Hybrid Positron Emission Tomography Research Articles

Design and characterization of a hybrid PET detector with DOI capability.

Monolithic or semi-monolithic detectors are attractive for positron emission tomography (PET) scanners with depth-of-interaction (DOI) capability. However, they often require complicated calibrations to determine the interaction positions of gamma photons. We introduce a novel hybrid detector design that combines pixelated and semi-monolithic elements to achieve DOI capability while simplifying the calibrations for positioning. A prototype detector with eight hybrid lutetium-yttrium oxyorthosilicate (LYSO)layers having dimensions of 25.8×12.9×15mm3 was constructed. The energy-weighted and energy-squared weighted averages were used for estimating the x- (pixelated direction) and y-positions (non-pixelated direction). Pseudo-pixels were defined as discrete areas on the flood image based on the crystal look-up table (LUT). The intrinsic spatial resolutions in the pixelated and non-pixelated directions were measured. The ratio of the maximum to the sum of the multipixel photon counter (MPPC) signals was used to estimate the DOI positions. The coincidence timing resolution (CTR) was measured using the average and energy-weighted average of the earliest n time stamps. Two energy windows of 250-700 and 400-600keV were applied for the measurements. The pattern of the flood images showed discrete event clusters, demonstrating that simple calibrations for determining the x- and y-positions of events could be achieved. Under 400-600keV energy window, the average intrinsic spatial resolutions were 1.15 and 1.34mm for the pixelated and non-pixelated directions; the average DOI resolution of the second row of pseudo-pixels was 5.1mm in full width at half maximum (FWHM); when using the energy-weighted average of the earliest four-time stamps, the best CTR of 350ps was achieved. Applying a broader energy window of 250-700keV only slightly degrades the DOI resolution while maintaining the intrinsic resolution; the best CTR degrades to 410ps. The proposed hybrid detector concept was verified, and a prototype detector showed high performance for 3D positioning and timing resolution. The novel detector concept shows promise for preclinical and clinical PET scanners with DOI capability.

Low-dose and standard-dose whole-body [18F]FDG-PET/CT imaging: implications for healthy controls and lung cancer patients

Aim: High-sensitivity hybrid positron emission tomography (PET) imaging using advanced whole-body (WB) or total-body PET/computed tomography (CT) systems permits reducing injected tracer activity while preserving diagnostic quality. Such approaches are promising for healthy control studies or exploring inter-organ communication in systemic diseases. This study assessed test/retest variations in the fluoro-2-deoxy-D-glucose (FDG) uptake in key organs from low-dose (LD) and standard-dose (STD) [18F]FDG-PET/CT imaging protocols in healthy controls and lung cancer patients.Methods: A total of 19 healthy controls (19–62 years, 46–104 kg, 10 M/9 F) and 7 lung cancer patients (47–77 years, 50–88 kg, 4 M/3 F) underwent [18F]FDG-PET/CT imaging. All subjects were first injected (“test,” LD) with 28 ± 2 MBq FDG and underwent a dynamic (0–67 min post-injection) WB imaging protocol with LD-CT. Then, 90 min post-LD injection, the subjects were repositioned and injected with 275 ± 16 MBq FDG (“retest,” STD). Second LD-CT and STD-CT scans were acquired for healthy controls and patients, respectively. Static images (55–67 min post-injection) were considered for subsequent analysis. The CT images were used to automatically segment the target volumes of interest. Standardized uptake values normalized to the body weight (SUVBW) were extracted for each volume of interest. The mean SUVBW were compared for both LD/STD conditions with paired t-tests. In patients, FDG-avid lesions were manually delineated on LD and STD static images. Effective dose levels were estimated from both the CT and PET acquisitions.Results: Organ-based mean SUVBW were similar between the LD and STD (mean %difference ≤5%) in both healthy controls and cancer patients, except in the heart. Intra-control test/retest variability was significant in the brain, heart, and skeletal muscle (p < 0.05). While 17 lesions were delineated on the STD images of the patients, only 10/17 lesions were identified on the LD images due to increased image noise. Lesion-based mean SUVBW were similar between LD and STD acquisitions (p = 0.49, %difference = 10%). In patients, the effective doses were (1.9 ± 0.2) mSv (LD-CT), (16.6 ± 5.4) mSv (STD-CT), (0.5 ± 0.1) mSv (LD-PET), and (4.6 ± 0.3) mSv (STD-PET).Conclusion: LD and STD [18F]FDG injections in healthy controls and lung cancer patients yielded comparable mean SUVBW, except in the heart. Dose levels may be reduced for [18F]FDG-PET imaging without a loss in mean SUVBW accuracy, promoting LD-PET/CT protocols for studying multi-organ metabolic patterns. In oncology patients, this approach may be hindered by a lower diagnostic quality in the presence of significant noise.

