Significant dose reduction is feasible in FDG PET/CT protocols without compromising diagnostic quality

Production of carbon-11 for PET preclinical imaging using a high-repetition rate laser-driven proton source

Most advanced medical imaging techniques, such as positron-emission tomography (PET), require tracers that are produced in conventional particle accelerators. This paper focuses on the evaluation of a potential alternative technology based on laser-driven ion acceleration for the production of radioisotopes for PET imaging. We report for the first time the use of a high-repetition rate, ultra-intense laser system for the production of carbon-11 in multi-shot operation. Proton bunches with energies up to 10-14 MeV were systematically accelerated in long series at pulse rates between 0.1 and 1 Hz using a PW-class laser. These protons were used to activate a boron target via the11 B(p,n)11 C nuclear reaction. A peak activity of 234 kBq was obtained in multi-shot operation with laser pulses with an energy of 25 J. Significant carbon-11 production was also achieved for lower pulse energies. The experimental carbon-11 activities measured in this work are comparable to the levels required for preclinical PET, which would be feasible by operating at the repetition rate of current state-of-the-art technology (10 Hz). The scalability of next-generation laser-driven accelerators in terms of this parameter for sustained operation over time could increase these overall levels into the clinical PET range.

Impact of simulated reduced injected dose on the assessment of amyloid PET scans

PURPOSE

To investigate the impact of reduced injected doses on the quantitative and qualitative assessment of the amyloid PET tracers [18F]flutemetamol and [18F]florbetaben.

METHODS

Cognitively impaired and unimpaired individuals (N = 250, 36% Aβ-positive) were included and injected with [18F]flutemetamol (N = 175) or [18F]florbetaben (N = 75). PET scans were acquired in list-mode (90-110 min post-injection) and reduced-dose images were simulated to generate images of 75, 50, 25, 12.5 and 5% of the original injected dose. Images were reconstructed using vendor-provided reconstruction tools and visually assessed for Aβ-pathology. SUVRs were calculated for a global cortical and three smaller regions using a cerebellar cortex reference tissue, and Centiloid was computed. Absolute and percentage differences in SUVR and CL were calculated between dose levels, and the ability to discriminate between Aβ- and Aβ + scans was evaluated using ROC analyses. Finally, intra-reader agreement between the reduced dose and 100% images was evaluated.

RESULTS

At 5% injected dose, change in SUVR was 3.72% and 3.12%, with absolute change in Centiloid 3.35CL and 4.62CL, for [18F]flutemetamol and [18F]florbetaben, respectively. At 12.5% injected dose, percentage change in SUVR and absolute change in Centiloid were < 1.5%. AUCs for discriminating Aβ- from Aβ + scans were high (AUC ≥ 0.94) across dose levels, and visual assessment showed intra-reader agreement of > 80% for both tracers.

CONCLUSION

This proof-of-concept study showed that for both [18F]flutemetamol and [18F]florbetaben, adequate quantitative and qualitative assessments can be obtained at 12.5% of the original injected dose. However, decisions to reduce the injected dose should be made considering the specific clinical or research circumstances.

Revising and exploring the variations in methodologies for establishing the diagnostic reference levels for paediatric PET/CT imaging

PET-computed tomography (PET/CT) is a hybrid imaging technique that combines anatomical and functional information; to investigate primary cancers, stage tumours, and track treatment response in paediatric oncology patients. However, there is debate in the literature about whether PET/CT could increase the risk of cancer in children, as the machine is utilizing two types of radiation, and paediatric patients have faster cell division and longer life expectancy. Therefore, it is essential to minimize radiation exposure by justifying and optimizing PET/CT examinations and ensure an acceptable image quality. Establishing diagnostic reference levels (DRLs) is a crucial quantitative indicator and effective tool to optimize paediatric imaging procedures. This review aimed to distinguish and acknowledge variations among published DRLs for paediatric patients in PET/CT procedures. A search of relevant articles was conducted using databases, that is, Embase, Scopus, Web of Science, and Medline, using the keywords: PET-computed tomography, computed tomography, PET, radiopharmaceutical, DRL, and their synonyms. Only English and full-text articles were included, with no limitations on the publication year. After the screening, four articles were selected, and the review reveals different DRL approaches for paediatric patients undergoing PET/CT, with primary variations observed in patient selection criteria, reporting of radiation dose values, and PET/CT equipment. The study suggests that future DRL methods for paediatric patients should prioritize data collection in accordance with international guidelines to better understand PET/CT dose discrepancies while also striving to optimize radiation doses without compromising the quality of PET/CT images.

The potential advantages and workflow challenges of long axial field of view PET/CT

Recently developed Long (≥100 cm) axial field of view (AFOV) PET/CT scanners are capable of producing images with higher signal-to-noise ratio, or performing faster whole-body acquisitions, or scanning with lower radiation dose to the patient, compared with conventional PET/CT scanners. These benefits, which arise due to their substantially higher, by more than an order of magnitude, geometric efficiency, have been well described in the recent literature. The introduction of Long AFOV PET/CT technology into the clinic also has important implications for the design and workflow of PET/CT facilities and their effects on radiation exposure to staff and patients. Maximising the considerable benefits of this technology requires a thorough understanding of the relationships between these factors to optimise workflows while appropriately managing radiation exposure. This article reviews current knowledge on PET/CT facility design, workflows and their effects on radiation exposure, identifies gaps in the literature and discusses the challenges that need to be considered with the introduction of Long AFOV PET/CT into the clinic.

