Comparison of 2-dimensional and 3-dimensional cardiac 82Rb PET studies.

Most new PET scanners have the capability to collect data in 3-dimensional (3D) (septa removed) mode. This allows many more detected events at the cost of increased random events and scatter. In the case of 82Rb imaging, the injected dose might have to be limited to avoid saturating the scanner. We present a comparison of 2-dimensional (2D) and 3D data collection for 82Rb cardiac studies using the ECAT EXACT scanner. METHODS: Resting 82Rb cardiac studies were collected in 2D and 3D modes for 33 consecutive patients. Four experienced physicians rated the images to determine if the different acquisition methods would lead to different patient care. A separate quantitative analysis was performed on data from multiple scans of a thoracic phantom filled to simulate cardiac and background radioactivity corresponding to 82Rb injections between 37 and 1740 MBQ: RESULTS: The 2D and 3D studies were significantly different, with the image quality being poorer in the 3D studies. The scanner collected data at near its maximal counting rate for either 1480-MBq 2D or 37-MBq 3D acquisitions. Because the data collection was counting rate limited in either mode, and there are more random and scatter events in 3D mode, the 2D acquisitions resulted in more detected true events and a better signal-to-noise ratio. CONCLUSION: Cardiac 82Rb studies should be performed in 2D mode when using the ECAT EXACT scanner.     

Quantitative dynamic cardiac 82Rb PET using generalized factor and compartment analyses.

We have addressed 2 major challenges of (82)Rb cardiac PET, noninvasive estimation of an accurate input function and absolute quantitation of myocardial perfusion, using a generalized form of least-squares factor analysis of dynamic sequences (GFADS) and a novel compartment analysis approach. METHODS: Left and right ventricular (LV + RV) time-activity curves (TACs) were generated from 10 rest/stress studies, and 30 myocardial TACs were modeled to cover a range of clinical values. Two-dimensional PET Monte Carlo simulations of the LV, RV, myocardium, and other organs were generated separately and combined using the above TACs to form 30 realistic dynamic (82)Rb studies. LV and RV TACs were estimated by GFADS and used as input to a 2-compartment kinetic analysis that estimates parametric maps of myocardial tissue extraction (k(1)) and egress (k(2)), as well as LV + RV contributions (f(v), r(v)), by orthogonal voxel grouping. In addition, 13 patients were injected with 2.22 +/- 0.19 GBq (60 +/- 5 mCi) of (82)Rb and imaged dynamically for 6 min at rest and during dipyridamole stress. RESULTS: In Monte Carlo simulations, GFADS yielded estimates of the 3 factors and corresponding factor images, with average errors of -4.2% +/- 6.3%, 3.5% +/- 4.3%, and 2.0% +/- 5.5% in the LV, RV, and myocardial factor estimates, respectively. The estimates were significantly more accurate and robust to noise than those obtained using TACs based on manually drawn volumes of interest (P < 0.01). The 2-compartment approach yielded accurate k(1), k(2), f(v), and r(v) parametric maps; the average error of estimates of k(1) was 6.8% +/- 3.6%. In all patient studies, our approach yielded robust estimates of k(1), k(2), f(v), and r(v), which correlated very well with the status of the subject and the catheterization results. CONCLUSION: Quantitative dynamic (82)Rb PET using generalized factor analysis of dynamic sequences and compartmental modeling yields estimates of parameters of absolute myocardial perfusion and kinetics with errors of <9%.     

Absolute quantification of myocardial blood flow with 13N-ammonia and 3-dimensional PET.

The aim of this study was to compare 2-dimensional (2D) and 3-dimensional (3D) dynamic PET for the absolute quantification of myocardial blood flow (MBF) with (13)N-ammonia ((13)N-NH(3)). METHODS: 2D and 3D MBF measurements were collected from 21 patients undergoing cardiac evaluation at rest (n = 14) and during standard adenosine stress (n = 7). A lutetium yttrium oxyorthosilicate-based PET/CT system with retractable septa, enabling the sequential acquisition of 2D and 3D images within the same patient and study, was used. All 2D studies were performed by injecting 700-900 MBq of (13)N-NH(3). For 14 patients, 3D studies were performed with the same injected (13)N-NH(3) dose as that used in 2D studies. For the remaining 7 patients, 3D images were acquired with a lower dose of (13)N-NH(3), that is, 500 MBq. 2D images reconstructed by use of filtered backprojection (FBP) provided the reference standard for MBF measurements. 3D images were reconstructed by use of Fourier rebinning (FORE) with FBP (FORE-FBP), FORE with ordered-subsets expectation maximization (FORE-OSEM), and a reprojection algorithm (RP). RESULTS: Global MBF measurements derived from 3D PET with FORE-FBP (r = 0.97), FORE-OSEM (r = 0.97), and RP (r = 0.97) were well correlated with those derived from 2D FBP (all Ps < 0.0001). The mean +/- SD differences in global MBF measurements between 3D FORE-FBP and 2D FBP and between 3D FORE-OSEM and 2D FBP were 0.01 +/- 0.14 and 0.01 +/- 0.15 mL/min/g, respectively. The mean +/- SD difference in global MBF measurements between 3D RP and 2D FBP was 0.00 +/- 0.16 mL/min/g. The best correlation between 2D PET and 3D PET performed with the lower injected activity was found for the 3D FORE-FBP reconstruction algorithm (r = 0.95, P < 0.001). CONCLUSION: For this scanner type, quantitative measurements of MBF with 3D PET and (13)N-NH(3) were in excellent agreement with those obtained with the 2D technique, even when a lower activity was injected.     

