Diagnostic value of regional myocardial flow reserve measurements using Rubidium-82 PET : Disclosures none.

PURPOSE: Visual assessment of Rubidium (Rb-82) PET myocardial perfusion images is usually combined with global myocardial flow reserve (MFR) measurements. However, small regional blood flow deficits may go unnoticed. Our aim was to compare the diagnostic value of regional with global MFR in the detection of obstructive coronary artery disease (oCAD). METHODS: We retrospectively included 1519 patients referred for rest and regadenoson-induced stress Rb-82 PET/CT without prior history of oCAD. MFR was determined globally, per vessel territory and per myocardial segment and compared using receiver-operating characteristic analysis. Vessel MFR was defined as the lowest MFR of the coronary territories and segmental MFR as the lowest MFR of the 17-segments. The primary endpoint was oCAD on invasive coronary angiography. RESULTS: The 148 patients classified as having oCAD had a lower global MFR (median 1.9, interquartile range [1.5-2.4] vs. 2.4 [2.0-2.9]), lower vessel MFR (1.6 [1.2-2.1] vs. 2.2 [1.9-2.6]) and lower segmental MFR (1.3 [ 0.9-1.6] vs. 1.8 [1.5-2.2]) as compared to the non-oCAD patients (p < 0.001). The area under the curve for segmental MFR (0.81) was larger (p ≤ 0.005) than of global MFR (0.74) and vessel MFR (0.78). CONCLUSIONS: The use of regional MFR instead of global MFR is recommended as it improves the diagnostic value of Rb-82 PET in the detection of oCAD.

Performance of digital PET/CT compared with conventional PET/CT in oncologic patients: a prospective comparison study.

PURPOSE: Digital PET systems (dPET) improve lesion detectability as compared to PET systems with conventional photomultiplier tubes (cPET). We prospectively studied the performance of high-resolution digital PET scans in patients with cancer, as compared with high- and standard-resolution conventional PET scans, taking the acquisition order into account. METHODS: We included 212 patients with cancer, who were referred for disease staging or restaging. All patients underwent FDG-PET/CT on a dPET scanner and on a cPET scanner in a randomized order. The scans were acquired immediately after each other. Three image reconstructions were generated: 1) standard-resolution (4 × 4 × 4 mm3 voxels) cPET, 2) high-resolution (2 × 2 × 2 mm3 voxels) cPET, and 3) high-resolution dPET. Two experienced PET readers visually assessed the three reconstructions side-by-side and ranked them according to scan preference, in an independent and blinded fashion. RESULTS: On high-resolution dPET, the PET readers detected more lesions or they had a higher diagnostic confidence than on high- and standard-resolution cPET (p < 0.001). High-resolution dPET was preferred in 90% of the cases, as compared to 44% for high-resolution cPET and 1% for standard-resolution cPET (p < 0.001). However, for the subgroup of patients where dPET was made first (n = 103, 61 ± 10 min after FDG administration) and cPET was made second (93 ± 15 min after FDG administration), no significant difference in preference was found between the high-resolution cPET and dPET reconstructions (p = 0.41). CONCLUSIONS: DPET scanners in combination with high-resolution reconstructions clinically outperform cPET scanners with both high- and standard-resolution reconstructions as the PET readers identified more FDG-avid lesions, their diagnostic confidence was increased, and they visually preferred dPET. However, when dPET was made first, high-resolution dPET and high-resolution cPET showed similar performance, indicating the positive effect of a prolonged FDG uptake time. Therefore, high-resolution cPET in combination with a prolonged FDG uptake time can be considered as an alternative.

Performance of Digital PET Compared with High-Resolution Conventional PET in Patients with Cancer.