Automated multiclass segmentation, quantification, and visualization of the diseased aorta on hybrid PET/CT-SEQUOIA.

Cardiovascular disease is the most common cause of death worldwide, including infection and inflammation related conditions. Multiple studies have demonstrated potential advantages of hybrid positron emission tomography combined with computed tomography (PET/CT) as an adjunct to current clinical inflammatory and infectious biochemical markers. To quantitatively analyze vascular diseases at PET/CT, robust segmentation of the aorta is necessary. However, manual segmentation is extremely time-consuming and labor-intensive. To investigate the feasibility and accuracy of an automated tool to segment and quantify multiple parts of the diseased aorta on unenhanced low-dose computed tomography (LDCT) as an anatomical reference for PET-assessed vascular disease. A software pipeline was developed including automated segmentation using a 3D U-Net, calcium scoring, PET uptake quantification, background measurement, radiomics feature extraction, and 2D surface visualization of vessel wall calcium and tracer uptake distribution. To train the 3D U-Net, 352 non-contrast LDCTs from (2-[18F]FDG and Na[18F]F) PET/CTs performed in patients with various vascular pathologies with manual segmentation of the ascending aorta, aortic arch, descending aorta, and abdominal aorta were used. The last 22 consecutive scans were used as a hold-out internal test set. The remaining dataset was randomly split into training (n=264; 80%) and validation (n=66; 20%) sets. Further evaluation was performed on an external test set of 49 PET/CTs. The dice similarity coefficient (DSC) and Hausdorff distance (HD) were used to assess segmentation performance. Automatically obtained calcium scores and uptake values were compared with manual scoring obtained using clinical softwares (syngo.via and Affinity Viewer) in six patient images. intraclass correlation coefficients (ICC) were calculated to validate calcium and uptake values. Fully automated segmentation of the aorta using a 3D U-Net was feasible in LDCT obtained from PET/CT scans. The external test set yielded a DSC of 0.867±0.030 and HD of 1.0 [0.6-1.4] mm, similar to an open-source model with a DSC of 0.864±0.023 and HD of 1.4 [1.0-1.8] mm. Quantification of calcium and uptake values were in excellent agreement with clinical software (ICC: 1.00 [1.00-1.00] and 0.99 [0.93-1.00] for calcium and uptake values, respectively). We present an automated pipeline to segment the ascending aorta, aortic arch, descending aorta, and abdominal aorta on LDCT from PET/CT and to accurately provide uptake values, calcium scores, background measurement, radiomics features, and a 2D visualization. We call this algorithm SEQUOIA (SEgmentation, QUantification, and visualizatiOn of the dIseased Aorta) and is available at https://github.com/UMCG-CVI/SEQUOIA. This model could augment the utility of aortic evaluation at PET/CT studies tremendously, irrespective of the tracer, and potentially provide fast and reliable quantification of cardiovascular diseases in clinical practice, both for primary diagnosis and disease monitoring.

Myocardial fibrosis activity following ST-segment elevation myocardial infarction

Abstract Background Myocardial fibrosis following myocardial infarction (MI) is a key healing mechanism and involves widespread fibroblast activation. Once activated, fibroblasts express fibroblast activation protein (FAP) (1). Hybrid positron emission tomography (PET) imaging of radiolabelled fibroblast activation protein inhibitor (FAPI) fused with cardiovascular magnetic resonance (68Ga-FAPI PET/MR) is an emerging method for assessing myocardial fibrosis activity that may provide additional insights into the recovery of the heart following MI. Methods Forty patients with acute (<4 weeks), 19 with recent (12 weeks), and 19 with prior established ST-segment elevation MI (>12 months), and 20 healthy volunteer participants underwent 68Ga-FAPI PET/MR. Participants were imaged 30 min after administration of 100-200 MBq 68Ga-FAPI-04. Image analysis was performed using FusionQuant (Cedars Sinai, Los Angeles, California). 68Ga-FAPI uptake was quantified by maximum standardised uptake value (SUVmax) and tissue-to-background ratio (TBRmax) correcting for blood-pool activity in the left ventricle. Comparisons between were assessed with one-way ANOVA with Tukey-Kramer post-hoc testing where significant differences were detected. A 2-sided p-value of <0.05 denoted statistical significance. Results Participants were predominantly middle-aged men with similar sized infarcts (peak plasma cardiac troponin concentrations and post-MI left ventricular ejection fraction) (Table). Blood pool tracer activity was also similar between groups. Focal myocardial 68Ga-FAPI uptake localised to areas of the infarct and peri-infarct zones on magnetic resonance late gadolinium enhancement imaging (Figure). Both myocardial SUVmax and TBRmax varied between infarcts of different ages, being highest in acute (TBRmax 4.1±1.2) and lowest in those with prior established MI (2.1±0.7, Table and Figure). Conclusions Fibrosis activity is greatest in the immediate aftermath of acute MI with a step-wise reduction in the weeks and years that follow. Fibrosis activity continues for many months and years after acute infarction.FigureTable