Improving 3D PET imaging by restoration: a phantom study.

The main objective of our work is to improve 3D PET imaging. Compared with 2D PET, 3D PET imaging has slightly worse axial resolution and a significantly higher contribution of scatter and randoms, but 3D PET has much better sensitivity than 2D PET imaging. A Jaszczak deluxe phantom was acquired in 3D mode on our GE Advance PET system. Activity of 333 MBq of 18F was uniformly distributed. Prior to the emission scan, blank and transmission scans had been acquired. They were used for attenuation correction. The duration of the emission scan was 20 min, transmission 10 min, and blank 20 min. Standard FBP reconstruction software provided by the vendor was used to obtain slice images. Point spread function was also acquired in a 21 cm diameter cylinder phantom filled with water 6.0 cm from the center and used to create restoration filters. Two restoration filters were applied, medium and sharp. Results showed significant improvement in resolution, contrast and detectability of the cold rods. The artifacts outside the phantom were also significantly reduced. For 11.1 mm rods, average contrast was 0.49+/-0.02 in the original image, 0.52+/-0.04 in the medium restored image, and in the sharply restored image 0.75+/-0.05. For 7.9 mm rods, average contrast was 0.07+/-0.01 in the original image, 0.21+/-0.03 in the medium restored image, and 0.50+/-0.04 in the sharply restored image. The amount of noise in the uniform slices, measured as the coefficient of variation (COV), was 5.5, 7.1 and 10.8% in the original image and in the images restored with medium and sharp filters, respectively. In conclusion, restoration can significantly improve the resolution and contrast of 3D PET imaging.     

Comparison of 2-dimensional and 3-dimensional acquisition for 18F-FDG PET oncology studies performed on an LSO-based scanner.

Three-dimensional (3D) PET acquisition has the potential to reduce image noise but the advantage of 3D PET for studies outside the brain has not been well established. To compare the performance of 2-dimensional (2D) and 3D acquisition for whole-body (18)F-FDG applications, a series of patient studies were performed using a lutetium oxyorthosilicate (LSO)-based tomograph. METHODS: Comparative 2D and 3D images were acquired for 27 oncology patients using an LSO-based tomograph. Data acquisition (350-650 keV, 6 ns) started 99 +/- 12 min (mean +/- SD) after injection of 624 +/- 76 MBq (18)F-FDG. Bias caused by tracer redistribution and decay was eliminated by acquiring dynamic data over a single-bed position using a protocol that alternated between septa-in and septa-out modes (2D, 3D, 2D, 3D, 2D, 3D). Frames were combined to form 8 statistically independent sinograms: four 2D replicates (105 s) and four 3D replicates (90 s). The different frame durations in 2D and 3D compensated for the different number of overlapping bed positions required for an 85-cm whole-body study. Images were reconstructed with either 2D or fully 3D ordered-subsets expectation maximization (2 iterations and 8 subsets; 2D 6-mm gaussian, 3D 5- and 6-mm gaussian). Image target-to-background ratio was assessed by dividing the lesion maximum by the mean within a neighboring background region. Image noise was assessed by applying background regions of interest to the replicate images and calculating the within-patient coefficient of variation. RESULTS: The difference in target-to-background ratio between the 2D and 3D images, when they were filtered with 6-mm and 5-mm gaussian filters, respectively, was not highly statistically significant (P = 0.16). The mean ratio of 3D to 2D image values was 0.94 with 95% limits of agreement of 0.63-1.41. The within-patient coefficients of variation for the 2D and 3D images were 13% +/- 15% and 9% +/- 10%, respectively (P = 0.0005). CONCLUSION: Under conditions of matched target to-to-background ratios, the 3D mode was found to produce images with significantly less variability than the 2D mode. These data provide support for the use of 3D acquisition with LSO detectors to reduce scan times in whole-body (18)F-FDG applications.     