Recently introduced PET systems using silicon photomultipliers with digital readout (dPET) have an improved timing and spatial resolution, aiming at a better image quality than conventional PET (cPET) systems. We prospectively evaluated the performance of a dPET system in patients with cancer, as compared with high-resolution (HR) cPET imaging. Methods: After a single 18F-FDG injection, 66 patients underwent dPET and cPET imaging in randomized order. We used HR reconstructions (2 × 2 × 2 mm voxels) for both scanners and determined SUVmax, SUVmean, lesion-to-background ratio (LBR), metabolic tumor volume (MTV), and lesion diameter in up to 5 18F-FDG-positive lesions per patient. Furthermore, we counted the number of visible and measurable lesions on each PET scan. Two nuclear medicine specialists determined, in a masked manner, the TNM score from both image sets in 30 patients referred for initial staging. For all 66 patients, these specialists separately evaluated image quality (4-point scale) and determined the scan preference. Results: We included 238 lesions that were visible and measurable on both PET scans. For 27 patients, we found 37 additional lesions on dPET (41%) that were unmeasurable (n = 14) or invisible (n = 23) on cPET. Mean (±SD) SUVmean, SUVmax, LBR, and MTV on cPET were 5.2 ± 3.9, 6.9 ± 5.6, 5.0 ± 3.6, and 2,991 ± 13,251 mm3, respectively. On dPET, SUVmean, SUVmax, and LBR increased by 24%, 23%, and 27%, respectively (P < 0.001) whereas MTV decreased by 13% (P < 0.001), compared with cPET. Visual analysis showed TNM upstaging with dPET in 13% of the patients (4/30). dPET images also had higher scores for quality (P = 0.003) and were visually preferred in most cases (65%). Conclusion: dPET improved the detection of small lesions, upstaged the disease, and produced images that were visually preferred to those from HR cPET. More studies are necessary to confirm the superior diagnostic performance of dPET.Keywords: digital PET; conventional PET; FDG PET; lesion detection; cancer imaging.

SUV variability in EARL-accredited conventional and digital PET.

BACKGROUND: A high SUV-reproducibility is crucial when different PET scanners are in use. We evaluated the SUV variability in whole-body FDG-PET scans of patients with suspected or proven cancer using an EARL-accredited conventional and digital PET scanner. In a head-to-head comparison we studied images of 50 patients acquired on a conventional scanner (cPET, Ingenuity TF PET/CT, Philips) and compared them with images acquired on a digital scanner (dPET, Vereos PET/CT, Philips). The PET scanning order was randomised and EARL-compatible reconstructions were applied. We measured SUVmean, SUVpeak, SUVmax and lesion diameter in up to 5 FDG-positive lesions per patient. The relative difference ΔSUV between cPET and dPET was calculated for each SUV-parameter. Furthermore, we calculated repeatability coefficients, reflecting the 95% confidence interval of ΔSUV. RESULTS: We included 128 lesions with an average size of 19 ± 14 mm. Average ΔSUVs were 6-8% with dPET values being higher for all three SUV-parameters (p < 0.001). ΔSUVmax was significantly higher than ΔSUVmean (8% vs. 6%, p = 0.002) and than ΔSUVpeak (8% vs. 7%, p = 0.03). Repeatability coefficients across individual lesions were 27% (ΔSUVmean and ΔSUVpeak) and 33% (ΔSUVmax) (p < 0.001). CONCLUSIONS: With EARL-accredited conventional and digital PET, we found a limited SUV variability with average differences up to 8%. Furthermore, only a limited number of lesions showed a SUV difference of more than 30%. These findings indicate that EARL standardisation works. TRIAL REGISTRATION: This prospective study was registered on the 31th of October 2017 at ClinicalTrials.cov. URL: https://clinicaltrials.gov/ct2/show/NCT03457506?id=03457506&rank=1.

Multicentre quantitative 68Ga PET/CT performance harmonisation.

