDG uptake, presentation of AMI was positively associated with a PCS site maxTBR greater than 2.0 (odds ratio, 31.6; P = 0.044). Prevalence of excess myocardial (18)F-FDG uptake was similar in both populations (8/20 AMI vs. 3/7 stable CAD, P = 0.89). CONCLUSION: Systematic fusion of (18)F-FDG PET and coronary CTA demonstrated increased culprit site (18)F-FDG uptake more commonly in patients with AMI than in patients with stable CAD. However, this approach failed to detect increased signal at the culprit site in nearly half of AMI patients, highlighting the challenging nature of in vivo coronary artery plaque metabolic imaging. Nonetheless, our findings suggest that imaging of coronary artery inflammation is feasible, and further work evaluating (18)F-FDG uptake in high-risk coronary plaques prior to rupture would be of great interest.

Comparison of clinical tools for measurements of regional stress and rest myocardial blood flow assessed with 13N-ammonia PET/CT.

UNLABELLED: Several models for the quantitative analysis of myocardial blood flow (MBF) at stress and rest and myocardial flow reserve (MFR) with (13)N-ammonia myocardial perfusion PET have been implemented for clinical use. We aimed to compare quantitative results obtained from 3 software tools (QPET, syngo MBF, and PMOD), which perform PET MBF quantification with either a 2-compartment model (QPET and syngo MBF) or a 1-compartment model (PMOD). METHODS: We considered 33 adenosine stress and rest (13)N-ammonia studies (22 men and 11 women). Average age was 54.5 ± 15 y, and average body mass index was 26 ± 4.2. Eighteen patients had a very low likelihood of disease, with no chest pain, normal relative perfusion results, and normal function. All data were obtained on a PET/CT scanner in list mode with CT attenuation maps. Sixteen dynamic frames were reconstructed (twelve 10-s, two 30-s, one 1-min, and one 6-min frames). Global and regional stress and rest MBF and MFR values were obtained with each tool. Left ventricular contours and input function region were obtained automatically in system QPET and syngo MBF and manually in PMOD. RESULTS: The flow values and MFR values were highly correlated among the 3 packages (R(2) ranging from 0.88 to 0.92 for global values and from 0.78 to 0.94 for regional values. Mean reference MFR values were similar for QPET, syngo MBF, and PMOD (3.39 ± 1.22, 3.41 ± 0.76, and 3.66 ± 1.19, respectively) by 1-way ANOVA (P = 0.74). The lowest MFR in very low likelihood patients in any given vascular territory was 2.25 for QPET, 2.13 for syngo MBF, and 2.23 for PMOD. CONCLUSION: Different implementations of 1- and 2-compartment models demonstrate an excellent correlation in MFR for each vascular territory, with similar mean MFR values.

Automated quantitative Rb-82 3D PET/CT myocardial perfusion imaging: normal limits and correlation with invasive coronary angiography.

BACKGROUND: We aimed to characterize normal limits and to determine the diagnostic accuracy for an automated quantification of 3D 82-Rubidium (Rb-82) PET/CT myocardial perfusion imaging (MPI). METHODS: We studied 125 consecutive patients undergoing Rb-82 PET/CT MPI, including patients with suspected coronary artery disease (CAD) and invasive coronary angiography, and 42 patients with a low likelihood (LLk) of CAD. Normal limits for perfusion and function were derived from LLk patients. QPET software was used to quantify perfusion abnormality at rest and stress expressed as total perfusion deficit (TPD). RESULTS: Relative perfusion databases did not differ in any of the 17 segments between males and females. The areas under the receiver operating characteristic curve for detection of CAD were 0.86 for identification of ≥50% and ≥70% stenosis. The sensitivity/specificity was 86%/86% for detecting ≥50% stenosis and 93%/77% for ≥70% stenosis, respectively. In regard to normal limits, mean rest and stress left ventricular ejection fraction (LVEF) were 67% ± 10% and 75% ± 9%, respectively. Mean transient ischemic dilation ratio was 1.06 ± 0.14 and mean increase in LVEF with stress was 7.4% ± 6.1% (95th percentile of 0%). CONCLUSION: Normal limits have been established for 3D Rb-82 PET/CT analysis with QPET software. Fully automated quantification of myocardial perfusion PET data shows high diagnostic accuracy for detecting obstructive CAD.

Automatic 3D registration of dynamic stress and rest (82)Rb and flurpiridaz F 18 myocardial perfusion PET data for patient motion detection and correction.

