Use of [11C]acetate and [15O]O2 PET for the assessment of myocardial oxygen utilization in patients with chronic myocardial infarction

Carbon-11 acetate positron emission tomography (PET) has been widely used to assess regional oxidative metabolism of the heart. However, the accuracy of [11C]acetate PET in assessing oxidative metabolism in infarcted myocardium remains controversial. Thirteen patients with stable coronary artery disease and old myocardial infarction were studied. The 15O-based PET studies yielded regional blood flow (rMBF, ml/min/g) and oxygen consumption (rMMRO2, ml/min/g), which was compared with the myocardial clearance rate constant (kmono) of [11C]acetate in segments with rMBF > or = 75% (group A), 50%-74% (group B) or < 50% (group C) of the normal reference segment. Mean MBF was 0.96 +/- 0.08 ml/g/min in group A, 0.67 +/- 0.06 ml/g/min in group B and 0.42 +/- 0.07 ml/g/min in group C segments. The segmental rMMRO2 correlated linearly with kmono (r = 0.89, P < 0.001, y = 0.61x + 0.026). The kmono/rMMRO2 ratio was comparable in the group A and B segments (0.99 +/- 0.19 vs 1.07 +/- 0.21, P = NS). However, the ratio was significantly higher in the group C segments (1.28 +/- 0.35, P = 0.037). It is concluded that kmono of [11C]acetate correlates linearly with rMMRO2 determined by [15O]O2 inhalation. However, kmono appears to yield higher rMMRO2 estimates than the [15O]O2 method in low-flow areas.     

Improvement of algorithm for quantification of regional myocardial blood flow using 15O-water with PET.

(15)O-Water and dynamic PET allow noninvasive quantification of myocardial blood flow (MBF). However, complicated image analyzing procedures are required, which may limit the practicality of this approach. We have designed a new practical algorithm, which allows stable, rapid, and automated quantification of regional MBF (rMBF) using (15)O-water PET. We designed an algorithm for setting the 3-dimensional (3D) region of interest (ROI) of the whole myocardium semiautomatically. Subsequently, a uniform input function was calculated for each subject using a time-activity curve in the 3D whole myocardial ROI. The uniform input function allows the mathematically simple and robust algorithm to estimate rMBF. METHODS: Thirty-six volunteers were used in the static (15)O-CO and dynamic (15)O-water PET studies. To evaluate the reproducibility of the estimates, a repeated (15)O-water scan was obtained under resting condition. In addition, to evaluate the stability of the new algorithm in the hyperemic state, a (15)O-water scan was obtained with adenosine triphosphate. This algorithm includes a procedure for positioning a 3D ROI of the whole myocardium from 3D images and dividing it into 16 segments. Subsequently, the uniform input function was calculated using time-activity curves in the whole myocardial ROI and in the LV ROI. The uniform input function allowed this simple and robust algorithm to estimate the rMBF, perfusable tissue fraction (PTF), and spillover fraction (Va) according to a single tissue compartment model. These estimates were compared with those calculated using the original method. A simulation study was performed to compare the effects of errors in PTF or Va on the MBF using the 2 methods. RESULTS: The average operating time for positioning a whole myocardial ROI and 16 regional myocardial ROIs was <5 min. The new method yielded less deviation in rMBF (0.876 +/- 0.177 mL/min/g, coefficient of variation [CV] = 20.2%, n = 576) than those with the traditional method (0.898 +/- 0.271 mL/min/g, CV = 30.1%, n = 576) (P < 0.01). In the hyperemic state, the new method yielded less deviation in rMBF (3.890 +/- 1.250 mL/min/g, CV = 32.1%) than those with the traditional method (3.962 +/- 1.762 mL/min/g, CV = 44.4%) (P < 0.05). This method yielded significantly higher reproducibility of rMBF (r = 0.806, n = 576) than the original method (r = 0.756, n = 576) (P < 0.05). Our new method yielded a better correlation in the repeated measurement values of rMBF and less variability among the regions in the myocardium than with the original theory of the (15)O-water technique. The simulation study demonstrated fewer effects of error in the PTF or Va on the MBF value with the new method. CONCLUSION: We have developed a technique for an automated, simplified, and stable algorithm to quantify rMBF. This software is considered to be practical for clinical use in myocardial PET studies using (15)O-water with a high reproducibility and a short processing time.     

Clinical implications of different image reconstruction parameters for interpretation of whole-body PET studies in cancer patients.

