Mattijs Elschot

99mTc-Macroaggregated Albumin Poorly Predicts the Intrahepatic Distribution of 90Y Resin Microspheres in Hepatic Radioembolization

In hepatic 90Y radioembolization, pretreatment 99mTc-macroaggregated albumin (99mTc-MAA) nuclear imaging is used for lung shunt analysis, evaluation of extrahepatic deposition, and sometimes for treatment planning, using a partition model. A high level of agreement between pretreatment 99mTc-MAA distribution and final 90Y-microsphere distribution is assumed. The aim of this study was to investigate the value of pretreatment 99mTc-MAA SPECT to predict intrahepatic posttreatment 90Y-microsphere distribution. Methods: Volumes of interest (VOIs) were delineated on pretreatment contrast-enhanced CT or MR images according to Couinaud liver segmentation. All VOIs were registered to the 99mTc-MAA SPECT and 90Y SPECT images. The 99mTc-MAA SPECT and 90Y SPECT activity counts were normalized to the total administered activity of 90Y. For each VOI, this practice resulted in a predictive amount of 90Y (MBq/cm3) based on 99mTc-MAA SPECT in comparison with an actual amount of 90Y based on 90Y SPECT. Bland–Altman analysis was used to investigate the agreement of the activity distribution between 99mTc-MAA SPECT and 90Y SPECT. Results: A total of 39 procedures (225 VOIs) in 31 patients were included for analysis. The overall mean difference between pretreatment and posttreatment distribution of activity concentration for all segments was −0.022 MBq/cm3 with 95% limits of agreement of −0.581 to 0.537 MBq/cm3 (−28.9 to 26.7 Gy absorbed dose). A difference of >10%, >20%, and >30% of the mean activity per milliliter was found in, respectively, 153 (68%), 97 (43%), and 72 (32%) of the 225 segments. In every 99mTc-MAA procedure, at least 1 segment showed an under- or overestimation of >10%. The position of the catheter tip during administrations, as well as the tumor load of the liver segments, significantly influenced the disagreement. Conclusion: In current clinical practice, 99mTc-MAA distribution does not accurately predict final 90Y activity distribution. Awareness of the importance of catheter positioning and adherence to specific recommendations may lead to optimization of individualized treatment planning based on pretreatment imaging.

T2-weighted MRI-derived textural features reflect prostate cancer aggressiveness: preliminary results

AbstractPurposeTo evaluate the diagnostic relevance of T2-weighted (T2W) MRI-derived textural features relative to quantitative physiological parameters derived from diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) MRI in Gleason score (GS) 3+4 and 4+3 prostate cancers.Materials and Methods3T multiparametric-MRI was performed on 23 prostate cancer patients prior to prostatectomy. Textural features [angular second moment (ASM), contrast, correlation, entropy], apparent diffusion coefficient (ADC), and DCE pharmacokinetic parameters (Ktrans and Ve) were calculated from index tumours delineated on the T2W, DW, and DCE images, respectively. The association between the textural features and prostatectomy GS and the MRI-derived parameters, and the utility of the parameters in differentiating between GS 3+4 and 4+3 prostate cancers were assessed statistically.ResultsASM and entropy correlated significantly (p < 0.05) with both GS and median ADC. Contrast correlated moderately with median ADC. The textural features correlated insignificantly with Ktrans and Ve. GS 4+3 cancers had significantly lower ASM and higher entropy than 3+4 cancers, but insignificant differences in median ADC, Ktrans, and Ve. The combined texture-MRI parameters yielded higher classification accuracy (91%) than the individual parameter sets.ConclusionT2W MRI-derived textural features could serve as potential diagnostic markers, sensitive to the pathological differences in prostate cancers.Key Points• T2W MRI-derived textural features correlate significantly with Gleason score and ADC.n • T2W MRI-derived textural features differentiate Gleason score 3+4 from 4+3 cancers.n • T2W image textural features could augment tumour characterization.