PURPOSE: The authors aimed to develop an image-based registration scheme to detect and correct patient motion in stress and rest cardiac positron emission tomography (PET)/CT images. The patient motion correction was of primary interest and the effects of patient motion with the use of flurpiridaz F 18 and (82)Rb were demonstrated. METHODS: The authors evaluated stress/rest PET myocardial perfusion imaging datasets in 30 patients (60 datasets in total, 21 male and 9 female) using a new perfusion agent (flurpiridaz F 18) (n = 16) and (82)Rb (n = 14), acquired on a Siemens Biograph-64 scanner in list mode. Stress and rest images were reconstructed into 4 ((82)Rb) or 10 (flurpiridaz F 18) dynamic frames (60 s each) using standard reconstruction (2D attenuation weighted ordered subsets expectation maximization). Patient motion correction was achieved by an image-based registration scheme optimizing a cost function using modified normalized cross-correlation that combined global and local features. For comparison, visual scoring of motion was performed on the scale of 0 to 2 (no motion, moderate motion, and large motion) by two experienced observers. RESULTS: The proposed registration technique had a 93% success rate in removing left ventricular motion, as visually assessed. The maximum detected motion extent for stress and rest were 5.2 mm and 4.9 mm for flurpiridaz F 18 perfusion and 3.0 mm and 4.3 mm for (82)Rb perfusion studies, respectively. Motion extent (maximum frame-to-frame displacement) obtained for stress and rest were (2.2 ± 1.1, 1.4 ± 0.7, 1.9 ± 1.3) mm and (2.0 ± 1.1, 1.2 ±0 .9, 1.9 ± 0.9) mm for flurpiridaz F 18 perfusion studies and (1.9 ± 0.7, 0.7 ± 0.6, 1.3 ± 0.6) mm and (2.0 ± 0.9, 0.6 ± 0.4, 1.2 ± 1.2) mm for (82)Rb perfusion studies, respectively. A visually detectable patient motion threshold was established to be ≥2.2 mm, corresponding to visual user scores of 1 and 2. After motion correction, the average increases in contrast-to-noise ratio (CNR) from all frames for larger than the motion threshold were 16.2% in stress flurpiridaz F 18 and 12.2% in rest flurpiridaz F 18 studies. The average increases in CNR were 4.6% in stress (82)Rb studies and 4.3% in rest (82)Rb studies. CONCLUSIONS: Fully automatic motion correction of dynamic PET frames can be performed accurately, potentially allowing improved image quantification of cardiac PET data.

Motion frozen (18)F-FDG cardiac PET.

BACKGROUND: PET reconstruction incorporating spatially variant 3D Point Spread Function (PSF) improves contrast and image resolution. "Cardiac Motion Frozen" (CMF) processing eliminates the influence of cardiac motion in static summed images. We have evaluated the combined use of CMF- and PSF-based reconstruction for high-resolution cardiac PET. METHODS: Static and 16-bin ECG-gated images of 20 patients referred for (18)F-FDG myocardial viability scans were obtained on a Siemens Biograph-64. CMF was applied to the gated images reconstructed with PSF. Myocardium to blood contrast, maximum left ventricle (LV) counts to defect contrast, contrast-to-noise (CNR) and wall thickness with standard reconstruction (2D-AWOSEM), PSF, ED-gated PSF, and CMF-PSF were compared. RESULTS: The measured wall thickness was 18.9 ± 5.2 mm for 2D-AWOSEM, 16.6 ± 4.5 mm for PSF, and 13.8 ± 3.9 mm for CMF-PSF reconstructed images (all P < .05). The CMF-PSF myocardium to blood and maximum LV counts to defect contrasts (5.7 ± 2.7, 10.0 ± 5.7) were higher than for 2D-AWOSEM (3.5 ± 1.4, 6.5 ± 3.1) and for PSF (3.9 ± 1.7, 7.7 ± 3.7) (CMF vs all other, P < .05). The CNR for CMF-PSF (26.3 ± 17.5) was comparable to PSF (29.1 ± 18.3), but higher than for ED-gated dataset (13.7 ± 8.8, P < .05). CONCLUSION: Combined CMF-PSF reconstruction increased myocardium to blood contrast, maximum LV counts to defect contrast and maintained equivalent noise when compared to static summed 2D-AWOSEM and PSF reconstruction.

Enhanced definition PET for cardiac imaging.