The standardized uptake value (SUV) is the most commonly used parameter to quantify the intensity of radiotracer uptake in tumors. Previous studies suggested that measurements of (18)F-FDG accumulation in tissue might be affected by the image reconstruction method, but the clinical relevance of these findings has not been assessed. METHODS: Phantom studies were performed and clinical whole-body (18)F-FDG PET images of 85 cancer patients were analyzed. All images were reconstructed using either filtered backprojection (FBP) with measured attenuation correction (MAC) or iterative reconstruction (IR) with segmented attenuation correction (SAC). In a subset of 15 patients, images were reconstructed using all 4 combinations of IR+SAC, IR+MAC, FBP+SAC, and FBP+MAC. For phantom studies, a sphere containing (18)F-FDG was placed in a water-filled cylinder and the activity concentration of that sphere was measured in FBP and IR reconstructed images using all 4 combinations. Clinical studies were displayed simultaneously and identical regions of interest (ROIs, 50 pixels) were placed in liver, urinary bladder, and tumor tissue in both image sets. SUV max (maximal counts per pixel in ROI) and SUV avg (average counts per pixel) were measured. RESULTS: In phantom studies, measurements from FBP images underestimated the true activity concentration to a greater degree than those from IR images (20% vs. 5% underestimation). In patient studies, SUV derived from FBP images were consistently lower than those from IR images in both normal and tumor tissue: Tumor SUV max with IR+SAC was 9.6 +/- 4.5, with IR+MAC it was 7.7 +/- 3.5, with FBP+MAC it was 6.9 +/- 3.0, and with FBP+SAC it was 8.6 +/- 4.1 (all P < 0.01 vs. IR+SAC). Compared with IR+SAC, SUV from FBP+MAC images were 25%-30% lower. Similar discrepancies were noted for liver and bladder. Discrepancies between measurements became more apparent with increasing (18)F-FDG concentration in tissue. CONCLUSION: SUV measurements in whole-body PET studies are affected by the applied methods for both image reconstruction and attenuation correction. This should be considered when serial PET studies are done in cancer patients. Moreover, if SUV is used for tissue characterization, different cutoff values should be applied, depending on the chosen method for image reconstruction and attenuation correction.     

Bayesian image reconstruction for emission tomography based on median root prior

The aim of the present study was to investigate a new type of Bayesian one-step late reconstruction method which utilizes a median root prior (MRP). The method favours images which have locally monotonous radioactivity concentrations. The new reconstruction algorithm was applied to ideal simulated data, phantom data and some patient examinations with PET. The same projection data were reconstructed with filtered back-projection (FBP) and maximum likelihood-expectation maximization (ML-EM) methods for comparison. The MRP method provided good-quality images with a similar resolution to the FBP method with a ramp filter, and at the same time the noise properties were as good as with Hann-filtered FBP images. The typical artefacts seen in FBP reconstructed images outside of the object were completely removed, as was the grainy noise inside the object. Quantitatively, the resulting average regional radioactivity concentrations in a large region of interest in images produced by the MRP method corresponded to the FBP and ML-EM results but at the pixel by pixel level the MRP method proved to be the most accurate of the tested methods. In contrast to other iterative reconstruction methods, e.g. ML-EM, the MRP method was not sensitive to the number of iterations nor to the adjustment of reconstruction parameters. Only the Bayesian parameter had to be set. The proposed MRP method is much more simple to calculate than the methods described previously, both with regard to the parameter settings and in terms of general use. The new MRP reconstruction method was shown to produce high-quality quantitative emission images with only one parameter setting in addition to the number of iterations.     

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.     

Attenuation-corrected 99mTc-MIBI SPECT in overweight patients with chronic ischaemic dysfunction: a comparison to NH3 PET and implications for the diagnosis of myocardial viability

OBJECTIVE: We determined the value of attenuation correction (AC) of myocardial perfusion estimation with (99m)Tc-MIBI SPECT in overweight patients by comparison of uncorrected (filtered back-projection (FBP) and corrected (an iterative algorithm with a measured attenuation coefficients map (FL-AC)) (99m)Tc-MIBI relative uptake to perfusion data obtained in the same patients with NH3 PET. In addition, the impact of attenuation correction for the assessment of myocardial viability with (99m)Tc-MIBI SPECT was determined using FDG PET as the reference method. METHODS: Thirty consecutive overweight patients (BMI=28+/-4) with left ventricular dysfunction underwent a resting (99m)Tc-MIBI SPECT and a PET study (NH3 and FDG). (99m)Tc-MIBI SPECT scans were reconstructed without attenuation correction (FBP) and with attenuation correction (FL-AC). The left ventricle was divided into 16 segments, in which the relative uptake was quantified using circumferential profiles. A relative uptake > or = 60% was considered consistent with viable myocardium for FDG and MIBI. RESULTS: The absolute difference between (99m)Tc-MIBI SPECT and NH3 PET uptakes was less pronounced in the inferior (12+/-10% vs. 17+/-12%, P<0.001), anteroseptal (12+/-11% vs. 16+/-12%, P=0.009) and septal (15+/-12% vs. 18+/-14%, P=0.003) regions (FL-AC vs. FBP, respectively). The sensitivity of MIBI for diagnosing myocardial viability increased from 83 to 100% (P=0.034), without loss in specificity. CONCLUSION: Attenuation correction improves myocardial perfusion estimation by (99m)Tc-MIBI SPECT in the inferior, anteroseptal and septal regions and increases its sensitivity for the diagnosis of myocardial viability.     