Quantitative Comparison of 124I PET/CT and 131I SPECT/CT Detectability

Radioiodine therapy with 131I is used for treatment of suspected recurrence of differentiated thyroid carcinoma. Pretherapeutic 124I PET/CT with a low activity (∼1% of 131I activity) can be performed to determine whether uptake of 131I, and thereby the desired therapeutic effect, may be expected. However, false-negative 124I PET/CT results as compared with posttherapeutic 131I SPECT/CT have been reported by several groups. The purpose of this study was to investigate whether the reported discrepancies may be ascribed to a difference in lesion detectability between 124I PET/CT and 131I SPECT/CT and, hence, whether the administered 124I activity is sufficient to achieve equal detectability. Methods: Phantom measurements were performed using the National Electrical Manufacturers Association 2007 image-quality phantom. As a measure of detectability, the contrast-to-noise ratio was calculated. The 124I activity was expressed as the percentage of 131I activity required to achieve the same contrast-to-noise ratio. This metric was defined as the detectability equivalence percentage (DEP). Results: Because lower DEPs were obtained for smaller spheres, a relatively low 124I activity was sufficient to achieve similar lesion detectability between 124I PET/CT and 131I SPECT/CT. DEP was 1.5%, 1.9%, 1.9%, 4.4%, 9.0%, and 16.2% for spheres with diameters of 10, 13, 17, 18, 25, and 37 mm, respectively, for attenuation- and scatter-corrected SPECT versus point-spread function (PSF) model–based and time-of-flight (TOF) PET. For no-PSF no-TOF PET, DEP was 3.6%, 2.1%, 3.5%, 7.8%, 15.1%, and 23.3%, respectively. Conclusion: A relatively low 124I activity of 74 MBq (∼1% of 131I activity) is sufficient to achieve similar lesion detectability between 124I PSF TOF PET/CT and 131I SPECT/CT for small spheres (≤10 mm), since the reported DEPs are close to 1%. False-negative 124I PET/CT results as compared with posttherapeutic 131I SPECT/CT may be ascribed to differences in detectability for large lesions (>10 mm) and for no-PSF no-TOF PET, since DEPs are greater than 1%. On the basis of DEPs of 3.5% for lesion diameters of up to 17 mm on no-PSF no-TOF PET, 124I activities as high as 170 MBq may be warranted to obtain equal detectability.

Toward Simultaneous Real-Time Fluoroscopic and Nuclear Imaging in the Intervention Room

PURPOSEnTo investigate the technical feasibility of hybrid simultaneous fluoroscopic and nuclear imaging.nnnMATERIALS AND METHODSnAn x-ray tube, an x-ray detector, and a gamma camera were positioned in one line, enabling imaging of the same field of view. Since a straightforward combination of these elements would block the lines of view, a gamma camera setup was developed to be able to view around the x-ray tube. A prototype was built by using a mobile C-arm and a gamma camera with a four-pinhole collimator. By using the prototype, test images were acquired and sensitivity, resolution, and coregistration error were analyzed.nnnRESULTSnNuclear images (two frames per second) were acquired simultaneously with fluoroscopic images. Depending on the distance from point source to detector, the system resolution was 1.5-1.9-cm full width at half maximum, the sensitivity was (0.6-1.5) × 10(-5) counts per decay, and the coregistration error was -0.13 to 0.15 cm. With good spatial and temporal alignment of both modalities throughout the field of view, fluoroscopic images can be shown in grayscale and corresponding nuclear images in color overlay.nnnCONCLUSIONnMeasurements obtained with the hybrid imaging prototype device that combines simultaneous fluoroscopic and nuclear imaging of the same field of view have demonstrated the feasibility of real-time simultaneous hybrid imaging in the intervention room.

A PET/MRI study towards finding the optimal [18F]Fluciclovine PET protocol for detection and characterisation of primary prostate cancer

Purpose[18F]Fluciclovine PET imaging shows promise for the assessment of prostate cancer. The purpose of this PET/MRI study is to optimise the PET imaging protocol for detection and characterisation of primary prostate cancer, by quantitative evaluation of the dynamic uptake of [18F]Fluciclovine in cancerous and benign tissue.MethodsPatients diagnosed with high-risk primary prostate cancer underwent an integrated [18F]Fluciclovine PET/MRI exam before robot-assisted radical prostatectomy with extended pelvic lymph node dissection. Volumes-of-interest (VOIs) of selected organs (prostate, bladder, blood pool) and sub-glandular prostate structures (tumour, benign prostatic hyperplasia (BPH), inflammation, healthy tissue) were delineated on T2-weighted MR images, using whole-mount histology samples as a reference. Three candidate windows for optimal PET imaging were identified based on the dynamic curves of the mean and maximum standardised uptake value (SUVmean and SUVmax, respectively). The statistical significance of differences in SUV between VOIs were analysed using Wilcoxon rank sum tests (p<0.05, adjusted for multiple testing).ResultsTwenty-eight (28) patients [median (range) age: 66 (55-72) years] were included. An early (W1: 5-10 minutes post-injection) and two late candidate windows (W2: 18-23; W3: 33-38 minutes post-injection) were selected. Late compared with early imaging was better able to distinguish between malignant and benign tissue [W3, SUVmean: tumour vs. BPH 2.5 vs. 2.0 (p<0.001), tumour vs. inflammation 2.5 vs. 1.7 (p<0.001), tumour vs. healthy tissue 2.5 vs. 2.0 (p<0.001); W1, SUVmean: tumour vs. BPH 3.1 vs. 3.1 (p=0.771), tumour vs inflammation 3.1 vs. 2.2 (p=0.021), tumour vs. healthy tissue 3.1 vs. 2.5 (p<0.001)] as well as between high-grade and low/intermediate-grade tumours (W3, SUVmean: 2.6 vs. 2.1 (p=0.040); W1, SUVmean: 3.1 vs. 2.8 (p=0.173)). These differences were relevant to the peripheral zone, but not the central gland.ConclusionLate-window [18F]Fluciclovine PET imaging shows promise for distinguishing between prostate tumours and benign tissue and for assessment of tumour aggressiveness.