Feedback-assisted three-dimensional reconstruction of the left ventricle with MRI

PURPOSE: To develop and test a new technique for rapid, accurate three-dimensional (3D) reconstruction of the left ventricle (LV) and calculation of its volume parameters, with images from multiple orientations and interactive feedback. MATERIALS AND METHODS: The ventricular surface was fit to a number of user-placed guide points in magnetic resonance (MR) images using bivariate smoothing splines. A 3D model was reconstructed and the LV volumes were calculated at both end diastole (ED) and end systole (ES). This technique was validated using a phantom, and applied to studies of 18 patients and four volunteers (N = 22) imaged on a 1.5-T clinical scanner. The results of the 3D method were compared to the standard 2D short-axis slice summation technique, which is widely used for the analysis of cardiac function. RESULTS: There was excellent agreement between the computed volume of the phantom using the 3D modeling method and the actual volume (190.50 mL +/- 3.06 mL, and 191.0 mL +/- 2.5 mL, respectively). There was good correlation between the volumes calculated with our 3D model and the slice summation technique (ED volume (EDV) difference, 6.36% +/- 8.99% [mean +/- SD]; ES volume (ESV), 0.92% +/- 14.75%; stroke volume (SV), 10.54% +/- 13.95%; ejection fraction (EF), 4.22% +/- 9.16%). The 3D method was found to be more accurate than the slice summation technique for calculating LV volumes and mass from images of different slice orientations. Variations in the parameters between the two separate orientations using the 3D model vs. the slice summation method were as follows: EDV: 2.11% +/- 1.52% vs. 10.36% +/- 9.33%; ES volume: 2.76% +/- 1.64% vs. 6.39% +/- 3.62%; SV, 3.02% +/- 4.38% vs. 18.84% +/- 15.30%; EF, 2.03% +/- 2.16% vs. 8.58% +/- 6.73%; and LV mass: 4.77% +/- 2.41% vs. 24.59% +/- 6.41%. Differences in the ES volume due to the inclusion or exclusion of the most basal slice were found to be lower with the 3D model (6.90% +/- 3.83%) compared to the slice summation method (25.04% +/- 6.15%). CONCLUSION: 3D models can be used to accurately determine ventricular volume parameters. Results can be obtained using images from a variety of orientations, providing greater flexibility during image acquisition and possibly reducing the number of images needed for analysis. Feedback is provided to assist the analysis by providing a continuous update of the LV shape and volume. This feature allows the user to determine LV parameters to a predefined accuracy or to terminate the analysis when the parameters are not changing. This method is not restricted to multislice cine imaging in a single or prescribed slice orientation, and can be used for quick, accurate, and interactive analysis of cardiac function.     

A lesion detection observer study comparing 2-dimensional versus fully 3-dimensional whole-body PET imaging protocols.

We compared the impact of 2-dimensional (2D) and fully 3-dimensional (3D) acquisition modes on the performance of human observers in detecting and localizing tumors in whole-body (18)F-FDG images. METHODS: We selected protocols based on noise equivalent count (NEC) rates derived from a series of 2D and fully 3D whole-body patient and phantom acquisitions on a dual-mode PET scanner. The fully 3D peak NEC value for a standard 70-kg patient was achieved for an injected dose of approximately 444 MBq (12 mCi) assuming a 90-min delay before acquisition, whereas the 2D peak value was never reached. The protocols were therefore set to those corresponding to a 444-MBq injected dose in fully 3D and 2D and a 740-MBq (20 mCi) injected dose in 2D that was considered as the maximum allowable dose. We used a non-Monte Carlo simulator to generate multiple realizations of whole-body PET data based on the geometry of the mathematic cardiac torso phantom (MCAT) with accurate noise properties. Two-dimensional and fully 3D acquisition times were set to 5 min per bed position. Spherical 1-cm-diameter lesions (targets) with random locations and contrasts were distributed in different organs. The simulated 2D datasets were reconstructed using attenuation-weighted ordered-subsets expectation maximization ((AW)OSEM) and the fully 3D datasets were reconstructed with FORE+(AW)OSEM (FORE = Fourier rebinning). Five human observers located and ranked the targets using a volumetric display of the whole-body PET data to replicate the clinical practice. An alternate free-response operating characteristic (AFROC) analysis of the human observer reports was performed for each protocol and each organ separately. RESULTS: The 2D protocol corresponding to 740-MBq injected dose allowed the overall best detection performance. It was followed by the fully 3D acquisition at the peak fully 3D NEC rate from a 444-MBq injected dose. A 2D acquisition corresponding to a 444-MBq injected dose was ranked last. Differences in detection performance were organ specific. CONCLUSION: This study showed that, for this patient size and scanner type, the fully 3D acquisition mode allowed better or equivalent detection performance than the 2D mode for an injected dose corresponding to the peak fully 3D NEC rate. The 2D acquisition protocol combined with a higher injected dose resulted in the highest detectabilities.     