Sinonasal mucosal melanoma treatment response assessment to immune checkpoint inhibitors using hybrid positron emission tomography imaging

The purpose of this retrospective study was to investigate response of sinonasal mucosal melanoma (SMM) patients to treatment with immune checkpoint inhibitors (ICI), using hybrid PET imaging. Fifteen SMM patients underwent hybrid PET imaging before and three months after initiation of ICI. The disease-specific survival (DSS) was calculated. Quantitative PET parameters of the primary tumor and their association with DSS and therapy response were investigated. Nine of the fifteen (60%) patients responded to ICI therapy. Patients with therapy response depicted on hybrid PET imaging had better DSS than those without (p = 0.0058). Quantitative PET parameters of the initial PET harbored no association with DSS or therapy response. However, these findings lack of sufficient statistical power and must be interpreted with caution. The first restaging PET-imaging after ICI initiation can help stratify patients with regard to DSS.

The Impact of PET/MRI Fusion on the Diagnostic Imaging Industry

The multimodal imaging technique has gained the spotlight in the present era due to its striking and immense applications. It is the combination of two or more modalities that complement one another to yield detailed information. Indubitably, it is an emerging and crucial technique due to its broad clinical and research applications. The diagnostic techniques with the dual modality are aligned for obtaining molecular data. Positron emission tomography (PET) is a progressive imaging technique in nuclear medicine. To flourish in the imaging industry, PET was combined with computed tomography (CT), but the fusion of the two provides some challenges, such as less soft tissue contrast and inefficiency of acquisition in simultaneous mode. As a result, another hybrid imaging technology, PET and MRI (PET/MRI), has been developed to provide more soft tissue contrast and less radiation dose exposure, leading this technique to be used extensively despite its shortcomings. This review study discusses the fusion of PET/MRI, technical challenges for their combination, commercially available models, and clinical applications observed in the wide areas of oncology, the cardiovascular system, the central nervous system, pediatrics, and inflammatory diseases.

Restaging of rectal cancer with hybrid positron emission tomography magnetic resonance imaging after preoperative chemoradiotherapy.

This study determines the sensitivity and specificity of positron emission tomography/magnetic resonance imaging (PET/MRI) parameters in predicting treatment response in patients with localised rectal cancer who have undergone preoperative chemoradiotherapy (CRT). Patients with stage I-III adenocarcinoma of the rectum planned for preoperative CRT followed by surgery were recruited. Patients had PET/MRI scans at baseline and 6-8 weeks post-CRT. Functional MRI and PET parameters were assessed for their diagnostic accuracy for tumour regression grade (TRG). Nonparametric receiver operating characteristic analysis was employed to determine the area under the ROC curve (AUC), and the sensitivity and specificity of each quantile cut-off. A total of 31 patients were recruited, of whom 20 completed study protocol. All patients included had mid or lower rectal tumours. There were 16 patients (80%) with node-positive disease at presentation. The median time to surgery was 75.5 days (range 52-106 days). Histopathological assessment revealed 20% good responders (TRG 1/2), and the remaining 80% of patients had a poor response (TRG 3/4). When predicting good responders, the AUC values for percent maximum thickness reduction and percent apparent diffusion coefficient (ADC) change were 0.82 and 0.73, respectively. A maximum thickness reduction cut-off of >47% and a percent ADC change of >20% yielded a sensitivity and specificity of 75%/95% and 75%/73%, respectively. Parameters such as percent maximum thickness reduction and percent ADC change may be useful for predicting good responders in patients undergoing preoperative CRT for rectal cancer. Larger studies are warranted to establish the utility of PET/MRI in rectal cancer staging.