PURPOSE: Performance standards for quantitative 18F-FDG PET/CT studies are provided by the EANM Research Ltd. (EARL) to enable comparability of quantitative PET in multicentre studies. Yet, such specifications are not available for 68Ga. Therefore, our aim was to evaluate 68Ga-PET/CT quantification variability in a multicentre setting. METHODS: A survey across Dutch hospitals was performed to evaluate differences in clinical 68Ga PET/CT study protocols. 68Ga and 18F phantom acquisitions were performed by 8 centres with 13 different PET/CT systems according to EARL protocol. The cylindrical phantom and NEMA image quality (IQ) phantom were used to assess image noise and to identify recovery coefficients (RCs) for quantitative analysis. Both phantoms were used to evaluate cross-calibration between the PET/CT system and local dose calibrator. RESULTS: The survey across Dutch hospitals showed a large variation in clinical 68Ga PET/CT acquisition and reconstruction protocols. 68Ga PET/CT image noise was below 10%. Cross-calibration was within 10% deviation, except for one system to overestimate 18F and two systems to underestimate the 68Ga activity concentration. RC-curves for 18F and 68Ga were within and on the lower limit of current EARL standards, respectively. After correction for local 68Ga/18F cross-calibration, mean 68Ga performance was 5% below mean EARL performance specifications. CONCLUSIONS: 68Ga PET/CT quantification performs on the lower limits of the current EARL RC standards for 18F. Correction for local 68Ga/18F cross-calibration mismatch is advised, while maintaining the EARL reconstruction protocol thereby avoiding multiple EARL protocols.

Comparison of maximal Rubidium-82 activities for myocardial blood flow quantification between digital and conventional PET systems.

BACKGROUND: PET-based myocardial blood flow (MBF) quantification can be inaccurate when using high tracer activities. Our aim was to derive the maximal Rubidium-82 activity for MBF assessment using a new digital PET system and compare the results with conventional analog systems. METHODS: 1.8 GBq Rubidium-82 was injected into the cardiac insert of an anthropomorphic torso phantom. Data were acquired for 10 min using an Ingenuity TF (Philips Healthcare), Discovery 690 (D690, GE Healthcare), and digital PET prototype system (Philips Healthcare). The dynamic ranges, defined as the maximal measured activity in the reconstructed images deviating < 10% from the true present activity, were determined in all scans. RESULTS: The dynamic ranges were 312 MBq for Ingenuity TF, 650 MBq for D690, and 654 MBq for digital PET prototype. CONCLUSIONS: The maximal Rb-82 activity for MBF assessment using digital PET prototype is higher than that for its analog counterpart (Ingenuity TF), but seems comparable to the D690.

Minimal starting time of data reconstruction for qualitative myocardial perfusion rubidium-82 positron emission tomography imaging.

OBJECTIVE: Qualitative positron emission tomography (PET) myocardial perfusion imaging (MPI) scans are reconstructed with a delay after an injection of rubidium-82 (Rb) to ensure blood pool clearance and sufficient left ventricle to myocardium contrast. Our aim was to derive the minimal starting time of data reconstruction (STDR) after an injection of Rb for which the diagnostic value and image quality remained unaffected. MATERIALS AND METHODS: We retrospectively included 23 patients who underwent rest-stress Rb PET MPI using 740 MBq. Patients fulfilling one of the two criteria indicating a slow blood pool clearance (ejection fraction <50% and/or cardiac output <3 l/min) were included in a consecutive manner. PET images using five different STDRs (1:15-2:15 min) were reconstructed and compared with reference images (STDR of 2:30 min). Differences in the summed rest score greater than or equal to 3 and total perfusion deficit greater than 3% were considered to significantly influence the diagnostic value. In addition, image quality was scored by two experts as not interpretable, inferior, adequate, or excellent. RESULTS: The summed rest score differed greater than or equal to 3 from the reference in seven or more patients (≥30%) using STDR less than or equal to 2:00 min (P<0.02). STDR less than or equal to 1:30 min resulted in six or more patients (≥26%) with a total perfusion deficit difference greater than 3% (P<0.03).In addition, STDR less than or equal to 2:00 min resulted in a lower image quality (P<0.002) and STDR less than or equal to 2:15 min resulted in greater than or equal to two scans with noninterpretable image quality. CONCLUSION: STDR less than or equal to 2:15 min resulted in lower diagnostic value or insufficient image quality for qualitative PET MPI using 740 MBq Rb. An STDR of 2:30 min can be considered for clinical adoption.