Respiratory gating for 3-dimensional PET of the thorax: feasibility and initial results.

Respiratory motion may reduce the sensitivity of (18)F-FDG PET for the detection of small pulmonary nodules close to the base of the lungs. This motion also interferes with attempts to use fused PET/CT images through software or combined PET/CT devices. This study was undertaken to assess the feasibility of respiratory gating for PET of the chest and the impact of respiratory motion on quantitative analysis. METHODS: Ten healthy subjects were enrolled in this study. Three-dimensional studies were acquired with 8 gates per respiratory cycle on a commercial PET scanner with a temperature-sensitive respiratory gating device built in-house. All scans were obtained over 42 cm of body length with 3 bed positions of 10 min each after injection of (18)F-FDG at 4.5 MBq/kg. The reconstructed images were assembled to produce gated whole-body volumes and maximum-intensity projections. The amplitude of respiratory motion of the kidneys (as a surrogate for diaphragmatic incursion) as well as the apex of the heart was measured in the coronal plane. Phantom studies were acquired to simulate the impact of respiratory motion on quantitative uptake measurements. RESULTS: The respiratory gating device produced a consistent, reliable trigger signal. All acquisitions were successful and produced reconstructed volumes with excellent image quality. Mean +/- SD motion amplitude and maximal motion amplitude values were 6.7 +/- 3.0 and 11.9 mm for the heart, 12.0 +/- 3.7 and 18.8 mm for the right kidney, and 11.1 +/- 4.8 and 17.1 mm for the left kidney, respectively. In phantom studies, the standardized uptake value for a 1-mL lesion was underestimated by 30% and 48% for the average and maximal respiratory motion values, respectively. CONCLUSION: Respiratory gating of PET of the thorax and upper abdomen is a practical and feasible approach that may improve the detection of small pulmonary nodules. Further work is planned to assess prospectively the diagnostic accuracy of this new method.     

Myocardial viability assessment by PET: (82)Rb defect washout does not predict the results of metabolic-perfusion mismatch.

PET is a sensitive technique for the identification of viable myocardial tissue in patients with coronary disease. Metabolic assessment with (18)F-FDG is considered the gold standard for assessment of viability before surgical revascularization. Prior research has suggested that viability may be assessed with washout of (82)Rb between early and late resting images. Our objective was to determine whether assessment of myocardial viability with (82)Rb washout is reliable when compared with PET using (18)F-FDG. METHODS: We performed PET for 194 patients referred for PET (18)F-FDG/(82)Rb to assess viability for clinical indications. We included 151 patients with resting defects >10% of the left ventricle (LV) (n = 159 defects). Patients with smaller resting (82)Rb defects (<10% LV) were excluded for the purpose of this study. PET images acquired with (82)Rb and (18)F-FDG defined viability by the mismatch between metabolism and perfusion ((18)F-FDG >125% of (82)Rb uptake in the (82)Rb defect). Evidence of viability with (82)Rb was assessed by the presence of (i) severity: (82)Rb counts in the defect >50% of (82)Rb in the normal zone of the resting PET images; (ii) washout: decrease of (82)Rb counts in the defect from early to late resting (82)Rb images <17% between the first 90-s image and the final 300-s image; or (iii) combined severity and washout criteria, which required positive criteria for (i) and (ii) to indicate viability. RESULTS: Prevalence of viability by (18)F-FDG/(82)Rb criteria was 50% (n = 79). Severity criteria yielded a sensitivity of 76% and a specificity of 17%, washout criteria yielded a sensitivity of 81% and a specificity of 23%, and both criteria had a sensitivity of 63% and a specificity of 32%. Positive and negative predictive values were poor for all criteria. No correlation existed between (82)Rb washout and (18)F-FDG-(82)Rb mismatch (r(2) = 0.00). Multiple receiver-operating-characteristic plots showed very poor discrimination despite varying criteria for viability by (82)Rb (severity from 50% to 60% of normal zone, washout from 12% to 17%). CONCLUSION: (82)Rb washout from early to late resting images, combined with quantitative severity of the resting (82)Rb defect, did not yield results equivalent to PET (18)F-FDG-(82)Rb mismatch and may not accurately assess myocardial viability.     

Cardiac pacemakers and central venous lines can induce focal artifacts on CT-corrected PET images.

