Free-breathing Arterial Spin Labeling MRI for the Detection of Pulmonary Embolism.

Background Arterial spin labeling (ASL) MRI can be used to assess organ perfusion but has yet to be implemented for perfusion evaluation of the lung. Purpose To evaluate pseudo-continuous ASL (PCASL) MRI for the detection of acute pulmonary embolism (PE) and its potential as an alternative to CT pulmonary angiography (CTPA). Materials and Methods Between November 2020 and November 2021, 97 patients (median age, 61 years; 48 women) with suspected PE were enrolled in this prospective study. PCASL MRI was performed within a 72-hour period following CTPA under free-breathing conditions and included three orthogonal planes. The pulmonary trunk was labeled during systole, and the image was acquired during diastole of the subsequent cardiac cycle. Additionally, multisection, coronal, balanced, steady-state free-precession imaging was carried out. Two radiologists blindly assessed overall image quality, artifacts, and diagnostic confidence (five-point Likert scale, 5 = best). Patients were categorized as positive or negative for PE, and a lobe-wise assessment in PCASL MRI and CTPA was conducted. Sensitivity and specificity were calculated on a patient level with the final clinical diagnosis serving as the reference standard. Interchangeability between MRI and CTPA was also tested with use of an individual equivalence index (IEI). Results PCASL MRI was performed successfully in all patients with high scores for image quality, artifact, and diagnostic confidence (κ ≥ .74). Of the 97 patients, 38 were positive for PE. PCASL MRI depicted PE correctly in 35 of 38 patients with three false-positive and three false-negative findings, resulting in a sensitivity of 35 of 38 patients (92% [95% CI: 79, 98]) and a specificity of 56 of 59 patients (95% [95% CI: 86, 99]). Interchangeability analysis revealed an IEI of 2.6% (95% CI: 1.2, 3.8). Conclusion Free-breathing pseudo-continuous arterial spin labeling MRI depicted abnormal lung perfusion caused by acute pulmonary embolism and may be useful as a contrast material-free alternative to CT pulmonary angiography for selected patients. German Clinical Trials Register no. DRKS00023599 © RSNA, 2023.

Imaging Pulmonary Blood Flow Using Pseudocontinuous Arterial Spin Labeling (PCASL) With Balanced Steady-State Free-Precession (bSSFP) Readout at 1.5T.

BACKGROUND: Quantitative assessment of pulmonary blood flow and visualization of its temporal and spatial distribution without contrast media is of clinical significance. PURPOSE: To assess the potential of electrocardiogram (ECG)-triggered pseudocontinuous arterial spin labeling (PCASL) imaging with balanced steady-state free-precession (bSSFP) readout to measure lung perfusion under free-breathing (FB) conditions and to study temporal and spatial characteristics of pulmonary blood flow. STUDY TYPE: Prospective, observational. SUBJECTS: Fourteen volunteers; three patients with pulmonary embolism. FIELD STRENGTH/SEQUENCES: 1.5T, PCASL-bSSFP. ASSESSMENT: The pulmonary trunk was labeled during systole. The following examinations were performed: 1) FB and timed breath-hold (TBH) examinations with a postlabeling delay (PLD) of 1000 msec, and 2) TBH examinations with multiple PLDs (100-1500 msec). Scan-rescan measurements were performed in four volunteers and one patient. Images were registered and the perfusion was evaluated in large vessels, small vessels, and parenchyma. Mean structural similarity indices (MSSIM) was computed and time-to-peak (TTP) of parenchymal perfusion in multiple PLDs was evaluated. Image quality reading was performed with three independent blinded readers. STATISTICAL TESTS: Wilcoxon test to compare MSSIM, perfusion, and Likert scores. Spearman's correlation to correlate TTP and cardiac cycle duration. The repeatability coefficient (RC) and within-subject coefficient of variation (wCV) for scan-rescan measurements. Intraclass correlation coefficient (ICC) for interreader agreement. RESULTS: Image registration resulted in a significant (P < 0.05) increase of MSSIM. FB perfusion values were 6% higher than TBH (3.28 ± 1.09 vs. 3.10 ± 0.99 mL/min/mL). TTP was highly correlated with individuals' cardiac cycle duration (Spearman = 0.89, P < 0.001). RC and wCV were better for TBH than FB (0.13-0.19 vs. 0.47-1.54 mL/min/mL; 6-7 vs. 19-60%). Image quality was rated very good, with ICCs 0.71-0.89. DATA CONCLUSION: ECG-triggered PCASL-bSSFP imaging of the lung at 1.5T can provide very good image quality and quantitative perfusion maps even under FB. The course of labeled blood through the lung shows a strong dependence on the individuals' cardiac cycle duration. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 2 J. MAGN. RESON. IMAGING 2020;52:1767-1782.