Time course of myocardial fibrosis activity following ST elevation myocardial infarction using 68Ga-FAPI PET/MR

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation - Prof Marc Dweck Senior Fellowship, and BHF Research Excellence Award 3 for Dr Anna K Barton. Background Myocardial fibrosis is a key healing response following myocardial infarction (MI). Although scar formation following MI is considered complete by 12 weeks, its exact time course is unknown. Fibroblast activation protein is a key factor in fibrogenesis that is expressed by activated fibroblasts in the myocardium following MI. Hybrid positron emission tomography and cardiovascular magnetic resonance (PET/MR) with radiolabelled fibroblast activation protein inhibitor (68Ga-FAPI) is an emerging method to measure in vivo fibrosis activity. Purpose To investigate the timing of myocardial fibrosis activity following ST-elevation MI using 68Ga-FAPI PET/MR Methods Twenty patients underwent multi-timepoint hybrid 68Ga-FAPI PET/MR <1, 2, 4, and 12 weeks following acute ST-elevation MI. They were compared to patients with prior established ST-elevation MI (>12 months) and healthy controls who underwent single-timepoint 68Ga-FAPI PET/MR to determine fibrosis activity in chronic infarcts and healthy myocardium respectively. All participants were imaged 30 min following administration of 100–200 MBq 68Ga-FAPI-04. Infarct zone 68Ga-FAPI uptake was quantified using tissue-to-background ratio (TBRmax) after correction for blood-pool activity in the left ventricle. Comparisons between timepoints for the acute MI group were assessed by ANOVA with repeated measures and post hoc Bonferroni correction, and between groups by two-tailed t-test. Results Participants were predominantly middle-aged men (Table). Focal 68Ga-FAPI uptake localised to areas of infarction within the infarct and peri-infarct zones on late gadolinium enhancement on magnetic resonance imaging (Figure). In acute MI, there was substantial uptake with consistent TBRmax values at weeks 1, 2 and 4 (Table and Figure). Though TBRmax values started to decline by week 12 they remained persistently elevated compared to prior established MI and healthy myocardium (Table). Participants with prior established MI had modestly increased 68Ga-FAPI uptake compared with the healthy myocardium of control participants (Table and Figure). Conclusions Intense myocardial fibrosis activity is observed in the infarct and peri-infarct zones throughout the first month following ST-elevation MI. Although this starts to decline by 12 weeks, it remains markedly elevated even several years after myocardial infarction, indicating that low-level chronic fibroblast activity is a feature of established MI.

Thalamic‐insomnia phenotype in genetic E200K Creutzfeldt‐Jakob disease: A PET/MRI study

AbstractBackgroundInsomnia and thalamic involvement are hallmarks of fatal familial insomnia; however, it was occasionally reported that genetic E200K Creutzfeldt‐Jakob disease (CJD) patients had also manifested thalamic‐insomnia phenotype. The study aimed to explore the clinical and neuroimage characteristics of genetic E200K CJD by comprehensive neuroimage analysis.MethodsSix genetic CJD patients carried Glu to Lys change at codon 200 (E200K) mutations on prion protein gene (PRNP), thirteen sporadic CJD (sCJD), and twenty‐two age‐ and sex‐matched normal controls were enrolled in the study. All participants completed hybrid positron emission tomography/ magnetic resonance imaging (PET/MRI) examinations. The high signal was visually inspected on diffusion weighted imaging (DWI) sequence. 18F‐fluorodeoxyglucose positron emission tomography (18F‐FDG‐PET) and structural images were quantitively analyzed by statistically parameter mapping (SPM). Clinical and image characteristics are compared between genetic E200K CJD patients and sporadic CJD patients.ResultsThere was no group difference in age (49.0±7.1 versus 55.0±4.9 versus 52.7±7.3, p = 0.193) and gender (3/3 versus 4/9 versus 11/11, p = 0.513) between genetic E200K CJD, sCJD, and normal controls. Insomnia was the main complaint in the genetic E200K CJD patients’ group (4/2 versus 1/12, p = 0.007). Hyperintensity, hypometabolism but not predominant atrophy of the thalamus was found by visual inspection in genetic E200K CJD patients. A decreased trend was found on gray matter volume (uncorrected p<0.0001) and metabolism (FWE corrected) of the thalamus in genetic E200K patients.ConclusionThe clinical and image characteristics of genetic E200K CJD mimic fatal familial insomnia, manifested as a thalamic‐insomnia phenotype, indicating some specific underlying pathological changes might exist in E200K mutations. PET measurement is a sensitive approach to help identify the functional changes of the thalamus in prion disease.