BACKGROUND: We aimed to determine in phantom and cardiac clinical studies the impact of a new high-resolution PET image reconstruction. METHODS: A phantom with cardiac insert filled with (18)F, 14 (18)F-FDG viability studies and 15 (82)Rb perfusion studies were acquired on a Siemens Biograph-64 (4-ring). The data were reconstructed with 2D- and 3D-attenuation weighted ordered subsets expectation maximization (AWOSEM), and high-definition reconstruction (HD.PET). We calculated wall/cavity contrast, contrast-to-noise ratio (CNR), wall thickness, motion/thickening and ejection fraction. RESULTS: In the phantom study, we found an increase in defect size (up to 26%), contrast (up to 48%) and CNR (1.9) with HD.PET as compared to standard techniques. The contrast increased on HD.PET images compared to 2D- and 3D-AWOSEM for viability (14.0% +/- 4.8%) and perfusion studies (7.3% +/- 4.3%) (P < .05). Average CNR increased with HD.PET by 79.4% +/- 17.1% and 68.8% +/- 3.0% in viability and perfusion studies respectively (all P < .05). Average wall thickness with HD.PET decreased in the phantom study by 1.3 +/- 0.3 mm and the viability studies by 1.9 +/- 0.7 mm but not in the perfusion studies. The functional measurements were not significantly different for any techniques. CONCLUSIONS: We demonstrated both in phantom and patient cardiac studies that HD.PET improves image contrast, defect definition, and CNR.

Coronary artery calcium scoring using a reduced tube voltage and radiation dose protocol with dual-source computed tomography.

BACKGROUND: Technical advances to minimize radiation exposure because of imaging are in accord with the "as low as reasonably achievable" principle. OBJECTIVE: We aimed to determine whether coronary calcium scoring (CCS) by multidetector CT at a tube voltage of 100 kVp yields comparable results to the standard 120-kVp protocol while reducing radiation dose. METHODS: Sixty consecutive outpatients were scanned with a dual-source CT scanner with both the120- and 100-kVp protocols. The calcium threshold was 130 Hounsfield units (HUs) for 120 kVp and 147 HU for 100 kVp, as determined from phantom data. All 100-kVp scans were scored by an experienced reader blinded to 120-kVp data. RESULTS: Image quality was comparable for 100- and 120- kVp scans. Mean Agatston scores for 100 and 120 kVp were 189 +/- 484 and 189 +/- 498 (P = 0.92), with perfect correlation (r = 1.0; P < 0.0001; 95% limits of agreement, -36 to 37; bias, 0.6). Mean coronary calcium volume scores for 100 and 120 kVp were 143 +/- 370 mm(3) and 149 +/- 392 mm(3) (P = 0.26), with perfect correlation (r = 1.0; P < 0.0001; 95% limits of agreement, -35 to 32 mm(3); bias, -1.4 mm(3)). The mean absolute difference for Agatston scores between the protocols was 16.9, with excellent agreement (kappa = 0.95; P < 0.0001). Mean effective radiation dose for the 100-kVp protocol was significantly lower (1.17 mSv versus 1.70 mSv; P < 0.0001). CONCLUSION: A reduced tube current protocol using 100 kVp gives equivalent CCS results at reduced radiation exposure compared with a standard protocol at 120 kVp.

Image quality and artifacts in coronary CT angiography with dual-source CT: initial clinical experience.

INTRODUCTION: We aimed to characterize artifacts observed in a routine clinical coronary CT angiography (CCTA) performed by a dual-source CT (DSCT) scanner (Definition; Siemens Medical Solutions). METHODS: Studies of 167 consecutive patients referred for CCTA, performed after beta-blockade (if not contraindicated), were prospectively analyzed for artifacts with a predefined visual approach. American Heart Association coronary segments (n = 2589) were assessed in 40%-80% R-R interval phases by 2 experts for stenosis, plaque presence or composition, and presence or type of artifacts. Each segment was considered evaluable when image quality was diagnostic in at least one cardiac phase. Artifacts included motion (cardiac, respiratory, patient), phase misregistration because of varying heart beats, calcified plaque blooming or beam hardening, metal beam hardening, large patient size, and contrast timing error. RESULTS: Maximum HR (HR) during CCTA ranged from 45 to 120 beats/min (66.4 +/- 14.8 beats/min). Artifacts of some type were observed in 69 (41.3%) of 167 studies. Calcified plaque was the most common source of artifacts (14.4%), followed by misregistration (13.8%). Only 25 (1%) of 2589 coronary segments, in 6 (4%) of 167 patients were unevaluable, primarily because of calcified plaque blooming (coronary calcium score [CCS], 1112 +/- 1255]. Artifacts were associated with CCS (P = 0.002), change in HR (P = 0.01), age (P = 0.03), and body mass index (P = 0.048). The optimal phase for evaluation of all coronary arteries was 70% (mid-diastole), with a shift toward the systolic phases for HR > 70 beats/min. CONCLUSION: CCTA artifacts with DSCT were related primarily to calcified plaque and cardiac phase misregistration. When correctly recognized, the artifacts did not have a serious effect on the final interpretation.

Algorithm for radiation dose reduction with helical dual source coronary computed tomography angiography in clinical practice.