18F-FDG-PET detects complete response to PD1-therapy in melanoma patients two weeks after therapy start.

PURPOSE: The aim of the study was to evaluate if 18F-FDG-PET has the potential to detect complete responders to PD1-therapy in patients with unresectable metastasized melanoma two weeks after therapy initiation. METHODS: Between September 2014 and May 2016, ten patients (four females; 65 ± 12 y) received a whole-body 18F-FDG-PET/MRI examination at three time points: Before therapy start (t0, base-line), two weeks (t1, study examination) and three months after treatment initiation (t2, reference standard). Therapy response was assessed with PET response criteria in solid tumors (PERCIST). Time to progression and overall survival (OS) were obtained for all patients. RESULTS: Three patients with partial metabolic response in PET at t1 turned out to have complete response at t2. No tumor relapse was observed in those patients so far (observation period: 265, 511 and 728 days, respectively). At t2, progressive metabolic disease (PMD) was seen in six patients from whom four showed PMD and two showed stable metabolic disease (SMD) at t1. OS in patients with PMD at t2 varied between 148 and 814 days. SMD at both t1 and t2 was seen in one patient, tumor progress was observed after 308 days. CONCLUSION: Our study indicates that whole-body 18F-FDG-PET might be able to reliably identify complete responders to PD1-therapy as early as two weeks after therapy initiation in stage IV melanoma patients. This might help to shorten therapy regimes and avoid unnecessary side effects in the future.

Simultaneous multislice diffusion-weighted imaging in whole-body positron emission tomography/magnetic resonance imaging for multiparametric examination in oncological patients.

OBJECTIVES: The aim of this study was to compare the diagnostic performance of simultaneous multislice diffusion-weighted imaging (DWI-SMS) with that of standard DWI (DWI-STD) in whole-body 3-T PET/MRI examination protocols in oncological patients. METHODS: In a phantom study, we evaluated the apparent diffusion coefficients (ADC) from the two techniques. In ten volunteers, we assessed ADC values in different organs. In 20 oncological patients, we evaluated subjective image quality (Likert scale, 5 indicating excellent) and artefacts in different body regions. We also rated the conspicuity and acquired the ADC values of PET-positive tumorous lesions. RESULTS: The scan time for the whole-body DWI-SMS examinations was 40% shorter than the scan time for the DWI-STD examinations (84 s vs. 140 s per table position). The phantom and volunteer studies showed lower ADC values from DWI-SMS in the liver and muscle (psoas muscle 1.4 vs. 1.3). In patients, DWI-SMS provided poorer subjective image quality in the thoracoabdominal region (3.0 vs. 3.8, p = 0.02) and overall more artefacts (138 vs. 105). No significant differences regarding conspicuity and ADC values of lesions were found. CONCLUSIONS: DWI-SMS seems to provide reliable conspicuity and ADC values of tumorous lesions similar to those provided by DWI-STD. Therefore, although providing poorer image quality in certain regions, DWI-SMS can clearly reduce PET/MRI scan times in oncological patients. KEY POINTS: • DWI-SMS can reduce PET/MRI scan times in oncological patients. • DWI-SMS provides reliable ADC values and good lesion conspicuity similar to those provided by DWI-STD. • DWI-SMS may provide poorer image quality in regions with low signal.