Arrhythmic Mitral Valve Prolapse With Only Mild or Moderate Mitral Regurgitation: Characterization of Myocardial Substrate

BackgroundSustained ventricular tachycardia and sudden cardiac death due to degenerative mitral valve prolapse (MVP) can occur in the absence of severe mitral regurgitation (MR). A significant percentage of patients with MVP-related sudden death do not have any evidence of replacement fibrosis, suggesting other unrecognized proarrhythmic factors may place these patients at risk. ObjectivesThis study aims to characterize myocardial fibrosis/inflammation and ventricular arrhythmia complexity in patients with MVP and only mild or moderate MR. MethodsProspective observational study of patients with MVP and only mild or moderate MR underwent ventricular arrhythmia characterization and hybrid positron emission tomography (PET)/magnetic resonance imaging (MRI). Coregistered hybrid 18F-fluorodeoxyglucose (18F-FDG)–PET and MRI late gadolinium enhancement images were assessed and categorized. Recruitment occurred in the cardiac electrophysiology clinic. ResultsIn 12 patients with degenerative MVP with only mild or moderate MR, of which a majority had complex ventricular ectopy (n = 10, 83%), focal (or focal-on-diffuse) uptake of 18F-FDG (PET-positive) was detected in 83% (n = 10) of patients. Three-quarters of the patients (n = 9, 75%) had FDG uptake that coexisted with areas of late gadolinium enhancement (PET/MRI-positive). Abnormal T1, T2 and extracellular volume (ECV) values were observed in 58% (n = 7), 25% (n = 3), and 16% (n = 2), respectively. ConclusionsMost patients with degenerative MVP, ventricular ectopy, and mild or moderate MR show myocardial inflammation that is concordant with myocardial scar. Further study is needed to determine whether these findings contribute to the observation that most MVP-related sudden deaths occur in patients with less than severe MR.

Relevance of 18F-DOPA visual and semi-quantitative PET metrics for the diagnostic of Parkinson disease in clinical practice: a machine learning-based inference study

PurposeTo decipher the relevance of visual and semi-quantitative 6-fluoro-(18F)-L-DOPA (18F-DOPA) interpretation methods for the diagnostic of idiopathic Parkinson disease (IPD) in hybrid positron emission tomography (PET) and magnetic resonance imaging.Material and methodsA total of 110 consecutive patients (48 IPD and 62 controls) with 11 months of median clinical follow-up (reference standard) were included. A composite visual assessment from five independent nuclear imaging readers, together with striatal standard uptake value (SUV) to occipital SUV ratio, striatal gradients and putamen asymmetry-based semi-quantitative PET metrics automatically extracted used to train machine learning models to classify IPD versus controls. Using a ratio of 70/30 for training and testing sets, respectively, five classification models—k-NN, LogRegression, support vector machine, random forest and gradient boosting—were trained by using 100 times repeated nested cross-validation procedures. From the best model on average, the contribution of PET parameters was deciphered using the Shapley additive explanations method (SHAP). Cross-validated receiver operating characteristic curves (cv-ROC) of the most contributive PET parameters were finally estimated and compared.ResultsThe best machine learning model (k-NN) provided final cv-ROC of 0.81. According to SHAP analyses, visual PET metric was the most important contributor to the model overall performance, followed by the minimum between left and right striatal to occipital SUV ratio. The 10-time cv-ROC curves of visual, min SUVr or both showed quite similar performance (mean area under the ROC of 0.81, 0.81 and 0.79, respectively, for visual, min SUVr or both).ConclusionVisual expert analysis remains the most relevant parameter to predict IPD diagnosis at 11 months of median clinical follow-up in 18F-FDOPA. The min SUV ratio appears interesting in the perspective of simple semi-automated diagnostic workflows.

Hybrid positron emission tomography and magnetic resonance imaging in cardiac sarcoidosis diagnosis: a pilot experience

Hybrid positron emission tomography and magnetic resonance imaging in cardiac sarcoidosis diagnosis: a pilot experience

The Principle and State-of-Art Facilities for PET

Since the late 20th century, Positron Emission Tomography (PET) scanners and their hybrid scanners (PET/CT and PET/MRI) offer a path to detect cancer. In this research, the PET scan will be introduced and discussed in multiple dimensions, mainly to explain the principle of PET scan, the state-of-art of PET scans, and the future of PET scans. According to the analysis, from the time that the PET scanner is invented, it not only had a better image quality but also had more functions. It is believed that an intelligent non-radioactive scanner will be achieved in the future due to the development of MRI and artificial intelligence. The main reason for conducting this research is to understand the mechanisms of PET as well as investigate the way to improve the technology itself to avoid the limitations it poses. Overall, these results shed light on guiding further exploration of the next generation of PET scans (e.g., Hybrid PET machines and machine learning).