Image reconstruction using filtered backprojection and iterative method: effect on motion artifacts in myocardial perfusion SPECT

Patient motion during myocardial perfusion SPECT is a common source of errors. The extent and severity of motion artifacts have been described for filtered backprojection (FBP) reconstruction. In recent years, iterative reconstruction has been used increasingly in reconstruction of myocardial perfusion SPECT images and has been shown to be more accurate than FBP even in cases of incomplete datasets. This study evaluated the effect of iterative reconstruction on the extent and severity of motion artifacts. METHODS: Six normal, motion-free, and nongated (99m)Tc myocardial perfusion SPECT scans were selected, and simulated motion of 3 pixels was applied to the early, middle, and late phases of acquisition in 2 types of movement, returning and nonreturning. The images were acquired by a single-head gamma-camera in 32 steps at 30 s per step and in a 180 degrees arc from right anterior oblique to left posterior oblique. All original and shifted images were reconstructed using FBP and ordered-subset expectation maximization (OSEM) techniques and interpreted by 2 nuclear medicine specialists qualitatively and semiquantitatively (using 17 segments and a 5-point scoring system). RESULTS: Overall, 68.1% and 70.8% of shifted images were categorized as definitely abnormal in the FBP and OSEM reconstructions, respectively (P > 0.5). The mean summed score was 11.9 (+/-5.7) and 11.3 (+/-5.2) for nonreturning shifted images (P = 0.13) and 5.2 (+/-2.4) and 3.9 (+/-2.0) for returning shifted images (P < 0.001) in the OSEM and FBP reconstructions, respectively. The incidence of defects in different myocardial segments was similar with the 2 reconstruction methods. The summed score was higher with shifting in the middle phase of acquisition than in the late or early phase. CONCLUSION: Our study showed that the incidence of abnormal findings and the location of defects were not different between the 2 reconstruction types; however, with semiquantitative assessment, the severity of defects increased with OSEM reconstruction. Although OSEM reconstruction has been reported to be more tolerant to missing data than is FBP reconstruction, our study showed that OSEM reconstruction may be less tolerant to motion artifacts than is FBP reconstruction.     

Effect of reconstruction algorithms on myocardial blood flow measurement with 13N-ammonia PET.

Filtered backprojection (FBP) is the traditional method for 13N-NH3 PET studies. Ordered-subsets expectation maximization (OSEM) is popular for PET studies because of better noise properties. Scant data exist on the effect of reconstruction algorithms on quantitative myocardial blood flow (MBF) estimation. METHODS: Twenty patients underwent dynamic acquisition rest/stress 13N-NH3 studies. In Part 1, 19 rest/stress image pairs were reconstructed by FBP (10-mm Hanning filter) and by OSEM with 28 subsets and 2 (OSEM2), 6 (OSEM6), or 8 iterations (OSEM8), and a 10-mm postreconstruction smoothing gaussian filter. In Part 2, 9 image pairs were reconstructed by FBP (10-mm Hanning filter) and by OSEM with 28 subsets, 8 iterations, and a gaussian 5-, 10-, or 15-mm postreconstruction smoothing filter. Average MBF (mL/min/mL of myocardium) was calculated using a 3-compartment model. RESULTS: Part 1: For rest MBF, the correlations between FBP and each of the OSEM algorithms were r2 = 0.71, 0.73, and 0.77, respectively. MBF by OSEM6 (0.98 +/- 0.48 [mean +/- SD]) and OSEM8 (0.96 +/- 0.46) was not significantly different from FBP (1.02 +/- 0.39), but OSEM2 (0.80 +/- 0.37) was significantly lower (P < 0.0003). With stress, the correlations were high between FBP and OSEM6 and OSEM8 (r2 = 0.85 and 0.90), and MBF by OSEM6 and OSEM8 was not significantly different from FBP. Part 2: Resting MBF correlated well between FBP and all OSEM smoothing filters (r2 = 0.82, 0.85, and 0.88). Rest MBF using postsmoothing 5- or 10-mm filters was not different from FBP but was significantly lower with the 15-mm filter (P < 0.05). With stress, the correlations were good between FBP and OSEM regardless of smoothing (r2 = 0.76, 0.77, and 0.79). However, MBF with postsmoothing 10- and 15-mm filters was significantly lower than by FBP (P < 0.05). CONCLUSION: Reconstruction algorithms significantly affect the estimation of quantitative blood flow data and should not be assumed to be interchangeable. Although aggressive smoothing may produce visually appealing images with reduced noise levels, it may cause an underestimation of absolute quantitative MBF. In selecting a reconstruction algorithm, an optimal balance between noise properties and diagnostic accuracy must be emphasized.     