Fast non-enhanced abdominal examination protocols in PET/MRI for patients with neuroendocrine tumors (NET): comparison to multiphase contrast-enhanced PET/CT.

PURPOSE: To evaluate fast non-enhanced protocols for abdominal PET/MRI in comparison to contrast-enhanced PET/CT with somatostatin receptor (SSR)-specific radiotracers regarding effectiveness of lesion detection in NET patients. METHODS: This was a retrospective analysis of 29 patients (12 male, 57 ± 13 years) who underwent PET/CT and subsequently PET/MRI at the same day. Two readers evaluated independently four PET/MRI setups: (I) PET + T2 Half Fourier Acquisition Single Shot Turbo Spin Echo (T2 HASTE), (II) PET + T2 HASTE + T2-weighted spin-echo sequence (T2 TSE), III) PET + T2 HASTE + Diffusion Weighted Imaging (DWI) and (IV) PET + T2 HASTE + T2 TSE + DWI. A consensus reading of PET/MRI and PET/CT including follow-up examinations served as the reference standard for lesion-based analysis. Lesion sizes were assessed. RESULTS: Setup IV provided comparable overall detection rates as PET/CT in both readers: PET/MRI 91.5%/92.9% versus 89.7% in PET/CT. In liver and bone lesions (mean diameter: 1.9 and 1.5 cm), PET/MRI was equal or superior to PET/CT: 98%/98% versus 85% in PET/CT; 100%/95% versus 100% in PET/CT, but inferior in pancreatic lesions, small bowel lesions and lymph node metastases (mean diameter: 1.3, 0.5 and 1.8 cm). CONCLUSION: A non-enhanced MR protocol comprising T2 HASTE, T2 TSE and DWI for SSR-PET/MRI seems to provide comparable effectiveness in lesions detection as multiphase contrast-enhanced PET/CT. It might, therefore, serve as valid alternative, e.g., for follow-up examinations in patients with unresectable NET and kidney failure.

Self-navigated 4D cartesian imaging of periodic motion in the body trunk using partial k-space compressed sensing.

PURPOSE: To enable fast and flexible high-resolution four-dimensional (4D) MRI of periodic thoracic/abdominal motion for motion visualization or motion-corrected imaging. METHODS: We proposed a Cartesian three-dimensional k-space sampling scheme that acquires a random combination of k-space lines in the ky/kz plane. A partial Fourier-like constraint compacts the sampling space to one half of k-space. The central k-space line is periodically acquired to allow an extraction of a self-navigated respiration signal used to populate a k-space of multiple breathing positions. The randomness of the acquisition (induced by periodic breathing pattern) yields a subsampled k-space that is reconstructed using compressed sensing. Local image evaluations (coefficient of variation and slope steepness through organs) reveal information about motion resolvability. Image quality is inspected by a blinded reading. Sequence and reconstruction method are made publicly available. RESULTS: The method is able to capture and reconstruct 4D images with high image quality and motion resolution within a short scan time of less than 2 min. These findings are supported by restricted-isometry-property analysis, local image evaluation, and blinded reading. CONCLUSION: The proposed method provides a clinical feasible setup to capture periodic respiratory motion with a fast acquisition protocol and can be extended by further surrogate signals to capture additional periodic motions. Retrospective parametrization allows for flexible tuning toward the targeted applications. Magn Reson Med 78:632-644, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Towards tracer dose reduction in PET studies: Simulation of dose reduction by retrospective randomized undersampling of list-mode data.