Abstract 9764: Simultaneous Assessment of Coronary Flow Reserve and Left Ventricular Strain During Vasodilator Stress Measured by 13 N-ammonia Positron Emission Tomography/Magnetic Resonance Imaging

Introduction: Hybrid positron emission tomography (PET)/magnetic resonance imaging (MRI) is able to yield important information regarding molecular and functional imaging in a one-stop examination. The aim of this study was to investigate the relationship between coronary flow reserve (CFR) and left ventricular longitudinal strain (LVLS) using simultaneous acquisitions on hybrid 13 N-ammonia PET/MRI. Methods: Thirty-eight patients with suspected coronary artery disease (CAD) who underwent 13 N-ammonia PET/MRI were enrolled. Vasodilator stress was induced by intravenous injection of adenosine. CFR was calculated from dynamic acquisition of 13 N-ammonia PET. LVLS was evaluated by feature-tracked MRI. Myocardial flow reserve (MFR) and LVLS values were based on a 17-segment model and three coronary territories, left anterior descending artery (LAD), left circumflex artery (LCx), and right coronary artery (RCA). Results: We analyzed 577 myocardial segments in the left ventricle. LVLS under vasodilator stress was significantly increased compared with LVLS at rest in myocardial segments with MFR ≥2.0 (P<0.01), whereas there were no changes between LVLS under stress and LVLS at rest in the segments with MFR < 2.0 (P=0.24). Similarly, regional values of LVLS under vasodilator stress were significantly increased compared with those measured at rest in the coronary territories of LAD (P<0.01), LCx (P<0.01), and RCA (P<0.01) with MFR ≥ 2.0, whereas there were no differences between LVLS at rest and LVLS under stress in those territories with CFR < 2.0 (P=0.45). These data revealed that left ventricular strain under vasodilator stress was impaired in segments with lower CFR. Conclusion: Simultaneous assessment of regional CFR and LV strain was feasible using by 13 N-ammonia PET/MRI. 13 N-ammonia PET/MRI was able to detect not only impaired CFR but also morphological abnormalities, which may improve diagnostic and predictive capacity in patients with CAD.

Comparing Radiation Dose Between Contrast-Enhanced and Non-Contrast-Enhanced CTAC Acquisition in 18F-FDG-PET/CT Examination

Introduction: Hybrid Positron Emission Tomography with Computed Tomography (PET/CT) imaging is well established in the oncology setting. However, in the current cancer diagnostic imaging approach in Malaysia patients need separate CT and PET/CT examinations for morphologic and physiologic cancer staging, respectively, as PET/CT is unable to produce images with optimum diagnostic quality. Therefore, introducing contrast media into CT attenuation correction (CTAC) acquisition to increase image quality have raised concerns on heightened radiation exposure. This study aimed to verify the amount of external radiation exposure irradiated to the patient converging to the scanning protocol implemented in whole-body (WB) 18F-FDG-PET/CT examination. Methods: A retrospective study was conducted to determine the radiation dose delivered during CTAC acquisition of 18F-FDG-PET/CT examination at three hospitals providing PET/CT imaging services in Penang State. The implemented scanning protocols and parameters, and the effective dose received by the patient were analysed based on dose length product (DLP) and CTDIvol reported by the scanner. Results: CTAC of WB 18F-FDG-PET/CT imaging was executed as either non-contrast (NC-CTAC) or contrast-enhanced (CE-CTAC). CE-CTAC produced a 250% higher radiation dose compared to NC-CTAC. The scanning parameter differences that significantly contributed to increased radiation dose were the tube current and pitch value. Conclusion: CE-CTAC delivered a higher radiation dose than NC-CTAC acquisition in WB 18F-FDG PET/CT imaging due to different mAs and pitch as scanning parameters. Malaysian Journal of Medicine and Health Sciences (2022) 18(SUPP15): 132-139. doi:10.478

Crossed cerebellar diaschisis-related supratentorial hemodynamic and metabolic status measured by PET/MR in assessing postoperative prognosis in chronic ischemic cerebrovascular disease patients with bypass surgery