Effects of iterative reconstruction on image contrast and lesion detection in gamma camera coincidence imaging in lung and breast cancers.

To investigate the effects of iterative reconstruction in 18F-fluorodeoxyglucose (FDG) gamma camera coincidence imaging (GCI), image contrast and visual detection obtained by using the iterative ordered-subsets expectation maximization (OSEM) reconstruction, in a phantom and in patients with lung cancer and breast cancer, were compared with those obtained by using the conventional filtered backprojection (FBP) reconstruction. Images of a cylindrical phantom containing hot spheres of various sizes (10-38 mm) were acquired by positron emission tomography (PET) and GCI at various sphere-to-background activity ratios. Forty-one consecutive patients with biopsy-proven cancer of lung (n = 20) and breast (n = 21) underwent PET and GCI on the same day after intravenous injection of 370 MBq of FDG. GCI images reconstructed by the OSEM and the FBP were compared. FDG PET was considered as the standard of reference. In GCI phantom images, OSEM yielded better contrast and signal-to-noise ratio (SNR) than FBP over the range of sphere sizes. Attenuation correction improved both the image measures and sphere detection obtained by the OSEM in GCI. In the study involving patients, FDG PET depicted 41 primary tumours and 25 metastatic lymph nodes. All of the tumours >2 cm in diameter (n = 25), six of the nine tumours 1.5-2.0 cm in diameter (67%), two of seven tumours <1.5 cm in diameter (29%), and 20 metastatic lymph nodes (80%) were detected in attenuation uncorrected GCI reconstructed by the OSEM as well as the FBP. The undetected lesions in GCI were identical between the OSEM and the FBP reconstructions. OSEM yielded significantly greater tumour-to-background (T/B) ratios and lower noise than FBP in GCI (T/B ratios, 4.1+/-3.2 vs 3.7+/-2.7, P = 0.02; noise, 0.09+/-0.04 vs 0.14+/-0.05, P<0.0001). In conclusion, OSEM yielded better image contrast and less noise than the FBP in GCI, but the lesion detection obtained by the OSEM and the FBP in attenuation uncorrected GCI in patients with lung cancer and breast cancer were similar. Phantom data suggest the potential of OSEM for improving lesion detection in GCI after attenuation correction.     

Quantification of regional myocardial blood flow using dynamic H2(15)O PET and factor analysis.

Because the use of factor analysis has been proposed for extracting pure physiologic temporal or spatial information from dynamic nuclear medicine images, factor analysis should be capable of robustly estimating regional myocardial blood flow (rMBF) using H2(15)O PET without additional C15O PET, which is a cumbersome procedure for patients. Therefore, we measured rMBF using time-activity curves (TACs) obtained from factor analysis of dynamic myocardial H2(15)O PET images without the aid of C15O PET. METHODS: H2(15)O PET of six healthy dogs at rest and during stress was performed simultaneously with microsphere studies using 85Sr, 46Sc, and 113SN: We performed factor analysis in two steps after reorienting and masking the images to include only the cardiac region. The first step discriminated each factor in the spatial distribution and acquired the input functions, and the second step extracted regional-tissue TACS: Image-derived input functions obtained by factor analysis were compared with those obtained by the sampling method. rMBF calculated using a compartmental model with tissue TACs from the second step of the factor analysis was compared with rMBF measured by microsphere studies. RESULTS: Factor analysis was successful for all the dynamic H2(15)O PET images. The input functions obtained by factor analysis were nearly equal to those obtained by arterial blood sampling, except for the expected delay. The correlation between rMBF obtained by factor analysis and rMBF obtained by microsphere studies was good (r = 0.95). The correlation between rMBF obtained by the region-of-interest method and rMBF obtained by microsphere studies was also good (r = 0.93). CONCLUSION: rMBF can be measured robustly by factor analysis using dynamic myocardial H2(15)O PET images without additional C15O blood-pool PET.     

Postinjection transmission scanning in myocardial 18F-FDG PET studies using both filtered backprojection and iterative reconstruction.