OBJECTIVE: Optimization of tracer dose regimes in positron emission tomography (PET) imaging is a trade-off between diagnostic image quality and radiation exposure. The challenge lies in defining minimal tracer doses that still result in sufficient diagnostic image quality. In order to find such minimal doses, it would be useful to simulate tracer dose reduction as this would enable to study the effects of tracer dose reduction on image quality in single patients without repeated injections of different amounts of tracer. The aim of our study was to introduce and validate a method for simulation of low-dose PET images enabling direct comparison of different tracer doses in single patients and under constant influencing factors. METHODS: (18)F-fluoride PET data were acquired on a combined PET/magnetic resonance imaging (MRI) scanner. PET data were stored together with the temporal information of the occurrence of single events (list-mode format). A predefined proportion of PET events were then randomly deleted resulting in undersampled PET data. These data sets were subsequently reconstructed resulting in simulated low-dose PET images (retrospective undersampling of list-mode data). This approach was validated in phantom experiments by visual inspection and by comparison of PET quality metrics contrast recovery coefficient (CRC), background-variability (BV) and signal-to-noise ratio (SNR) of measured and simulated PET images for different activity concentrations. In addition, reduced-dose PET images of a clinical (18)F-FDG PET dataset were simulated using the proposed approach. RESULTS: (18)F-PET image quality degraded with decreasing activity concentrations with comparable visual image characteristics in measured and in corresponding simulated PET images. This result was confirmed by quantification of image quality metrics. CRC, SNR and BV showed concordant behavior with decreasing activity concentrations for measured and for corresponding simulated PET images. Simulation of dose-reduced datasets based on clinical (18)F-FDG PET data demonstrated the clinical applicability of the proposed data. CONCLUSION: Simulation of PET tracer dose reduction is possible with retrospective undersampling of list-mode data. Resulting simulated low-dose images have equivalent characteristics with PET images actually measured at lower doses and can be used to derive optimal tracer dose regimes.

Additional Value of FDG-PET/MRI Complementary to Sentinel Lymphonodectomy for Minimal Invasive Lymph Node Staging in Patients with Endometrial Cancer: A Prospective Study.

BACKGROUND: Lymph node metastases (LNM) are rare in early-stage endometrial cancer, but a diagnostic systematic lymphadenectomy (LNE) is often performed to achieve reliable N-staging. Therefore, this prospective study aimed to evaluate the benefit of [18F]-Fluorodeoxyglucose (FDG) PET/MRI complementary to SPECT/CT guided sentinel lymphonodectomy (SLNE) for a less invasive N-staging Methods: 79 patients underwent a whole-body FDG-PET/MRI, SLN mapping with 99mTc-Nanocolloid SPECT/CT and indocyanine green (ICG) fluoroscopy followed by LNE which served as ground truth. RESULTS: FDG-PET/MRI was highly specific in N-staging (97.2%) but revealed limited sensitivity (66.7%) due to missed micrometastases. In contrast, bilateral SLN mapping failed more often in patients with macrometastases. The combination of SLN mapping and FDG-PET/MRI increased the sensitivity from 66.7% to 77.8%. Additional SLN labeling with dye (ICG) revealed a complete SLN mapping in 80% (8/10) of patients with failed or incomplete SLN detection in SPECT/CT, reducing the need for diagnostic systematic LNE up to 87%. FDG-PET/MRI detected para-aortic LNM in three out of four cases and a liver metastasis. CONCLUSIONS: The combination of FDG-PET/MRI and SLNE can reduce the need for diagnostic systematic LNE by up to 87%. PET/MRI complements the SLN technique particularly in the detection of para-aortic LNM and occasional distant metastases.

A novel approach to guide GD2-targeted therapy in pediatric tumors by PET and [64Cu]Cu-NOTA-ch14.18/CHO.