Diagnostic implications of a small-voxel reconstruction for loco-regional lymph node characterization in breast cancer patients using FDG-PET/CT.

BACKGROUND: We evaluated the diagnostic implications of a small-voxel reconstruction for lymph node characterization in breast cancer patients, using state-of-the-art FDG-PET/CT. We included 69 FDG-PET/CT scans from breast cancer patients. PET data were reconstructed using standard 4 × 4 × 4 mm3 and small 2 × 2 × 2 mm3 voxels. Two hundred thirty loco-regional lymph nodes were included, of which 209 nodes were visualised on PET/CT. All nodes were visually scored as benign or malignant, and SUVmax and TBratio(=SUVmax/SUVbackground) were measured. Final diagnosis was based on histological or imaging information. We determined the accuracy, sensitivity and specificity for both reconstruction methods and calculated optimal cut-off values to distinguish benign from malignant nodes. RESULTS: Sixty-one benign and 169 malignant lymph nodes were included. Visual evaluation accuracy was 73% (sensitivity 67%, specificity 89%) on standard-voxel images and 77% (sensitivity 78%, specificity 74%) on small-voxel images (p = 0.13). Across malignant nodes visualised on PET/CT, the small-voxel score was more often correct compared with the standard-voxel score (89 vs. 76%, p <  0.001). In benign nodes, the standard-voxel score was more often correct (89 vs. 74%, p = 0.04). Quantitative data were based on the 61 benign and 148 malignant lymph nodes visualised on PET/CT. SUVs and TBratio were on average 3.0 and 1.6 times higher in malignant nodes compared to those in benign nodes (p <  0.001), on standard- and small-voxel PET images respectively. Small-voxel PET showed average increases in SUVmax and TBratio of typically 40% over standard-voxel PET. The optimal SUVmax cut-off using standard-voxels was 1.8 (sensitivity 81%, specificity 95%, accuracy 85%) while for small-voxels, the optimal SUVmax cut-off was 2.6 (sensitivity 78%, specificity 98%, accuracy 84%). Differences in accuracy were non-significant. CONCLUSIONS: Small-voxel PET/CT improves the sensitivity of visual lymph node characterization and provides a higher detection rate of malignant lymph nodes. However, small-voxel PET/CT also introduced more false-positive results in benign nodes. Across all nodes, differences in accuracy were non-significant. Quantitatively, small-voxel images require higher cut-off values. Readers have to adapt their reference standards.

Value of automatic patient motion detection and correction in myocardial perfusion imaging using a CZT-based SPECT camera.

BACKGROUND: Correction of motion has become feasible on cadmium-zinc-telluride (CZT)-based SPECT cameras during myocardial perfusion imaging (MPI). Our aim was to quantify the motion and to determine the value of automatic correction using commercially available software. METHODS AND RESULTS: We retrospectively included 83 consecutive patients who underwent stress-rest MPI CZT-SPECT and invasive fractional flow reserve (FFR) measurement. Eight-minute stress acquisitions were reformatted into 1.0- and 20-second bins to detect respiratory motion (RM) and patient motion (PM), respectively. RM and PM were quantified and scans were automatically corrected. Total perfusion deficit (TPD) and SPECT interpretation-normal, equivocal, or abnormal-were compared between the noncorrected and corrected scans. Scans with a changed SPECT interpretation were compared with FFR, the reference standard. Average RM was 2.5 ± 0.4 mm and maximal PM was 4.5 ± 1.3 mm. RM correction influenced the diagnostic outcomes in two patients based on TPD changes ≥7% and in nine patients based on changed visual interpretation. In only four of these patients, the changed SPECT interpretation corresponded with FFR measurements. Correction for PM did not influence the diagnostic outcomes. CONCLUSION: Respiratory motion and patient motion were small. Motion correction did not appear to improve the diagnostic outcome and, hence, the added value seems limited in MPI using CZT-based SPECT cameras.