The aim of the present study was to evaluate the effect of postinjection transmission scanning (Post-Tx) on both the qualitative interpretation and the quantitative analysis of cardiac (18)F-FDG PET images. Furthermore, the accuracy of 2 different methods to correct for emission contamination was studied. An additional aim of this study was to compare images reconstructed with both standard filtered backprojection (FBP) and an iterative reconstruction algorithm (ordered-subset maximization expectation [OSEM]). METHODS: Sixteen patients underwent dynamic (18)F-FDG imaging. Both before injection of (18)F-FDG and after completing the emission scan, a 10-min transmission scan was performed (Pre-Tx and Post-Tx, respectively). Images were reconstructed using both FBP and OSEM. The emission study reconstructed with Pre-Tx was considered to be the gold standard. Emission studies were also reconstructed with Post-Tx, with and without correction for emission contamination. Correction for emission contamination was performed with either transmission image segmentation (TIS) or by estimating the emission bias from the last emission frame (dwell profile [DP] method). All images were then compared by calculating ratios of (18)F-FDG activity between corresponding myocardial segments in each patient. Furthermore, qualitative grading of (18)F-FDG uptake was compared between the studies. RESULTS: The mean ratio of (18)F-FDG activity between segments from FBP-Post and FBP-Pre was 0.78 +/- 0.08. When TIS and DP were used, the mean ratios were 0.80 +/- 0.07 and 0.94 +/- 0.06, respectively. The use of OSEM resulted in, on average, 2% lower values for (18)F-FDG activity as compared with FBP. The mean normalized (18)F-FDG uptake was higher in FBP-Post, especially in segments with decreased (18)F-FDG activity. Only in the case of DP were no significant differences observed as compared with FBP-Pre. In general, qualitative analysis of the images showed that the agreement between the reconstruction methods was comparable with the reproducibility of FBP-Pre. CONCLUSION: Post-Tx for attenuation correction in cardiac (18)F-FDG PET scans resulted in substantial underestimation of (18)F-FDG activity. More accurate results were obtained with correction for emission contamination using DP. Differences in visual assessment of (18)F-FDG images were small. Finally, iterative reconstruction could be used as an alternative to FBP in static (18)F-FDG imaging of the heart.     

Qualitative and quantitative comparison between images obtained with filtered back projection and iterative reconstruction in prostate cancer lesions of (18)F-FDG PET.

BACKGROUND: Recently, iterative reconstruction with segmented attenuation corrections (IRSAC) has been introduced for reconstruction of (18)F-FDG PET images. IRSAC produces images that are more pleasing to the eye, but qualitative and quantitative comparisons between IRSAC and filtered back projection (FBP) have not been reported for metastatic cancer. Since quantitative data has been widely used as an adjunct to interpretation of PET scans, comparison between IRSAC and FBP is needed. The purpose of this study was to compare image quality and the maximum standardized uptake value (SUVmax) obtained with FBP and with IRSAC in metastatic lesions from prostate cancer. METHODS: Twenty (18)F-FDG PET scans (10 baseline and 10 follow-up) were performed in 10 patients with prostate cancer (ages 66-85 yrs, mean 73.6 yrs). Acquisition began 45 min after injection of 370 MBq of (18)F-FDG. Images were reconstructed using FBP and IRSAC, and submitted to visual and quantitative analysis. SUVmax was obtained for all metastases, on FBP and IRSAC. A Jaszczak phantom study was also performed. RESULTS: IRSAC images showed better image quality than FBP especially in regions of high activity concentrations. IRSAC detected 106 lesions on both baseline and follow-up scans, while FBP detected 100 and 95 lesions on baseline and follow-up scans, respectively. Therefore, 17 more lesions were seen on IRSAC. The mean SUVmax values on baseline scans for FBP and IRSAC were systematically different, at 4.46+/-1.99 and 5.13+/-2.67, respectively. On follow-up scans values were 3.89+/-1.72 for FBP and 4.29+/-1.93 for IRSAC. Comparison of FBP with IRSAC on baseline and follow-up scans were statistically significant (baseline: paired "t"-test p=0.0017; follow-up: paired "t"-test p=0.0008). Phantom studies reveal that these differences can be explained by the type of reconstruction filters used, and IRSAC was more accurate than FBP. CONCLUSIONS: IRSAC detects smaller volumes in phantoms, patient images are easier to interpret and more metastatic lesions were detected. In addition, IRSAC provides reproducible quantitative data, comparable to data provided by FBP. IRSAC SUV and FBP SUV are in close agreement but there was a statistically significant difference between the two, and therefore threshold values of SUV will probably need to be re-determined with IRSAC, and are likely to be 10 to 19% higher than currently reported.     

The significance of a dipyridamole induced 99mTc-MIBI perfusion abnormality on single photon emission tomography: a quantitative validation with labelled water and positron emission tomography.