Background: The tumor-associated disialoganglioside GD2 is a bona fide immunotherapy target in neuroblastoma and other childhood tumors, including Ewing sarcoma and osteosarcoma. GD2-targeting antibodies proved to be effective in neuroblastoma and GD2-targeting chimeric antigen receptors (CAR)- expressing T cells as well as natural killer T cells (NKTs) are emerging. However, assessment of intra- and intertumoral heterogeneity has been complicated by ineffective immunohistochemistry as well as sampling bias in disseminated disease. Therefore, a non-invasive approach for the assessment and visualization of GD2 expression in-vivo is of upmost interest and might enable a more appropriate treatment stratification. Methods: Recently, [64Cu]Cu-NOTA-ch14.18/CHO (64Cu-GD2), a radiolabeled GD2-antibody for imaging with Positron-Emission-Tomography (PET) was developed. We here report our first clinical patients' series (n = 11) in different pediatric tumors assessed with 64Cu-GD2 PET/MRI. GD2-expression in tumors and tissue uptake in organs was evaluated by semiquantitative measurements of standardized uptake values (SUV) with PET/MRI on day 1 p.i. (n = 11) as well as on day 2 p.i. (n = 6). Results: In 8 of 9 patients with suspicious tumor lesions on PET/MRI at least one metastasis showed an increased 64Cu-GD2 uptake and a high tracer uptake (SUVmax > 10) was measured in 4 of those 8 patients. Of note, sufficient image quality with high tumor to background contrast was readily achieved on day 1. In case of 64Cu-GD2-positive lesions, an excellent tumor to background ratio (at least 6:1) was observed in bones, muscles or lungs, while lower tumor to background contrast was seen in the spleen, liver and kidneys. Furthermore, we demonstrated extensive tumor heterogeneity between patients as well as among different metastatic sites in individual patients. Dosimetry assessment revealed a whole-body dose of only 0.03 mGy/MBq (range 0.02-0.04). Conclusion: 64Cu-GD2 PET/MRI enables the non-invasive assessment of individual heterogeneity of GD2 expression, which challenges our current clinical practice of patient selection, stratification and immunotherapy application scheme for treatment with anti-GD2 directed therapies.

Multiparametric Oncologic Hybrid Imaging: Machine Learning Challenges and Opportunities.

BACKGROUND: Machine learning (ML) is considered an important technology for future data analysis in health care. METHODS: The inherently technology-driven fields of diagnostic radiology and nuclear medicine will both benefit from ML in terms of image acquisition and reconstruction. Within the next few years, this will lead to accelerated image acquisition, improved image quality, a reduction of motion artifacts and - for PET imaging - reduced radiation exposure and new approaches for attenuation correction. Furthermore, ML has the potential to support decision making by a combined analysis of data derived from different modalities, especially in oncology. In this context, we see great potential for ML in multiparametric hybrid imaging and the development of imaging biomarkers. RESULTS AND CONCLUSION: In this review, we will describe the basics of ML, present approaches in hybrid imaging of MRI, CT, and PET, and discuss the specific challenges associated with it and the steps ahead to make ML a diagnostic and clinical tool in the future. KEY POINTS: · ML provides a viable clinical solution for the reconstruction, processing, and analysis of hybrid imaging obtained from MRI, CT, and PET..

[Multiparametric MRI of the prostate: requirements and principles regarding diagnostic reporting]. / Die multiparametrische MRT der Prostata: Anforderungen und Grundlagen der Befundung.

Multiparametric MRI (mpMRI) is one of the primary diagnostic tools for detecting clinically relevant prostate cancer. It should be routinely used in addition to urological investigations owing to its higher diagnostic yield than systematic biopsies. However, combining targeted and systematic biopsies achieves the highest diagnostic rate. The Prostate Imaging Reporting and Data System (PI-RADS Version 2.1) standardizes the acquisition and interpretation of mpMRI of the prostate. It consists of high-resolution T2- and diffusion-weighted images, the corresponding apparent diffusion coefficient (ADC) maps, and a dynamic contrast-enhanced sequence. Reports describe the increasing likelihood of clinically significant prostate cancer with PI-RADS categories 1-5. The MRI sequence determining the PI-RADS category of a lesion depends on its location within the prostate: in the transitional zone, the T2-weighted sequence and, in the peripheral zone, the diffusion-weighted sequence are the primary determinants. The diffusion-weighted and contrast-enhanced sequences provide secondary classification for the transitional and peripheral zones, respectively. This review summarizes and illustrates the diagnostic criteria defined in PI-RADS 2.1. In addition, evidence for mpMRI of the prostate, its indication and implementation are described.

Functional MRI to quantify perfusion changes of a renal allograft after embolization of an arteriovenous fistula.