Minimizing rubidium-82 tracer activity for relative PET myocardial perfusion imaging.

OBJECTIVES: Recommended rubidium-82 activities for relative myocardial perfusion imaging (MPI) using present-generation PET scanners may be unnecessarily high. Our aim was to derive the minimum activity for a reliable relative PET MPI assessment. MATERIALS AND METHODS: We analyzed 140 scans from 28 consecutive patients who underwent rest-stress MPI-PET (Ingenuity TF). Scans of 852, 682, 511, and 341 MBq were simulated from list-mode data and compared with a reference scan using 1023 MBq. Differences in the summed rest score, total perfusion deficit, and image quality were obtained between the reference and each of the simulated rest scans. Combined stress-rest scans obtained at a selected activity of 682 MBq were diagnostically interpreted by experts and outcome was compared with the reference scan interpretation. RESULTS: Differences in summed rest score more than or equal to 3 were found using 682, 511, and 341 MBq in two (7%), four (14%), and five (18%) patients, respectively. Differences in total perfusion deficit more than 7% were only found at 341 MBq in one patient. Image quality deteriorated significantly only for the 341 MBq scans (P<0.001). Interpretation of stress-rest scans did not differ between 682 and 1023 MBq scans. CONCLUSION: A significant reduction in administered Rb-82 activity is feasible in relative MPI. An activity of 682 MBq resulted in reliable diagnostic outcomes and image quality, and can therefore be considered for clinical adoption.

Quantification, improvement, and harmonization of small lesion detection with state-of-the-art PET.

In recent years, there have been multiple advances in positron emission tomography/computed tomography (PET/CT) that improve cancer imaging. The present generation of PET/CT scanners introduces new hardware, software, and acquisition methods. This review describes these new developments, which include time-of-flight (TOF), point-spread-function (PSF), maximum-a-posteriori (MAP) based reconstruction, smaller voxels, respiratory gating, metal artefact reduction, and administration of quadratic weight-dependent 18F-fluorodeoxyglucose (FDG) activity. Also, hardware developments such as continuous bed motion (CBM), (digital) solid-state photodetectors and combined PET and magnetic resonance (MR) systems are explained. These novel techniques have a significant impact on cancer imaging, as they result in better image quality, improved small lesion detectability, and more accurate quantification of radiopharmaceutical uptake. This influences cancer diagnosis and staging, as well as therapy response monitoring and radiotherapy planning. Finally, the possible impact of these developments on the European Association of Nuclear Medicine (EANM) guidelines and EANM Research Ltd. (EARL) accreditation for FDG-PET/CT tumor imaging is discussed.

Coronary artery calcification detection with invasive coronary angiography in comparison with unenhanced computed tomography.

OBJECTIVE: The presence of extensive coronary artery calcifications (CAC) influences treatment decisions, particularly for revascularization. However, important CAC might be missed with invasive coronary angiography (ICA). Our aim was to determine the accuracy of ICA in the identification of CAC using computed tomography (CT) as reference standard. PATIENTS AND METHODS: Overall, 349 consecutive patients who underwent both CT-based CAC-scoring and invasive coronary angiography within 60 days were retrospectively included. Two experienced operators classified CAC on ICA, without knowledge of CT-based CAC scoring, for each of the four main vessels as (0) absent, (1) mild, (2) moderate, or (3) dense calcifications. These scores were correlated with the CT-based Agatston CAC-scores, the noninvasive reference standard. The sensitivity, specificity, and accuracy of identified CAC using ICA were derived. Calcifications identified as moderate or dense on ICA or with a vessel-based Agatston score of more than 100 were considered important. RESULTS: CT classified 671 (48%) of the 1396 vessels as having moderately or densely calcified vessels (Agatston score >100), whereas this was 137 (9.8%) using ICA (P<0.001). A significant correlation was found between the CT-based and ICA-based CAC-scores for all vessels (P<0.001). The sensitivity in detecting any CAC by means of ICA was 43% with a specificity of 92% and an accuracy of 55%. The sensitivity of important CAC identification by ICA was 19%, the specificity 99%, and the accuracy 61%. CONCLUSION: The accuracy of ICA for the identification of calcifications is very low as only 19% of the relevant calcifications was identified. Preprocedural assessment of CAC with CT could be considered to improve the treatment approach.