To relate technetium-99m 2-methoxy-isobutyl-isonitrile (99mTc-MIBI) uptake to regional myocardial blood flow (rMBF), 99mTc-MIBI single photon emission tomography (SPET) and H2(15)O positron emission tomography (PET) scans were obtained at rest and after dipyridamole infusion in six patients with single vessel coronary artery disease. 99mTc-MIBI and H2(15)O data sets were created for each segment perfused by the stenotic vessel and for a normal reference area, assigning regions on the SPET tomograms to comparable regions on the PET by similar transaxial image reconstructions. All patients demonstrated post-dipyridamole 99mTc-MIBI perfusion defects in the territories supplied by the stenotic arteries. Resting rMBF in these regions was slightly lower than that in the normal areas (0.82 +/- 0.05 vs 0.90 +/- 0.09 ml/g/min, P = NS). A 43% +/- 14% reduction in 99mTc-MIBI activity in the area at risk was coupled with on average a 60% +/- 9% reduction in post-dipyridamole rMBF compared with control regions (0.98 +/- 0.08 vs 2.52 +/- 0.51 ml/g/min, P < 0.001). Thus, SPET assessment of 99mTc-MIBI uptake tends to underestimate the perfusion contrast between areas with normal and areas with low coronary vasodilatory reserve when compared to PET. However, these findings may still not affect the clinical usefulness of 99mTc-MIBI and more extensive studies are required to confirm these results in the clinical environment.     

Value of iterative reconstruction, attenuation correction, and image fusion in the interpretation of FDG PET images with an integrated dual-head coincidence camera and X-ray-based attenuation maps

PURPOSE: To compare lesion detectability on 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomographic (PET) images obtained with a dual-head coincidence (DHC) gamma camera equipped with an integrated x-ray tube-based transmission system (a) with images reconstructed with filtered back projection (FBP) and those reconstructed with an iterative reconstruction algorithm based on coincidence-ordered subsets expectation maximization (COSEM), (b) with images reconstructed without and with attenuation correction (AC), and (c) with images reconstructed without and with image fusion for anatomic mapping. MATERIALS AND METHODS: Thirty-five patients known or suspected to have malignancy underwent initial imaging with a dedicated positron emission tomography (PET) unit after injection of 10 mCi (370 MBq) of FDG. Transmission computed tomographic (CT) scans and FDG emission images were then obtained with the DHC camera. The proportion of lesions detected on the various sets of FDG DHC images was determined by using FDG PET as the standard of reference. Imaging findings were correlated with those from histologic examination and clinical follow-up, in consultation with the respective referring physicians. RESULTS: FDG PET depicted 78 lesions, 29 of which were equal to or less than 1.5 cm in diameter. FDG DHC depicted 52 of the 78 (67%), 59 of 78 (76%), and 61 of the 78 (78%) lesions, respectively, when image reconstruction was performed with FBP without AC, COSEM without AC, and both COSEM and AC. The detection rate of lesions 1.5 cm or smaller was better with COSEM and AC than with FBP (55% vs 34%, respectively). In addition, COSEM and AC allowed more confidence in the interpretation. None of these differences, however, were significant. Fusion of CT scans and FDG DHC images obtained with COSEM and AC allowed localization of lesions to the skeleton in three patients and to the liver versus adjacent bowel in three patients. Image fusion was especially helpful for localizing lesions in the neck in five patients. Anatomic mapping on fusion images was clinically relevant in 11 patients (31%). CONCLUSION: The COSEM reconstruction algorithm should replace FBP when available. Functional anatomic mapping improved lesion localization in one-third of the patients studied.     

Comparison of the extent of delayed-enhancement cardiac magnetic resonance imaging with and without phase-sensitive reconstruction at 3.0 T

OBJECTIVES: To evaluate phase-sensitive reconstructed images versus magnitude images generated by an inversion recovery pulse sequence for the determination of myocardial infarct size in delayed-enhancement cardiac magnetic resonance (DE-CMR) at 3 T. MATERIALS AND METHODS: Thirty patients were examined at 3 T and DE images were obtained 10 minutes after contrast agent administration using a phase-sensitive breath-hold segmented inversion recovery gradient echo sequence. From magnitude and phase images, the percentage of hyperenhanced myocardium was expressed. Contrast-to-noise ratio (CNR) measurements were performed in hyperenhanced and normal myocardium. RESULTS: We observed excellent correlation and concordance between hyperenhanced myocardium determined on phase-sensitive reconstructed and magnitude images. The mean CNR values were significantly higher in phase-sensitive reconstructed images compared with magnitude images (10.5 +/- 5.4 vs. 6.1 +/- 4.8; P < 0.001). CONCLUSIONS: DE-CMR with phase-sensitive reconstruction at 3.0 T provides similar results to magnitude images, but with a significantly greater CNR between infarcted and normal myocardium.     