PET/CT imaging can be associated with focal artifactual (18)F-FDG uptake introduced by metallic implants or contrast agents. It is unknown whether cardiac pacemakers or permanent central venous catheters can also result in such artifacts. METHODS: Twenty-seven patients with permanent central venous lines (13 men and 14 women; mean age +/- SD, 53.8 +/- 16.2 y) and 9 patients with pacemakers (7 men and 2 women; mean age +/- SD, 74.8 +/- 5.1 y) who were referred for a variety of oncologic indications were studied with lutetium-oxyorthosilicate-based dual-slice PET/CT after injection of 7.77 MBq/kg of (18)F-FDG. CT-corrected and -uncorrected PET images were reviewed, and (18)F-FDG uptake was graded as absent, mild, moderate, or intense. RESULTS: CT-corrected PET images revealed focally increased uptake of moderate intensity in all patients with cardiac pacemakers and focally increased uptake of mild intensity in 8 of 27 patients (29.6%) with central venous lines. CONCLUSION: Cardiac pacemakers and reservoirs of central venous lines can induce artifactual (18)F-FDG on CT-corrected PET images. Thus, in patients with permanent central lines or pacemakers, both corrected and uncorrected PET images need to be reviewed to avoid false-positive PET findings.     

Human biodistribution and radiation dosimetry of the tachykinin NK1 antagonist radioligand [18F]SPA-RQ: comparison of thin-slice, bisected, and 2-dimensional planar image analysis.

(18)F-Labeled substance P antagonist-receptor quantifier ([(18)F]SPA-RQ) [2-fluoromethoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-[(2S,3S)-2-phenyl-piperidin-3-yl)amine] is a selective radioligand for in vivo quantification of tachykinin NK(1) receptors with PET. The aims of this study were to estimate the radiation safety profile and relative risks of [(18)F]SPA-RQ with 3 different methods of image analysis. METHODS: Whole-body PET images were acquired in 7 healthy subjects after injection of 192 +/- 7 MBq (5.2 +/- 0.2 mCi) [(18)F]SPA-RQ. Emission images were serially acquired at multiple time-points from 0 to 120 min and approximately 180-240 min after injection. Urine samples were collected after each imaging session and for 24 h after the last scan to measure excreted radioactivity. Horizontal tomographic images were compressed to varying degrees in the anteroposterior direction to create 3 datasets: thin-slice, bisected, and 2-dimensional (2D) planar images. Regions of interest were drawn around visually identifiable source organs to generate time-activity curves for each dataset. Residence times were determined from these curves, and doses to individual organs and the body as a whole were calculated using OLINDA/EXM 1.0. RESULTS: The lungs, upper large intestine wall, small intestine, urinary bladder wall, kidneys, and thyroid had the highest radiation-absorbed doses. Biexponential fitting of mean bladder and urine activity showed that about 41% of injected activity was excreted via urine. Assuming a 2.4-h urine voiding interval, the calculated effective doses from thin-slice, bisected, and 2D planar images were 29.5, 29.3, and 32.3 microSv/MBq (109, 108, and 120 mrem/mCi), respectively. CONCLUSION: Insofar as effective dose is an accurate measure of radiation risk, all 3 methods of analysis provided quite similar estimates of risk to human subjects. The radiation dose was moderate and would potentially allow subjects to receive multiple PET scans in a single year. Individual organ exposures varied among the 3 methods, especially for structures asymmetrically located in an anterior or posterior position. Bisected and 2D planar images almost always provided higher organ dose estimates than thin-slice images. Thus, either the bisected or 2D planar method of analysis appears acceptable for quantifying human radiation burden, at least for radioligands with a relatively broad distribution in the body and not concentrated in a small number of radiation sensitive organs.     

Prognostic significance of dipyridamole-induced ST depression in patients with normal 82Rb PET myocardial perfusion imaging.

Recent studies have shown that vasodilator-induced ischemic electrocardiographic (ECG) changes have incremental prognostic value over normal SPECT myocardial perfusion imaging (MPI) and identify patients at higher risk for cardiac events. The prognostic value of vasodilator-induced ischemic ECG changes in the setting of normal PET MPI has yet to be determined. We sought to determine the prognostic importance of dipyridamole-induced ischemic ECG changes in patients with normal 82Rb PET myocardial perfusion images. METHODS: Between 2000 and 2003, 2,029 consecutive patients undergoing dipyridamole stress 82Rb PET at the University of Ottawa Heart Institute were evaluated. Patients with normal PET MPI and interpretable ECGs were enrolled. Electrocardiograms were assessed for ST depression or elevation and patients were categorized into those with and without dipyridamole-induced ischemic ECG changes. Images were graded using the 17-segment model. Follow-up information was obtained by telephone interview, from hospital records, or from treating physicians. All cardiac events (cardiac death, nonfatal myocardial infarction [MI], percutaneous coronary intervention, coronary artery bypass grafting, or angiography) were verified with hospital records. RESULTS: Of the 629 enrolled patients with normal PET MPI, 72 patients had dipyridamole-induced ischemic ECG changes. There was no significant difference between the 2 groups in the combined endpoint (cardiac death, nonfatal MI, and revascularization) at follow-up (mean +/- SD, 27.1 +/- 13 mo). There were no cardiac deaths in either group. One (1.4%) patient with ischemic ECG changes had a nonfatal MI (0.6% annual event rate). Two (2.8%) patients with ischemic ECG changes required revascularization compared with 11 (2.0%) in the nonischemic ECG group. CONCLUSION: Normal 82Rb PET confers an excellent prognosis regardless of dipyridamole-induced ST depression.     