ObjectiveCerebral ischemic status is an indicator of bypass surgery. Both hemodynamics and glucose metabolism are significant factors for evaluating cerebral ischemic status. The occurrence of crossed cerebellar diaschisis (CCD) is influenced by the degree of supra-tentorial perfusion and glucose metabolism reduction. This study aimed to investigate the relationship between the CCD-related supra-tentorial blood flow and metabolic status before bypass surgery in patients with chronic and symptomatic ischemic cerebrovascular disease and the prognosis of surgery.MethodsTwenty-four participants with chronic ischemic cerebrovascular disease who underwent hybrid positron emission tomography (PET)/magnetic resonance (MR) before bypass surgery were included. Arterial spin labeling (ASL)-MR and FDG-PET were used to measure blood flow and metabolism, respectively. The PET images were able to distinguish CCD. The supratentorial asymmetry index (AI) and volume in the decreased blood flow region, decreased metabolism region and co-decreased region on the affected side, except for the infarct area, were respectively obtained before bypass surgery. The neurological status was determined using the National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS) scores. Differences between CCD-positive (CCD +) and CCD-negative (CCD−) groups were investigated.ResultsFourteen (58%) of the 24 patients were diagnosed as CCD +. Before surgery, the NIHSS and mRS scores of the CCD + were significantly higher than those of the CCD− (1.0(1.0) vs. 0.0(1.0), P = 0.013; 1.0(1.5) vs. 0.0(1.5), P = 0.048). After the surgery, the NIHSS and mRS scores of the CCD + showed a significant decrease (0.0(1.0) to 0.0(0.0), P = 0.011; 0.0(0.5) to 0.0(0.0), P = 0.008). Significant differences were observed in the supra-tentorial decreased metabolism region (all Ps ≤ 0.05) between the CCD + and CCD− groups, but no differences were observed in the preprocedural decreased supratentorial blood flow region (P > 0.05). The preprocedural NIHSS score was strongly correlated with the metabolism AI value in the decreased metabolism region (r = 0.621, P = 0.001) and the co-decreased region (r = 0.571, P = 0.004).ConclusionsSupratentorial blood flow and metabolism are important indicators of CCD. This study showed that CCD + patients benefited more from bypass surgery than CCD− patients. Staging based on CCD-related supra-tentorial blood flow and metabolic status by hybrid PET/MR may help to personalize treatment.

Potential role of hybrid positron emission tomography in pre-operative assessment of primary salivary gland carcinomas.

The added value of hybrid positron emission tomography is increasingly recognised in head and neck cancer. However, its potential role in salivary gland carcinomas has been scarcely investigated. A consecutive cohort of 45 salivary gland carcinoma patients who underwent pre-therapeutic hybrid positron emission tomography and surgical resection was reviewed. This study investigated whether maximum standardised uptake value correlated with tumour phenotype. Tumours of high-grade disease on histology (salivary duct carcinoma, carcinoma ex pleomorphic adenoma) had higher maximum standardised uptake value (Kruskal-Wallis test, p = 0.011) than low-grade tumours (adenoid cystic carcinoma and acinic cell carcinoma). Patients with pathologically confirmed node-positive disease had significantly higher maximum standardised uptake value of the primary tumour than patients with pathologically confirmed node-negative disease (Kruskal-Wallis test, p = 0.012). Maximum standardised uptake value of the primary tumour may guide clinical decision-making in patients with salivary gland carcinomas, as a high maximum standardised uptake value is associated with high-grade tumour histology and the presence of lymph node metastases. Clinicians may consider more aggressive surgery for these patients.

Prognostic Value of Hybrid PET/MR Imaging in Patients with Differentiated Thyroid Cancer.

Simple SummaryHybrid positron emission tomography (PET)/magnetic resonance (MR) is an emerging imaging modality with great potential to provide complementary data acquired at the same time, under the same physiological conditions. We evaluated the prognostic value of hybrid 18F-fluorodeoxyglucose (FDG) PET/MR in patients with differentiated thyroid cancer (DTC) who underwent total thyroidectomy and radioactive iodine therapy for suspicion of disease relapse. Our findings suggest that hybrid PET/MR imaging may have the potential to improve the information content of one modality with the other and would offer new opportunities in patients with DTC. However, there is need of more clinical studies to understand the additional value of 18F-FDG PET/MR in patients with DTC.Background: Hybrid positron emission tomography (PET)/magnetic resonance (MR) is an emerging imaging modality with great potential to provide complementary data acquired at the same time, under the same physiological conditions. The aim of this study was to evaluate the prognostic value of hybrid 18F-fluorodeoxyglucose (FDG) PET/MR in patients with differentiated thyroid cancer (DTC) who underwent total thyroidectomy and radioactive iodine therapy for suspicion of disease relapse. Methods: Between November 2015 and February 2017, 55 patients underwent hybrid 18F-FDG PET/MR. Assessment of positive MR was made considering all sequences in terms of malignancy based on the morphological T2-weighted features and the presence of restricted diffusivity on diffusion-weighted imaging images and both needed to be positive on the same lesion. Both foci with abnormal 18F-FDG uptake, which corresponded to tissue abnormalities on the MR, and tracer accumulation, which did not correspond to normal morphological structures, were considered positive. Results: During follow-up (mean 42 ± 27 months), 29 patients (53%) had disease recurrence. In the Cox univariate regression analysis age, serum Tg level ≥ 2 ng/mL, positive short tau inversion recovery (STIR), and positive PET were significant predictors of DTC recurrence. Kaplan–Meier survival analyses showed that patients with Tg ≥ 2 ng/mL had poorer outcomes compared to those with serum Tg level < 2 ng/mL (p < 0.05). Similarly, patients with positive STIR and positive PET had a worst outcome compared to those with negative STIR (p < 0.05) and negative PET (p < 0.005). Survival analysis performed in the subgroup of 36 subjects with Tg level ≥ 2 ng/mL revealed that patients with positive PET had a worst outcome compared to those with negative PET (p < 0.05). Conclusions: Age, serum Tg level ≥ 2 ng/mL, positive STIR, and positive 18F-FDG PET were significant predictors of DTC recurrence. However, the serum Tg level was the only independent predictor of DTC. Hybrid PET/MR imaging may have the potential to improve the information content of one modality with the other and would offer new opportunities in patients with DTC. Thus, further studies in a larger patient population are needed to understand the additional value of 18F-FDG PET/MR in patients with DTC.