FBP和OSEM对正常人脑内多巴胺转运体分布半定量值影响的研究

目的 研究不同PET重建方法对正常人脑内多巴胺转运体（DAT）分布半定量值的影响。方法 将2014年3月至2015年6月期间41例健康受试者（正常人）的11C-甲基-N-2β-甲基酯-3β-（4-氟-苯基）托烷（11C-CFT）PET图像分别进行滤波反投影法（FBP）和有序子集最大期望值迭代法（OSEM）重建,自动勾画尾状核、壳核前部和后部等感兴趣脑区,以缺乏DAT分布的顶枕皮质作为参考区,按公式计算DAT分布的半定量值。DAT分布半定量值的组间比较采用配对t检验,相关性分析采用Pearson相关分析法。结果 基于OSEM重建的PET图像中DAT分布半定量值分别为:尾状核（1.77~2.15）、壳核前部（2.17~2.39）、壳核后部（1.71~2.06）;基于FBP重建的PET图像中DAT分布半定量值分别为:尾状核（1.68~2.10）、壳核前部（2.07~2.37）、壳核后部（1.62~1.96）。基于OSEM重建的PET图像中双侧尾状核、壳核前部及后部的DAT分布半定量值均显著高于基于FBP重建的PET图像,且两者间的差异均有统计学意义（t=9.658~15.859,均P=0.000）。Pearson相关性分析结果显示,基于OSEM与FBP重建的PET图像的DAT分布半定量值在双侧尾状核、壳核前部及后部均呈显著正相关（R2=0.907~0.951,均P=0.000）。基于OSEM与FBP重建的PET图像中双侧尾状核、壳核前部及后部DAT分布半定量值均呈现随年龄增长逐渐减低的趋势。结论 不同PET重建方法获得的正常人脑内DAT分布半定量值存在显著差异,在多中心或纵向研究中需要保持PET图像重建方法的一致性。     

Implementation and evaluation of an ordered subsets reconstruction algorithm for transmission PET studies using median root prior and inter-update median filtering

An ordered subsets (OS) reconstruction algorithm based on the median root prior (MRP) and inter-update median filtering was implemented for the reconstruction of low count statistics transmission (TR) scans. The OS-MRP-TR algorithm was evaluated using an experimental phantom, simulating positron emission tomography (PET) whole-body (WB) studies, as well as patient data. Various experimental conditions, in terms of TR scan time (from 1 h to 1 min), covering a wide range of TR count statistics were evaluated. The performance of the algorithm was assessed by comparing the mean value of the attenuation coefficient (MVAC) of known tissue types and the coefficient of variation (CV) for low-count TR images, reconstructed with the OS-MRP-TR algorithm, with reference values obtained from high-count TR images reconstructed with a filtered back-projection (FBP) algorithm. The reconstructed OS-MRP-TR images were then used for attenuation correction of the corresponding emission (EM) data. EM images reconstructed with attenuation correction generated by OS-MRP-TR images, of low count statistics, were compared with the EM images corrected for attenuation using reference (high statistics) TR data. In all the experimental situations considered, the OS-MRP-TR algorithm showed: (1) a tendency towards a stable solution in terms of MVAC; (2) a difference in the MVAC of within 5% for a TR scan of 1 min reconstructed with the OS-MRP-TR and a TR scan of 1 h reconstructed with the FBP algorithm; (3) effectiveness in noise reduction, particularly for low count statistics data [using a specific parameter configuration the TR images reconstructed with OS-MRP-TR(1 min) had a lower CV than the corresponding TR images of a 1-h scan reconstructed with the FBP algorithm]; (4) a difference of within 3% between the mean counts in the EM images attenuation corrected using the OS-MRP-TR images of 1 min and the mean counts in the EM images attenuation corrected using the OS-MRP-TR images of 1 h; (5) preservation of "good" image quality for both TR and EM reconstructed images. In conclusion, the OS-MRP-TR algorithm is particularly suitable for WB PET studies, allowing: (1) the acquisition of a very short TR scan (within 1 min), (2) the reconstruction of such TR data in low-noise TR images and (3) the use of the reconstructed OS-MRP-TR images for attenuation correction of corresponding EM data.     