Acquisition settings for PET of 124I administered simultaneously with therapeutic amounts of 131I.

Radiation dosimetry of thyroid cancer therapy with 131I can be performed by coadministration of 124I followed by longitudinal PET scans over several days. The photons emitted by 131I may affect PET image quality. The aim of this study was to assess the influence of large amounts of 131I on PET image quality and accuracy with various acquisition settings. METHODS: Noise equivalent count (NEC) rates of 124I only were measured with a standard clinical PET scanner. Apart from the standard 350- to 650-keV energy window, 425- to 650-keV and 460- to 562-keV windows were used and data were acquired both with (2-dimensional) and without (3-dimensional [3D]) septa. A phantom containing 6 hot spheres, filled with a combination of 131I and 124I and with a sphere-to-background ratio of 18:1, was scanned repeatedly with energy window settings as indicated and emission and transmission scan durations of 7 and 3 min, respectively. NEC rates were calculated and compared with those measured with the phantom filled with only 124I. Sphere-to-background ratios in the reconstructed images were determined. One patient with known metastatic thyroid cancer was scanned using energy window settings and scan times as indicated 3 and 6 d after administration of 5.5 GBq of 131I and 75 MBq of 124I. RESULTS: The highest 124I-only NEC rates were obtained using a 425- to 650-keV energy window in 3D mode. In the presence of (131)I, the settings giving the highest NEC rate and contrast were 425-650 keV and 460-562 keV in 3D mode, with the clinical scans giving the highest quality images with the same settings. CONCLUSION: Acquisition in 3D mode with a 425- to 650-keV or 460- to 562-keV window leads to the highest image quality and contrast when imaging 124I in the presence of large amounts of 131I using a standard clinical PET scanner.     

Quantification of cerebral blood flow and oxygen metabolism with 3-dimensional PET and 15O: validation by comparison with 2-dimensional PET.

Quantitative PET with (15)O provides absolute values for cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO(2)), and oxygen extraction fraction (OEF), which are used for assessment of brain pathophysiology. Absolute quantification relies on physically accurate measurement, which, thus far, has been achieved by 2-dimensional PET (2D PET), the current gold standard for measurement of CBF and oxygen metabolism. We investigated whether quantitative (15)O study with 3-dimensional PET (3D PET) shows the same degree of accuracy as 2D PET. METHODS: 2D PET and 3D PET measurements were obtained on the same day on 8 healthy men (age, 21-24 y). 2D PET was performed using a PET scanner with bismuth germanate (BGO) detectors and a 150-mm axial field of view (FOV). For 3D PET, a 3D-only tomograph with gadolinium oxyorthosilicate (GSO) detectors and a 156-mm axial FOV was used. A hybrid scatter-correction method based on acquisition in the dual-energy window (hybrid dual-energy window [HDE] method) was applied in the 3D PET study. Each PET study included 3 sequential PET scans for C(15)O, (15)O(2), and H(2)(15)O (3-step method). The inhaled (or injected) dose for 3D PET was approximately one fourth of that for 2D PET. RESULTS: In the 2D PET study, average gray matter values (mean +/- SD) of CBF, CBV, CMRO(2), and OEF were 53 +/- 12 (mL/100 mL/min), 3.6 +/- 0.3 (mL/100 mL), 3.5 +/- 0.5 (mL/100 mL/min), and 0.35 +/- 0.06, respectively. In the 3D PET study, scatter correction strongly affected the results. Without scatter correction, average values were 44 +/- 6 (mL/100 mL/min), 5.2 +/- 0.6 (mL/100 mL), 3.3 +/- 0.4 (mL/100 mL/min), and 0.39 +/- 0.05, respectively. With the exception of OEF, values differed between 2D PET and 3D PET. However, average gray matter values of scatter-corrected 3D PET were comparable to those of 2D PET: 55 +/- 11 (mL/100 mL/min), 3.7 +/- 0.5 (mL/100 mL), 3.8 +/- 0.7 (mL/100 mL/min), and 0.36 +/- 0.06, respectively. Even though the 2 PET scanners with different crystal materials, data acquisition systems, spatial resolution, and attenuation-correction methods were used, the agreement of the results between 2D PET and scatter-corrected 3D PET was excellent. CONCLUSION: Scatter coincidence is a problem in 3D PET for quantitative (15)O study. The combination of both the present PET/CT device and the HDE scatter correction permits quantitative 3D PET with the same degree of accuracy as 2D PET and with a lower radiation dose. The present scanner is also applicable to conventional steady-state (15)O gas inhalation if inhaled doses are adjusted appropriately.     