BACKGROUND: Strategies to reduce the radiation dose of coronary computed tomography angiography (CCTA), while maintaining diagnostic image quality, are imperative for cardiac CT. OBJECTIVE: We aimed to reduce radiation dose during helical dual-source CCTA by combining lower tube voltage, shortest possible full tube current (FTC) window, and minimal tube current outside the FTC window, and to develop a patient-based algorithm for applying these dose-reduction components. METHODS: We compared FTC at 70% of the cardiac cycle (FTC70) to a 45% to 75% window (FTC45-75) using both 100 and 120 kVp (N=118). FTC70 was used in patients with heart rates <70 beats/min, no arrhythmia, age <65 years; 100 kVp was used in patients with body mass index (BMI) <30, a low coronary calcium score (CCS), and no stents. Objective and subjective image quality were assessed. RESULTS: Compared with FTC45-75 at 120 kVp, radiation dose was reduced by 66% for FTC70 at 100 kVp (mean radiation dose: 4.4 +/- 0.9 mSv) and by 43% for FTC70 at 120 kVp. 99% of 780 segments in the FTC70 group were of diagnostic quality. Noise, signal-to-noise ratio, and contrast-to-noise ratio were comparable between FTC70 and FTC45-75 for both 100 and 120 kVp. BMI, CCS and maximal heart rate variation were predictors of image quality. Tube voltage, FTC window width, scan length, and average heart rate were predictors of radiation dose. CONCLUSIONS: A successful patient-based algorithm for radiation dose reduction during helical CCTA using DSCT has been developed and validated in clinical practice.

Comparison of myocardial perfusion 82Rb PET performed with CT- and transmission CT-based attenuation correction.

UNLABELLED: CT-based attenuation correction (AC) for myocardial perfusion PET studies is challenging because of respiratory motion. Our study aimed to compare the transmission CT (TCT)-based and CT-based AC for myocardial perfusion PET/CT images with a direct semiquantitative approach comparing differences in segmental count distribution. METHODS: Stress and rest (82)Rb PET scans from 54 consecutive patients acquired on a PET/CT scanner with dual CT-based and TCT-based AC were considered. TCT- and CT-based AC images were automatically registered to each other, and direct voxel-based and American Heart Association segment-based estimation of positive and negative changes between these scans was performed. Additionally, visual quality control (QC) of CT map alignment with PET emission data was performed by 2 expert observers, and studies with significant (>/=5 mm) misalignment were reprocessed with corrected CT alignment. RESULTS: We used the 17-segment American Heart Association model for TCT-to-CT regional change analysis in all patients and found that 4 segments on rest and 4 segments on stress scans differed more than 3% between CT- and TCT-corrected images for studies without significant misalignments (<5 mm); only 1 differed by more than 5%. In cases with significant misalignment of greater than or equal to 3% TCT-CT AC, changes were observed on 14 rest and 10 stress segments; after alignment, these differences were still seen in 13 rest segments and 11 stress segments. Visual QC revealed that 46% of rest and 54% of stress PET scans were misaligned by greater than or equal to 5 mm with the CT maps acquired during normal breathing. The range of the reported PET/CT misalignment was 0-15 mm in x, 0-16 mm in y, and 0-20 mm in z directions. The overall agreement in visual QC of PET/CT alignment between the observers was 72.2% CONCLUSION: There are significant differences between TCT and CT AC applied to cardiac PET/CT studies, which remain after alignment of CT maps to emission data.

PET/CT imaging: effect of respiratory motion on apparent myocardial uptake.

BACKGROUND: Positron emission tomography (PET) attenuation correction (AC) using computed tomography (CT) can be affected by respiratory motion: hi-speed CT captures 1 point of the respiratory cycle while PET emission data averages many cycles. We quantified the changes in apparent myocardial uptake due to this respiratory-induced CT attenuation mismatch. METHODS: Twenty-two patients undergoing fluorine-18 fluorodeoxyglucose (FDG) PET/CT received 3 sequential CT scans at normal resting end-inspiration (CT(INSPIR)), ending expiration (CT(EXPIR)), and at midvolume between end-expiration and end-inspiration (CT(MIDVOL)). A pneumotachometer measured absolute changes in lung volume. Seven subjects also underwent a 3-minute transmission scan with a 68Ge rotating rod source (RRS). The PET emission data set was reconstructed up to 4 times using CT(EXPIR), CT(INSPIR), CT(MIDVOL), and RRS AC maps. Relative heart position and cardiac uptake was measured for each CT attenuation correction. RESULTS: Respiratory motion produced marked changes in global and regional myocardial uptake. Changes were large in the lateral and anterior regions at the lung-soft tissue interface (up to 30% using CT(INSPIR) compared to CT(EXPIR) for AC) and smaller in the septal region (10% or less). Data corrected with CT(EXPIR) agreed best with the RRS. CONCLUSION: Respiratory effects can introduce large inhomogeneities in apparent myocardial uptake when CT is used for attenuation correction.