A parallel cone collimator for high-energy SPECT

In SPECT using high-energy photon-emitting isotopes, such as 131I, parallel-hole collimators with thick septa are required to limit septal penetration, at the cost of sensitivity and resolution. This study investigated a parallel-hole collimator with cone-shaped holes, which was designed to limit collimator penetration while preserving resolution and sensitivity. The objective was to demonstrate that a single-slice prototype of the parallel-cone (PC) collimator was capable of improving the image quality of high-energy SPECT. Methods: The image quality of the PC collimator was quantitatively compared with that of clinically used low-energy high-resolution (LEHR; for 99mTc) and high-energy general-purpose (HEGP; for 131I and 18F) parallel-hole collimators. First, Monte Carlo simulations of single and double point sources were performed to assess sensitivity and resolution by comparing point-spread functions (PSFs). Second, a prototype PC collimator was used in an experimental phantom study to assess and compare contrast recovery coefficients and image noise. Results: Monte Carlo simulations showed reduced broadening of the PSF due to collimator penetration for the PC collimator as compared with the HEGP collimator (e.g., 0.9 vs. 1.4 cm in full width at half maximum for 131I). Simulated double point sources placed 2 cm apart were separately detectable for the PC collimator, whereas this was not the case for 131I and 18F at distances from the collimator face of 10 cm or more for the HEGP collimator. The sensitivity, measured over the simulated profiles as the total amount of counts per decay, was found to be higher for the LEHR and HEGP collimators than for the PC collimator (e.g., 3.1 × 10−5 vs. 2.9 × 10−5 counts per decay for 131I). However, at equal noise level, phantom measurements showed that contrast recovery coefficients were similar for the PC and LEHR collimators for 99mTc but that the PC collimator significantly improved the contrast recovery coefficients as compared with the HEGP collimator for 131I and 18F. Conclusion: High-energy SPECT imaging with a single-slice prototype of the proposed PC collimator has shown the potential for significantly improved image quality in comparison with standard parallel-hole collimators.

18 F-Fluciclovine PET/MRI for preoperative lymph node staging in high-risk prostate cancer patients

ObjectiveTo investigate the diagnostic potential of simultaneous 18F-fluciclovine PET/MRI for pelvic lymph node (LN) staging in patients with high-risk prostate cancer.MethodsHigh-risk prostate cancer patients (n=28) underwent simultaneous 18F-fluciclovine PET/MRI prior to surgery. LNs were removed according to a predefined template of eight regions. PET and MR images were evaluated for presence of LN metastases according to these regions. Sensitivity/specificity for detection of LN metastases were calculated on patient and region basis. Sizes of LN metastases in regions with positive and negative imaging findings were compared with linear mixed models. Clinical parameters of PET-positive and -negative stage N1 patients were compared with the Mann-Whitney U test.ResultsPatient- and region-based sensitivity/specificity for detection of pelvic LN metastases was 40 %/87.5 % and 35 %/95.7 %, respectively, for MRI and 40 %/100 % and 30 %/100 %, respectively, for PET. LN metastases in true-positive regions were significantly larger than metastases in false-negative regions. PET-positive stage N1 patients had higher metastatic burden than PET-negative N1 patients.ConclusionSimultaneous 18F-fluciclovine PET/MRI provides high specificity but low sensitivity for detection of LN metastases in high-risk prostate cancer patients. 18F-Fluciclovine PET/MRI scan positive for LN metastases indicates higher metastatic burden than negative scan.Key Points• 18F-Fluciclovine PET/MRI has high specificity for detection of lymph node metastasis.• 18F-Fluciclovine PET/MRI lacks sensitivity to replace ePLND.• 18F-Fluciclovine PET/MRI may be used to aid surgery and select adjuvant therapy.• 18F-Fluciclovine PET-positive patients have more extensive disease than PET-negative patients.• Size of metastatic lymph nodes is an important factor for detection.