Myocardial FDG-PET examination during fasting and glucose loading states by means of a one-day protocol

We propose a new method to measure the myocardial FDG uptake during fasting and glucose loading in one day, a myocardial FDG-PET one-day protocol, with both 2- and 3-dimensional data acquisition (2D and 3D) without background activity subtraction. To confirm it, we evaluated the effect of scatter correction in the 2D and 3D modes of a PET scanner both in phantom and patient studies. In the phantom study, we used a cardiac phantom with six divided chambers and two cylindrical phantoms placed as the activity outside the field of view. Each chamber was filled with a different concentration of F- 18 solution. Regions of interest (ROI) were placed on a polar map generated from reconstructed images and were compared to the concentration of the solution in each chamber in both 2D and 3D. In the patient study, 10 non-diabetic patients with coronary artery disease were studied. Each patient received a myocardial FDG study during fasting (F) and glucose loading (L). L images with background subtraction (Lsub(+)) and without background subtraction (Lsub(-)) were compared by polar map analysis. The ROI counts for the true activity in 2D and 3D demonstrated a linear relationship, and quite similar slopes were observed (0.72 in 2D, 0.69 in 3D). The background fraction in Lsub(-) was 3.59+/-1.83%. There were significant differences between Lsub(-) or Lsub(+) and F in both normal and ischemic myocardium. Scatter correction was successfully performed in both 2D and 3D modes. Background activity is thought to be negligible and this proposed method is simple touse in measuring the myocardial FDG uptake in one day.     

Clinical usefulness of ultrashort-lived iridium-191m from a carbon-based generator system for the evaluation of the left ventricular function

Ultrashort-lived 191mIr (4.96 sec; 63-74 and 129 keV photons) is potentially advantageous for first-pass radionuclide angiocardiography, offering the opportunity to perform repeat studies with very low absorbed radiation dose to the patient. Left ventricular (LV) first-pass studies were performed in 72 patients with 191mIr from a new bedside 1.3 Ci (48.1 GBq) 191Os/191mIr generator system using an activated carbon support that offers high 191mIr yields (15-18%) and consistent low 191Os breakthrough (2-4 x 10(-4)%/bolus). Using a single crystal digital gamma camera, uncorrected end-diastolic counts in the left ventricular representative cycle ranged from 10 up to 30 k counts. The reproducibility of repeated LV ejection fraction (LVEF) determination at 2-min intervals in 50 patients was r = 0.97, mean diff. = 2.08 +/- 1.55 EF units. Comparison between 191mIr (80-120 mCi; 2,960-4,400 MBq) and 99mTc (20-25 mCi; 750-925 MBq) LV count rates indicates a 3 wk useful shelf life of this new generator system for cardiac studies. Iridium-191m determined LVEF correlated closely with 99mTc determined LVEF in 32 patients (r = 0.96, mean diff. = 1.87 +/- 1.23 EF units). Parametric images for LV wall motion analysis were comparable with both isotopes. We conclude that rapid, repeat, and reproducible high count rate first-pass left ventricular studies can be obtained with 191mIr from this new 191Os/191mIr generator system using a single crystal digital gamma camera.     

Quantification of regional myocardial blood flow estimation with three-dimensional dynamic rubidium-82 PET and modified spillover correction model

Purpose

Myocardial blood flow (MBF) estimation with ⁸²Rubidium (⁸²Rb) positron emission tomography (PET) is technically difficult because of the high spillover between regions of interest, especially due to the long positron range. We sought to develop a new algorithm to reduce the spillover in image-derived blood activity curves, using non-uniform weighted least-squares fitting.

Methods

Fourteen volunteers underwent imaging with both 3-dimensional (3D) ⁸²Rb and ¹⁵O-water PET at rest and during pharmacological stress. Whole left ventricular (LV) ⁸²Rb MBF was estimated using a one-compartment model, including a myocardium-to-blood spillover correction to estimate the corresponding blood input function Ca(t)^whole. Regional K1 values were calculated using this uniform global input function, which simplifies equations and enables robust estimation of MBF. To assess the robustness of the modified algorithm, inter-operator repeatability of 3D ⁸²Rb MBF was compared with a previously established method.