A new iterative reconstruction technique for attenuation correction in high-resolution positron emission tomography

A new iterative reconstruction technique (NIRT) for positron emission computed tomography (PET), which uses transmission data for nonuniform attenuation correction, is described. Utilizing the general inverse problem theory, a cost functional which includes a noise term was derived. The cost functional was minimized using a weighted-least-square maximum a posteriori conjugate gradient (CG) method. The procedure involves a change in the Hessian of the cost function by adding an additional term. Two phantoms were used in a real data acquisition. The first was a cylinder phantom filled with uniformly distributed activity of 74 MBq of fluorine-18. Two different inserts were placed in the phantom. The second was a Hoffman brain phantom filled with uniformly distributed activity of 7.4 MBq of¹⁸F. Resulting reconstructed images were used to test and compare a new iterative reconstruction technique with a standard filtered backprojection (FBP) method. The results confirmed that NIRT, based on the conjugate gradient method, converges rapidly and provides good reconstructed images. In comparison with standard results obtained by the FBP method, the images reconstructed by NIRT showed better noise properties. The noise was measured as rms% noise and was less, by a factor of 1.75, in images reconstructed by NIRT than in the same images reconstructed by FBP. The distance between the Hoffman brain slice reconstructed by FBP and the perfect PET Hoffman brain slice created from the MRI image was 0.526, while the same distance for the Hoffman brain slice reconstructed by NIRT was 0.328. The NIRT method suppressed the propagation of the noise without visible loss of resolution in the reconstructed PET images.     

A trial for the quantification of regional myocardial blood flow with continuous infusion of Tc-99m MIBI and dynamic SPECT

We propose a new method to quantify regional myocardial blood flow (rMBF) by continuous infusion of Tc-99m MIBI and dynamic SPECT. METHODS: Five patients with old myocardial infarction were studied. During continuous infusion of MIBI (approximately 740 MBq) with a syringe pump in 10 min, dynamic SPECT scan was performed every minute and lasted 20 min after the start of infusion to identify myocardial uptake of MIBI. Input function was obtained from the radioactivity in the left ventricle (LV) in dynamic SPECT images. Spillover fraction between LV and myocardium (M) was corrected with phantom data. The influx constant (Ku) was calculated by Patlak plot graphical analysis, and compared with rMBF measured by PET (F) with N-13 ammonia based on Patlak plot analysis with correction for the extraction fraction. To correct the limited first-pass extraction of MIBI, linearization correction by means of the permeability-surface area (PS) product value was also applied. RESULTS: Spillover fractions of MIBI were 0.169+/-0.056 from LV to M, and 0.042+/-0.021 from M to LV. Ku was well correlated with F (Ku = 0.057 + 0.220F, r = 0.83, p < 0.01) and the slope and correlation were improved after linearizaiton (F(MIBI) = -0.131+0.858F, r = 0.94, p < 0.01). CONCLUSION: The proposed method has the potential to be a clinically feasible tool for quantitative measurement of rMBF.     

ROC and localization ROC analyses of lesion detection in whole-body FDG PET: effects of acquisition mode, attenuation correction and reconstruction algorithm.

Receiver operating characteristic (ROC) and localization ROC (LROC) studies were performed to compare lesion detection at the borderline of detectability on images reconstructed with two-dimensional filtered backprojection (FBP) without attenuation correction (a common clinical protocol), three-dimensional FBP without attenuation correction, two-dimensional FBP with segmented attenuation correction and a two-dimensional iterative maximum a posteriori (MAP) algorithm using attenuation correction. Lung cancer was the model for the study because of the prominent role of 18F-fluorodeoxyglucose PET in the staging of lung cancer and the importance of lesion detection for staging. METHODS: Simulated lung cancer lesions were added to two-dimensional and three-dimensional PET data from healthy volunteers. Data were reconstructed using the four methods. Four nuclear medicine physicians evaluated the images. Detection performance with each method was compared using ROC and LROC analysis. Jackknife analysis provided estimates of statistical significance for differences across all readers for the ROC results. RESULTS: ROC and LROC results indicated statistically significant degradation in detection performance with three-dimensional acquisition (average area under ROC curves [Az] 0.51; average area under LROC curves [A(z,LROC)] 0.13) and segmented attenuation correction (average Az 0.59; average Az,LROC 0.29) compared with two-dimensional FBP without attenuation correction (average Az 0.79; average A(z,LROC) 0.54). ROC and LROC results indicated an improvement in detection performance with iterative MAP reconstruction (average Az 0.83; average A(z,LROC) 0.64) compared with two-dimensional FBP reconstruction; this improvement was not statistically significant. CONCLUSION: Use of segmented attenuation correction or three-dimensional acquisition with FBP reconstruction is not expected to improve detection of lung lesions on whole-body PET images compared with images with two-dimensional FBP without attenuation correction. The potential improvement in detection obtained with an iterative MAP reconstruction method is small compared with that obtained with two-dimensional FBP without attenuation correction.