Acute allograft injury was observed in a 37-year-old woman within a few weeks after kidney transplantation. Neither renal ultrasound nor computerized tomography (CT) and magnetic resonance (MR) angiography revealed any anomaly. An MR protocol was then performed including arterial spin labeling and intravoxel incoherent motion diffusion weighted imaging. Both arterial spin labeling and the perfusion fraction in the diffusion weighted imaging showed decreased perfusion compared to reference values. The patient subsequently underwent angiography, where an arteriovenous fistula in the upper calix of the transplant kidney was detected and immediate embolization was performed. A second functional MR, performed one week later, demonstrated a 40% increase in organ perfusion. We conclude that functional MR with arterial spin labeling and intravoxel incoherent motion have the potential to provide complementary information of clinical value to conventional imaging for monitoring renal allografts.

Impact of Tracer Dose Reduction in [18 F]-Labelled Fluorodeoxyglucose-Positron Emission Tomography ([18 F]-FDG)-PET) on Texture Features and Histogram Indices: A Study in Homogeneous Tissues of Phantom and Patient.

BACKGROUND: Histogram indices (HIs) and texture features (TFs) are considered to play an important role in future oncologic PET-imaging and it is unknown how these indices are affected by changes of tracer doses. A randomized undersampling of PET list mode data enables a simulation of tracer dose reduction. We performed a phantom study to compare HIs/TFs of simulated and measured tracer dose reductions and evaluated changes of HIs/TFs in the liver of patients with PETs from simulated reduced tracer doses. Overall, 42 HIs/TFs were evaluated in a NEMA phantom at measured and simulated doses (stepwise reduction of [18 F] from 100% to 25% of the measured dose). [18 F]-FDG-PET datasets of 15 patients were simulated from 3.0 down to 0.5 MBq/kgBW in intervals of 0.25 MBq/kgBW. HIs/TFs were calculated from two VOIs placed in physiological tissue of the right and left liver lobe and linear correlations and coefficients of variation analysis were performed. RESULTS: All 42 TFs did not differ significantly in measured and simulated doses (p > 0.05). Also, 40 TFs showed the same behaviour over dose reduction regarding differences in the same group (measured or simulated), and for 26 TFs a linear behaviour over dose reduction for measured and simulated doses could be validated. Out of these, 13 TFs could be identified, which showed a linear change in TF value in both the NEMA phantom and patient data and therefore should maintain the same informative value when transferred in a dose reduction setting. Out of this Homogeneity 2, Entropy and Zone size non-uniformity are of special interest because they have been described as preferentially considerable for tumour heterogeneity characterization. CONCLUSIONS: We could show that there was no significant difference of measured and simulated HIs/TFs in the phantom study and most TFs reveal a linear behaviour over dose reduction, when tested in homogeneous tissue. This indicates that texture analysis in PET might be robust to dose modulations.

Selective Internal Radiotherapy (SIRT) and Chemosaturation Percutaneous Hepatic Perfusion (CS-PHP) for Metastasized Uveal Melanoma: A Retrospective Comparative Study.

Even with liver-targeted therapies, uveal melanoma with hepatic metastasis remains a challenge. The aim of this study was to compare the outcome of patients treated with either SIRT or CS-PHP. We included 62 patients with hepatic metastasized uveal melanoma (n = 34 with SIRT, receiving 41 cycles; n = 28 with CS-PHP, receiving 56 cycles) that received their treatments between 12/2013 and 02/2020 at a single center. We evaluated their response according to the RECIST 1.1, as well as progression-free survival (PFS) and overall survival (OS), after the initiation of the first cycle of the liver-directed treatment using Cox regression, adjusted via propensity score analysis for confounders, including the amount of hepatic involvement. The disease control rate was 18% for SIRT and 30% for CS-PHP. The median (range) of PFS was 127.5 (19-1912) days for SIRT and 408.5 (3-1809) days for CS-PHP; adjusted Cox regression showed no significant difference (p = 0.090). The median (range) of OS was 300.5 (19-1912) days for SIRT and 516 (5-1836) days for CS-PHP; adjusted Cox regression showed a significant difference (p = 0.006). In our patient cohort, patients treated with CS-PHP showed a significantly longer OS than patients treated with SIRT. CS-PHP might therefore be preferable for patients with liver-dominant metastatic uveal melanoma.