Results

Whole LV correlation of ⁸²Rb MBF with ¹⁵O-water MBF was better (P?<?.01) with the modified spillover correction method (r?=?0.92 vs r?=?0.60). The modified method also yielded significantly improved inter-operator repeatability of regional MBF quantification (r?=?0.89) versus the established method (r?=?0.82) (P?<?.01).

Conclusion

A uniform global input function can suppress LV spillover into the image-derived blood input function, resulting in improved precision for MBF quantification with 3D ⁸²Rb PET.     

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 comparison of analytic and iterative reconstruction methods in 2- and 3-dimensional dynamic cardiac 18F-FDG PET.

The aim of this work was to compare the quantitative accuracy of iteratively reconstructed cardiac (18)F-FDG PET with that of filtered backprojection for both 2-dimensional (2D) and 3-dimensional (3D) acquisitions and to establish an optimal procedure for imaging myocardial viability with (18)F-FDG PET. METHODS: Eight patients underwent dynamic cardiac (18)F-FDG PET using an interleaved 2D/3D scan protocol, enabling comparison of 2D and 3D acquisitions within the same patient and study. A 10-min transmission scan was followed by a 10-min, 25-frame dynamic 3D scan and then by a series of 10 alternating 5-min 3D and 2D scans. Images were reconstructed with filtered backprojection (FBP) or attenuation-weighted ordered-subsets expectation maximization (OSEM), combined with Fourier rebinning (FORE) for 3D acquisitions, applying all usual corrections. Regions of interest (ROIs) were drawn in the myocardium, left ventricle, and ascending aorta, with the last 2 being used to define image-derived input functions (IDIFs). Patlak graphical analysis was used to compare net (18)F-FDG uptake in the myocardium, calculated from either 2D or 3D data, after reconstruction with FBP or OSEM. Either IDIFs or arterial sampling was used as the input function. The same analysis was performed on parametric images. RESULTS: A good correlation (r(2) > 0.99) was found between net (18)F-FDG uptake values for a myocardium ROI determined using each acquisition and reconstruction method and blood-sampling input functions. A similar result was found for parametric images. The ascending aorta was the best choice for IDIF definition. CONCLUSION: Good correlation and no bias of net (18)F-FDG uptake in relation to that based on FBP images, combined with less image noise, make 3D acquisition with FORE plus attenuation-weighted OSEM reconstruction the preferred choice for cardiac (18)F-FDG PET studies.     

Gated cardiac 13N-NH3 PET for assessment of left ventricular volumes, mass, and ejection fraction: comparison with electrocardiography-gated 18F-FDG PET.

The purpose of this study was to evaluate myocardial electrocardiography (ECG)-gated 13N-ammonia (13N-NH3) PET for the assessment of cardiac end-diastolic volume (EDV), cardiac end-systolic volume (ESV), left ventricular (LV) myocardial mass (LVMM), and LV ejection fraction (LVEF) with gated 18F-FDG PET as a reference method. METHODS: ECG-gated 13N-NH3 and 18F-FDG scans were performed for 27 patients (23 men and 4 women; mean+/-SD age, 55+/-15 y) for the evaluation of myocardial perfusion and viability. For both 13N-NH3 and 18F-FDG studies, a model-based image analysis tool was used to estimate endocardial and epicardial borders of the left ventricle on a set of short-axis images and to calculate values for EDV, ESV, LVEF, and LVMM. RESULTS: The LV volumes determined by 13N-NH3 and 18F-FDG were 108+/-60 mL and 106+/-63 mL for ESV and 175+/-71 mL and 169+/-73 mL for EDV, respectively. The LVEFs determined by 13N-NH3 and 18F-FDG were 42%+/-13% and 41%+/-13%, respectively. The LVMMs determined by 13N-NH3 and 18F-FDG were 179+/-40 g and 183+/-43 g, respectively. All P values were not significant, as determined by paired t tests. A significant correlation was observed between 13N-NH3 imaging and 18F-FDG imaging for the calculation of ESV (r=0.97, SEE=14.1, P<0.0001), EDV (r=0.98, SEE=15.4, P<0.0001), LVEF (r=0.9, SEE=5.6, P<0.0001), and LVMM (r=0.93, SEE=15.5, P<0.0001). CONCLUSION: Model-based analysis of ECG-gated 13N-NH3 PET images is accurate in determining LV volumes, LVMM, and LVEF. Therefore, ECG-gated 13N-NH3 can be used for the simultaneous assessment of myocardial perfusion, LV geometry, and contractile function.