Digital PET compliance to EARL accreditation specifications.

BACKGROUND: Our aim was to evaluate if a recently introduced TOF PET system with digital photon counting technology (Philips Healthcare), potentially providing an improved image quality over analogue systems, can fulfil EANM research Ltd (EARL) accreditation specifications for tumour imaging with FDG-PET/CT. FINDINGS: We have performed a phantom study on a digital TOF PET system using a NEMA NU2-2001 image quality phantom with six fillable spheres. Phantom preparation and PET/CT acquisition were performed according to the European Association of Nuclear Medicine (EANM) guidelines. We made list-mode ordered-subsets expectation maximization (OSEM) TOF PET reconstructions, with default settings, three voxel sizes (4 × 4 × 4 mm3, 2 × 2 × 2 mm3 and 1 × 1 × 1 mm3) and with/without point spread function (PSF) modelling. On each PET dataset, mean and maximum activity concentration recovery coefficients (RCmean and RCmax) were calculated for all phantom spheres and compared to EARL accreditation specifications. The RCs of the 4 × 4 × 4 mm3 voxel dataset without PSF modelling proved closest to EARL specifications. Next, we added a Gaussian post-smoothing filter with varying kernel widths of 1-7 mm. EARL specifications were fulfilled when using kernel widths of 2 to 4 mm. CONCLUSIONS: TOF PET using digital photon counting technology fulfils EARL accreditation specifications for FDG-PET/CT tumour imaging when using an OSEM reconstruction with 4 × 4 × 4 mm3 voxels, no PSF modelling and including a Gaussian post-smoothing filter of 2 to 4 mm.

Technical note: how to determine the FDG activity for tumour PET imaging that satisfies European guidelines.

BACKGROUND: For tumour imaging with PET, the literature proposes to administer a patient-specific FDG activity that depends quadratically on a patient's body weight. However, a practical approach on how to implement such a protocol in clinical practice is currently lacking. We aimed to provide a practical method to determine a FDG activity formula for whole-body PET examinations that satisfies both the EANM guidelines and this quadratic relation. RESULTS: We have developed a methodology that results in a formula describing the patient-specific FDG activity to administer. A PET study using the NEMA NU-2001 image quality phantom forms the basis of our method. This phantom needs to be filled with 2.0 and 20.0 kBq FDG/mL in the background and spheres, respectively. After a PET acquisition of 10 min, a reconstruction has to be performed that results in sphere recovery coefficients (RCs) that are within the specifications as defined by the EANM Research Ltd (EARL). By performing reconstructions based on shorter scan durations, the minimal scan time per bed position (T min) needs to be extracted using an image coefficient of variation (COV) of 15 %. At T min, the RCs should be within EARL specifications as well. Finally, the FDG activity (in MBq) to administer can be described by [Formula: see text] with c a constant that is typically 0.0533 (MBq/kg(2)), w the patient's body weight (in kg), and t the scan time per bed position that is chosen in a clinical setting (in seconds). We successfully demonstrated this methodology using a state-of-the-art PET/CT scanner. CONCLUSIONS: We provide a practical method that results in a formula describing the FDG activity to administer to individual patients for whole-body PET examinations, taking into account both the EANM guidelines and a quadratic relation between FDG activity and patient's body weight. This formula is generally applicable to any PET system, using a specified image reconstruction and scan time per bed position.