How [18F]-FDG-PET/CT Affects Clinical Management of Patients with Germ Cell Tumors in the Real World.

OBJECTIVE: The aim of this study was to evaluate the impact of PET/CT on clinical management of patients with germ cell tumors (GCTs) conducted in a real-world setting, including avoidance of invasive procedures, additional diagnostic imaging, and changes in treatment. METHODS: Patients with GCTs were prospectively enrolled into a PET/CT registry study between May 2013 and April 2021. Intended patient management prior and after PET/CT was documented using standardized questionnaires. Changes in oncologic staging and clinical management after PET/CT were recorded, including planned treatment and planned additional diagnostics. RESULTS: Forty-three male patients with GCTs were included consecutively in this study. After PET/CT, oncologic staging changed in 22/43 patients (51%), with upstaging in seven cases (16%), downstaging in ten cases (23%), and cancer relapse in five cases (11%). The number of patients with intended curative treatment remained stable, while a considerable change in intended therapeutic intervention was noted after PET/CT, with an increase in planned chemotherapy from three to eleven patients and a decrease in planned surgical resection from eleven to two patients. In addition, PET/CT contributed to preventing patients from intended invasive procedures including biopsy and surgery in 8/43 (19%) cases and from additional diagnostic procedures in 25 (58%) cases. CONCLUSION: With the use of FDG-PET/CT as a tool to guide patient management in GCTs, we observed a notable impact on clinical staging and a consequent reduction in the need for additional invasive and diagnostic procedures. These findings are expected to be even more consequential in the future as treatment modalities improve and the life expectancy of GCT patients further increases. KEY POINTS: PET/CT considerably influences the clinical stage of GCT patients. PET/CT has remarkable influence on the choice of therapeutic interventions and reduces additional diagnostic procedures.

Whole-Body Magnetic Resonance Imaging (MRI) for Staging Melanoma Patients in Direct Comparison to Computed Tomography (CT): Results from a Prospective Positron Emission Tomography (PET)/CT and PET/MRI Study.

PURPOSE: The consideration of radiation exposure is becoming more important in metastatic melanoma due to improved prognoses. The aim of this prospective study was to investigate the diagnostic performance of whole-body (WB) magnetic resonance imaging (MRI) in comparison to computed tomography (CT) with 18F-FDG positron emission tomography (PET)/CT and 18F-PET/MRI together with a follow-up as the reference standard. METHODS: Between April 2014 and April 2018, a total of 57 patients (25 females, mean age of 64 ± 12 years) underwent WB-PET/CT and WB-PET/MRI on the same day. The CT and MRI scans were independently evaluated by two radiologists who were blinded to the patients' information. The reference standard was evaluated by two nuclear medicine specialists. The findings were categorized into different regions: lymph nodes/soft tissue (I), lungs (II), abdomen/pelvis (III), and bone (IV). A comparative analysis was conducted for all the documented findings. Inter-reader reliability was assessed using Bland-Altman procedures, and McNemar's test was utilized to determine the differences between the readers and the methods. RESULTS: Out of the 57 patients, 50 were diagnosed with metastases in two or more regions, with the majority being found in region I. The accuracies of CT and MRI did not show significant differences, except in region II where CT detected more metastases compared to MRI (0.90 vs. 0.68, p = 0.008). On the other hand, MRI had a higher detection rate in region IV compared to CT (0.89 vs. 0.61, p > 0.05). The level of agreement between the readers varied depending on the number of metastases and the specific region, with the highest agreement observed in region III and the lowest observed in region I. CONCLUSIONS: In patients with advanced melanoma, WB-MRI has the potential to serve as an alternative to CT with comparable diagnostic accuracy and confidence across most regions. The observed limited sensitivity for the detection of pulmonary lesions might be improved through dedicated lung imaging sequences.