The Effect of Including Bone in DIXON-based Attenuation Correction for 18F-fluciclovine PET/MRI of Prostate Cancer

The objective of this study was to evaluate the effect of including bone in Dixon-based attenuation correction for 18F-fluciclovine PET/MRI of primary and recurrent prostate cancer. Methods: 18F-fluciclovine PET data from 2 PET/MRI studies—one for staging of high-risk prostate cancer (28 patients) and one for diagnosis of recurrent prostate cancer (81 patients)—were reconstructed with a 4-compartment (reference) and 5-compartment attenuation map. In the latter, continuous linear attenuation coefficients for bone were included by coregistration with an atlas. The SUVmax and mean 50% isocontour SUV (SUViso) of primary, locally recurrent, and metastatic lesions were compared between the 2 reconstruction methods using linear mixed-effects models. In addition, mean SUVs were obtained from bone marrow in the third lumbar vertebra (L3) to investigate the effect of including bone attenuation on lesion–to–bone marrow SUV ratios (SUVRmax and SUVRiso; recurrence study only). The 5-compartment attenuation maps were visually compared with the in-phase Dixon MR images for evaluation of bone registration errors near the lesions. P values of less than 0.05 were considered significant. Results: Sixty-two lesions from 39 patients were evaluated. Bone registration errors were found near 19 (31%) of these lesions. In the remaining 8 primary prostate tumors, 7 locally recurrent lesions, and 28 lymph node metastases without bone registration errors, use of the 5-compartment attenuation map was associated with small but significant increases in SUVmax (2.5%; 95% confidence interval [CI], 2.0%–3.0%; P < 0.001) and SUViso (2.5%; 95% CI, 1.9%–3.0%; P < 0.001), but not SUVRmax (0.2%; 95% CI, −0.5%–0.9%; P = 0.604) and SUVRiso (0.2%; 95% CI −0.6%–1.0%; P = 0.581), in comparison to the 4-compartment attenuation map. Conclusion: The investigated method for atlas-based inclusion of bone in 18F-fluciclovine PET/MRI attenuation correction has only a small effect on the SUVs of soft-tissue prostate cancer lesions, and no effect on their lesion–to–bone marrow SUVRs when using signal from L3 as a reference. The attenuation maps should always be checked for registration artifacts for lesions in or close to the bones.

Geometric distortion correction in prostate diffusion‐weighted MRI and its effect on quantitative apparent diffusion coefficient analysis

To evaluate the effect of correction for B0 inhomogeneity‐induced geometric distortion in echo‐planar diffusion‐weighted imaging on quantitative apparent diffusion coefficient (ADC) analysis in multiparametric prostate MRI.

Multi institutional quantitative phantom study of yttrium-90 PET in PET/MRI: the MR-QUEST study

BackgroundYttrium-90 (90Y) radioembolization involves the intra-arterial delivery of radioactive microspheres to treat hepatic malignancies. Though this therapy involves careful pre-treatment planning and imaging, little is known about the precise location of the microspheres once they are administered. Recently, there has been growing interest post-radioembolization imaging using positron-emission tomography (PET) for quantitative dosimetry and identifying lesions that may benefit from additional salvage therapy. In this study, we aim to measure the inter-center variability of 90Y PET measurements as measured on PET/MRI in preparation for a multi-institutional prospective phase I/II clinical trial.Eight institutions participated in this study and followed a standardized phantom filling and imaging protocol. The NEMA NU2-2012 body phantom was filled with 3xa0GBq of 90Y chloride solution. The phantom was imaged for 30xa0min in listmode on a Siemens Biograph mMR non-TOF PET/MRI scanner at five time points across 10xa0days (0.3–3.0xa0GBq). Raw PET data were sent to a central site for image reconstruction and data analysis. Images were reconstructed with optimal parameters determined from a previous study. Volumes of interest (VOIs) matching the known sphere diameters were drawn on the vendor-provided attenuation map and propagated to the PET images. Recovery coefficients (RCs) and coefficient of variation of the RCs (COV) were calculated from these VOIs for each sphere size and activity level.ResultsMean RCs ranged from 14.5 to 75.4%, with the lowest mean RC coming from the smallest sphere (10xa0mm) on the last day of imaging (0.16xa0MBq/ml) and the highest mean RC coming from the largest sphere (37xa0mm) on the first day of imaging (2.16xa0MBq/ml). The smaller spheres tended to exhibit higher COVs. In contrast, the larger spheres tended to exhibit lower COVs. COVs from the 37xa0mm sphere were <u200925.3% in all scans. For scans with ≥u20090.60xa0MBq/ml, COVs were ≤u200925% in spheres ≥u200922xa0mm. However, for all other spheres sizes and activity levels, COVs were usually >u200925%.ConclusionsPost-radioembolization dosimetry of lesions or other VOIs ≥u200922xa0mm in diameter can be consistently obtained (<u200925% variability) at a multi-institutional level using PET/MRI for any clinically significant activity for 90Y radioembolization.