CT-based quantification of bone stock in large head metal-on-metal unilateral total hip replacements.

PURPOSE: To explore ipsilateral and contralateral acetabular roof bone stock density in unilateral large head MoM THA whether there is a significant lower acetabular bone stock in the hip with a metal-on-metal (MoM) total hip replacement compared to the contralateral side. Second part of this study is to examine if there are any associates with regard to potential bone stock density difference. MATERIALS & METHODS: A database of 317 patients with unilateral metal-on-metal (MoM) total hip replacements was set up retrospectively for this study. On computed tomography scans, conducted after a relative short in situ time period averaging 2.8 years, regions-of-interests were drawn in the trabecular bone of the acetabulum to measure average Hounsfield Units (HU). HU differences were calculated and tested by Wilcoxon signed-rank test. Univariate analysis was conducted to examine associates of potential bone loss. RESULTS: In a population of 317 patients (156 male, 161 female) with an average age of 61.9 ± 7.8, the median HU on the side of the MoM replacement was 123.3 (7.6-375.4). On the contralateral side, median HU was 144.7 (-0.4 to 332.8). The median HU difference was 21.4 after a mean post-operative in situ time of 2.8 years. The Wilcoxon signed-rank test proved a significant difference (p<0.001). Univariate analyses show that the in situ time of the MoM THA has a significant correlation with the bone density difference. CONCLUSION: Results show a significant lower bone density at the acetabular roof at the side of the prosthesis compared with the contralateral side after short in situ time of the MoM THA in patients with unilateral MoM total hip replacements. In our patient population, the in situ time showed a significant association with the acetabular bone density difference. As acetabular roof bone stock measurements are feasible and show temporal decline this could become an important parameter to be used in orthopedic decision making for revision surgery.

Current generation time-of-flight (18)F-FDG PET/CT provides higher SUVs for normal adrenal glands, while maintaining an accurate characterization of benign and malignant glands.

OBJECTIVE: Modern PET/CT scanners have significantly improved detectors and fast time-of-flight (TOF) performance and this may improve clinical performance. The aim of this study was to analyze the impact of a current generation TOF PET/CT scanner on standardized uptake values (SUV), lesion-background contrast and characterization of the adrenal glands in patients with suspected lung cancer, in comparison with literature data and commonly used SUV cut-off levels. METHODS: We included 149 adrenal glands from 88 patients with suspected lung cancer, who underwent (18)F-FDG PET/CT. We measured the SUVmax in the adrenal gland and compared this with liver SUVmean to calculate the adrenal-to-liver ratio (AL ratio). Results were compared with literature derived with older scanners, with SUVmax values of 1.0 and 1.8 for normal glands [1, 2]. Final diagnosis was based on histological proof or follow-up imaging. We proposed cut-off values for optimal separation of benign from malignant glands. RESULTS: In 127 benign and 22 malignant adrenal glands, SUVmax values were 2.3 ± 0.7 (mean ± SD) and 7.8 ± 3.2 respectively (p < 0.01). Corresponding AL ratios were 1.0 ± 0.3 and 3.5 ± 1.4 respectively (p < 0.01). With a SUVmax cut-off value of 3.7, 96% sensitivity and 96% specificity was reached. An AL ratio cut-off value of 1.8 resulted in 91% sensitivity and 97% specificity. The ability of both SUVmax and AL ratio to separate benign from malignant glands was similar (AUC 0.989 vs. 0.993, p = 0.22). CONCLUSIONS: Compared with literature based on the previous generation of PET scanners, current generation TOF (18)F-FDG PET/CT imaging provides higher SUVs for benign adrenal glands, while it maintains a highly accurate distinction between benign and malignant glands. Clinical implementation of current generation TOF PET/CT requires not only the use of higher cut-off levels but also visual adaptation by PET readers.