The Impact of PIK3R1 Mutations and Insulin-PI3K-Glycolytic Pathway Regulation in Prostate Cancer.

Oncogenic alterations of the PI3K/AKT pathway occur in >40% of patients with metastatic castration-resistant prostate cancer, predominantly via PTEN loss. The significance of other PI3K pathway components in prostate cancer is largely unknown. Patients in this study underwent tumor sequencing using the MSK-IMPACT clinical assay to capture single-nucleotide variants, insertions, and deletions; copy-number alterations; and structural rearrangements, or were profiled through The Cancer Genome Atlas. The association between PIK3R1 alteration/expression and survival was evaluated using univariable and multivariable Cox proportional-hazards regression models. We used the siRNA-based knockdown of PIK3R1 for functional studies. FDG-PET/CT examinations were performed with a hybrid positron emission tomography (PET)/CT scanner for some prostate cancer patients in the MSK-IMPACT cohort. Analyzing 1,417 human prostate cancers, we found a significant enrichment of PIK3R1 alterations in metastatic cancers compared with primary cancers. PIK3R1 alterations or reduced mRNA expression tended to be associated with worse clinical outcomes in prostate cancer, particularly in primary disease, as well as in breast, gastric, and several other cancers. In prostate cancer cell lines, PIK3R1 knockdown resulted in increased cell proliferation and AKT activity, including insulin-stimulated AKT activity. In cell lines and organoids, PIK3R1 loss/mutation was associated with increased sensitivity to AKT inhibitors. PIK3R1-altered patient prostate tumors had increased uptake of the glucose analogue 18F-fluorodeoxyglucose in PET imaging, suggesting increased glycolysis. Our findings describe a novel genomic feature in metastatic prostate cancer and suggest that PIK3R1 alteration may be a key event for insulin-PI3K-glycolytic pathway regulation in prostate cancer.

Simultaneous assessment of microcalcifications and morphological criteria of vulnerability in carotid artery plaque using hybrid 18F-NaF PET/MRI

BackgroundPrevious studies have suggested the role of microcalcifications in plaque vulnerability. This exploratory study sought to assess the potential of hybrid positron-emission tomography (PET)/magnetic resonance imaging (MRI) using 18F-sodium fluoride (18F-NaF) to check simultaneously 18F-NaF uptake, a marker of microcalcifications, and morphological criteria of vulnerability. Methods and resultsWe included 12 patients with either recently symptomatic or asymptomatic carotid stenosis. All patients underwent 18F-NaF PET/MRI. 18F-NaF target-to-background ratio (TBR) was measured in culprit and nonculprit (including contralateral plaques of symptomatic patients) plaques as well as in other arterial walls. Morphological criteria of vulnerability were assessed on MRI. Mineral metabolism markers were also collected. 18F-NaF uptake was higher in culprit compared to nonculprit plaques (median TBR 2.6 [2.2-2.8] vs 1.7 [1.3-2.2]; P = 0.03) but was not associated with morphological criteria of vulnerability on MRI. We found a positive correlation between 18F-NaF uptake and calcium plaque volume and ratio but not with circulating tissue-nonspecific alkaline phosphatase (TNAP) activity and inorganic pyrophosphate (PPi) levels. 18F-NaF uptake in the other arterial walls did not differ between symptomatic and asymptomatic patients. Conclusions18F-NaF PET/MRI may be a promising tool for providing additional insights into the plaque vulnerability.