Non-invasive estimation of split renal function from routine 68Ga-SSR-PET/CT scans.

Objective: Patients with impaired kidney function are at elevated risk for nephrotoxicity and hematotoxicity from peptide receptor radionuclide therapy (PPRT) for advanced neuroendocrine tumors. Somatostatin receptor (SSR)-PET/CT imaging is the method of choice to identify sufficient SSR expression as a prerequisite for PRRT. Therefore, our study aimed to explore whether split renal function could be evaluated using imaging data from routine SSR-PET/CT prior to PRRT. Methods: In total, 25 consecutive patients who underwent SSR-PET/CT (Siemens Biograph mCT®) before PRRT between June 2019 and December 2020 were enrolled in this retrospective study. PET acquisition in the caudocranial direction started at 20 ± 0.5 min after an i.v. injection of 173 ± 20 MBq [68Ga]Ga-ha DOTATATE, and the kidneys were scanned at 32 ± 0.5 min p.i. The renal parenchyma was segmented semi-automatically using an SUV-based isocontour (SUV between 5 and 15). Multiple parameters including SUVmean of renal parenchyma and blood pool, as well as parenchyma volume, were extracted, and accumulation index (ACI: renal parenchyma volume/SUVmean) and total kidney accumulation (TKA: SUVmean x renal parenchyma volume) were calculated. All data were correlated with the reference standard tubular extraction rate (TER-MAG) from [99mTc]Tc-MAG3 scintigraphy and glomerular filtration rate (GFRCDK - EPI). Results: SUVmean of the parenchymal tracer retention showed a negative correlation with TERMAG (r: -0.519, p < 0.001) and GFRCDK - EPI (r: -0.555, p < 0.001) at 32 min p.i. The herein-introduced ACI revealed a significant correlation (p < 0.05) with the total tubular function (r: 0.482), glomerular renal function (r: 0.461), split renal function (r: 0.916), and absolute single-sided renal function (r: 0.549). The mean difference between the split renal function determined by renal scintigraphy and ACI was 1.8 ± 4.2 % points. Conclusion: This pilot study indicates that static [68Ga]Ga-ha DOTATATE PET-scans at 32 min p.i. may be used to estimate both split renal function and absolute renal function using the herein proposed "Accumulation Index" (ACI).

Diagnostic Performance of Dynamic Whole-Body Patlak [18F]FDG-PET/CT in Patients with Indeterminate Lung Lesions and Lymph Nodes.

BACKGROUND: Static [18F]FDG-PET/CT is the imaging method of choice for the evaluation of indeterminate lung lesions and NSCLC staging; however, histological confirmation of PET-positive lesions is needed in most cases due to its limited specificity. Therefore, we aimed to evaluate the diagnostic performance of additional dynamic whole-body PET. METHODS: A total of 34 consecutive patients with indeterminate pulmonary lesions were enrolled in this prospective trial. All patients underwent static (60 min p.i.) and dynamic (0-60 min p.i.) whole-body [18F]FDG-PET/CT (300 MBq) using the multi-bed-multi-timepoint technique (Siemens mCT FlowMotion). Histology and follow-up served as ground truth. Kinetic modeling factors were calculated using a two-compartment linear Patlak model (FDG influx rate constant = Ki, metabolic rate = MR-FDG, distribution volume = DV-FDG) and compared to SUV using ROC analysis. RESULTS: MR-FDGmean provided the best discriminatory power between benign and malignant lung lesions with an AUC of 0.887. The AUC of DV-FDGmean (0.818) and SUVmean (0.827) was non-significantly lower. For LNM, the AUCs for MR-FDGmean (0.987) and SUVmean (0.993) were comparable. Moreover, the DV-FDGmean in liver metastases was three times higher than in bone or lung metastases. CONCLUSIONS: Metabolic rate quantification was shown to be a reliable method to detect malignant lung tumors, LNM, and distant metastases at least as accurately as the established SUV or dual-time-point PET scans.