Use of internal references for assessing CT density measurements of the pelvis as replacement for use of an external phantom.

PURPOSE: The purpose of this research is to study the use of an internal reference standard for fat- and muscle as a replacement for an external reference standard with a phantom. By using a phantomless internal reference standard, Hounsfield unit (HU) measurements of various tissues can potentially be assessed in patients with a CT scan of the pelvis without an added phantom at time of CT acquisition. This paves the way for development of a tool for quantification of the change in tissue density in one patient over time and between patients. This could make every CT scan made without contrast available for research purposes. MATERIALS AND METHODS: Fifty patients with unilateral metal-on-metal total hip replacements, scanned together with a calibration reference phantom used in bone mineral density measurements, were included in this study. On computed tomography scans of the pelvis without the use of intravenous iodine contrast, reference values for fat and muscle were measured in the phantom as well as within the patient's body. The conformity between the references was examined with the intra-class correlation coefficient. RESULTS: The mean HU (± SD) of reference values for fat for the internal- and phantom references were -91.5 (±7.0) and -90.9 (±7.8), respectively. For muscle, the mean HU (± SD) for the internal- and phantom references were 59.2 (±6.2) and 60.0 (±7.2), respectively. The intra-class correlation coefficients for fat and muscle were 0.90 and 0.84 respectively and show excellent agreement between the phantom and internal references. CONCLUSION: Internal references can be used with similar accuracy as references from an external phantom. There is no need to use an external phantom to asses CT density measurements of body tissue.

Improving the detection of small lesions using a state-of-the-art time-of-flight PET/CT system and small-voxel reconstructions.

UNLABELLED: A major disadvantage of (18)F-FDG PET involves poor detection of small lesions and lesions with low metabolism, caused by limited spatial resolution and relatively large image voxel size. As spatial resolution and sensitivity are better in new PET systems, it is expected that small-lesion detection could be improved using smaller voxels. The aim of this study was to test this hypothesis using a state-of-the-art time-of-flight PET/CT device. METHODS: (18)F-FDG PET scans of 2 image-quality phantoms (sphere sizes, 4-37 mm) and 39 consecutive patients with lung cancer were analyzed on a time-of-flight PET/CT system. Images were iteratively reconstructed with standard 4 × 4 × 4 mm voxels and smaller 2 × 2 × 2 mm voxels. For the phantom study, we determined contrast-recovery coefficients and signal-to-noise ratios (SNRs). For the patient study, (18)F-FDG PET-positive lesions in the chest and upper abdomen with a volume less than 3.0 mL (diameter, <18 mm) were included. Lesion mean and maximum standardized uptake values (SUVmean and SUVmax, respectively) were determined in both image sets. SNRs were determined by comparing SUVmax and SUVmean with background noise levels. A subanalysis was performed for lesions less than 0.75 mL (diameter, <11 mm). For qualitative analysis of patient data, 3 experienced nuclear medicine physicians gave their preference after visual side-by-side analysis. RESULTS: For phantom spheres 13 mm or less, we found higher contrast-recovery coefficients and SNRs using small-voxel reconstructions. For 66 included (18)F-FDG PET-positive lesions, the average increase in SUVmean and SUVmax using the small-voxel images was 17% and 32%, respectively (P < 0.01). For lesions less than 0.75 mL (21 in total), the average increase was 21% and 44%, respectively. Moreover, averaged over all lesions, the mean and maximum SNR increased by 20% and 27%, respectively (P < 0.01). For lesions less than 0.75 mL, these values increased up to 23% and 46%, respectively. The physicians preferred the small-voxel reconstructions in 76% of cases. CONCLUSION: Supported by a phantom study, there was a visual preference toward (18)F-FDG PET images reconstructed with 2 × 2 × 2 mm voxels and a profound increase in standardized uptake value and SNR for small lesions. Hence, it is expected that small-lesion detection improves using small-voxel reconstructions.