Optimization of the Acquisition Time and Injected Dose of 18 F-Fluorodeoxyglucose Based on Patient Specifications for High-Sensitive Positron Emission Tomography/Computed Tomography Scanner

Background  This study was aimed to optimize the fluorodeoxyglucose (FDG)-administered dose and scan time based on patient specifications using a highly sensitive five-ring bismuth germanium oxide (BGO)-based positron emission tomography/computed tomography (PET/CT) scanner (Discovery IQ). Methods  We retrospectively analyzed 101 whole-body 18 F-FDG PET/CT images. Patient data were reconstructed using ordered subset expectation maximization with resolution recovery algorithms (OSEM + SharpIR). Signal-to-noise ratio (SNR) was calculated for each patient, standardized to SNR norm , and plotted against three body index parameters (weight, body mass index, and lean body mass). Two professional physicians blindly examined image quality at different patient time per bed positions to determine the minimum acceptable quality. To select images of acceptable quality, the noise index parameter was also measured. A new dose-time product (DTP) was established for each patient, and a predicted injected dose was assumed. Results  We found an almost linear association between patient weight and normalized SNR, and patient weight had the highest R 2 in the fitting. The redesigned DTP can reduce results by approximately 74 and 38% compared with ordinary DTP for 80- and 160-s scan durations. The new dose regimen formula was found to be DTP =  c/t × m 1.24 , where m is the patient weight, t is the scan time per bed position, and c is 1.8 and 4.3 for acceptable and higher confidence states, respectively, in Discovery IQ PET/CT. Conclusion  Patient weight is the best clinical parameter for the implementation of 18 F-FDG PET/CT image quality assessment. A new dose-time regimen based on body weight was proposed for use in highly sensitive five-ring BGO PET-CT scanners to significantly reduce the injection dose and scan times while maintaining sufficient image quality for diagnosis.

PET/CT May Assist in Avoiding Pointless Thyroidectomy in Indeterminate Thyroid Nodules: A Narrative Review

Indeterminate thyroid nodules (ITN) are commonly encountered among the general population, with a malignancy rate of 10 to 40%. However, many patients may be overtreated with futile surgery for benign ITN. To avoid unnecessary surgery, PET/CT scan is a possible alternative to help differentiate between benign and malignant ITN. In this narrative review, the major results and limitations of the most recent studies on PET/CT efficacy (from PET/CT visual assessment to quantitative PET parameters and recent radiomic features analysis) and on cost-effectiveness (compared to other alternatives (such as surgery)) are presented. PET/CT can reduce futile surgery with visual assessment (around 40%; if ITN ≥ 10 mm). Moreover, PET/CT conventional parameters and radiomic features extracted from PET/CT imaging can be associated together in a predictive model to rule out malignancy in ITN, with a high NPV (96%) when certain criteria are met. Even though promising results were obtained in these recent PET/CT studies, further studies are needed to enable PET/CT to become the definitive diagnostic tool once a thyroid nodule is identified as indeterminate.

Ultra-low-dose CT reconstructed with the artificial intelligence iterative reconstruction algorithm (AIIR) in 18F-FDG total-body PET/CT examination: a preliminary study

PURPOSE

To investigate the feasibility of ultra-low-dose CT (ULDCT) reconstructed with the artificial intelligence iterative reconstruction (AIIR) algorithm in total-body PET/CT imaging.

METHODS

The study included both the phantom and clinical parts. An anthropomorphic phantom underwent CT imaging with ULDCT (10mAs) and standard-dose CT (SDCT) (120mAs), respectively. ULDCT was reconstructed with AIIR and hybrid iterative reconstruction (HIR) (expressed as ULDCT-AIIR_phantom and ULDCT-HIR_phantom), respectively, and SDCT was reconstructed with HIR (SDCT-HIR_phantom) as control. In the clinical part, 52 patients with malignant tumors underwent the total-body PET/CT scan. ULDCT with AIIR (ULDCT-AIIR) and HIR (ULDCT-HIR), respectively, was reconstructed for PET attenuation correction, followed by the SDCT reconstructed with HIR (SDCT-HIR) for anatomical location. PET/CT images' quality was qualitatively assessed by two readers. The CT_mean, as well as the CT standard deviation (CT_sd), SUV_max, SUV_mean, and the SUV standard deviation (SUV_sd), was recorded. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared.

RESULTS

The image quality of ULDCT-HIR_phantom was inferior to the SDCT-HIR_phantom, but no significant difference was found between the ULDCT-AIIR_phantom and SDCT-HIR_phantom. The subjective score of ULDCT-AIIR in the neck, chest and lower limb was equivalent to that of SDCT-HIR. Besides the brain and lower limb, the change rates of CT_mean in thyroid, neck muscle, lung, mediastinum, back muscle, liver, lumbar muscle, first lumbar spine and sigmoid colon were -2.15, -1.52, 0.66, 2.97, 0.23, 8.91, 0.06, -4.29 and 8.78%, respectively, while all CT_sd of ULDCT-AIIR was lower than that of SDCT-HIR. Except for the brain, the CNR of ULDCT-AIIR was the same as the SDCT-HIR, but the SNR was higher. The change rates of SUV_max, SUV_mean and SUV_sd were within [Formula: see text] 3% in all ROIs. For the lesions, the SUV_max, SUV_sd and TBR showed no significant difference between PET-AIIR and PET-HIR.

CONCLUSION

The SDCT-HIR could not be replaced by the ULDCT-AIIR at date, but the AIIR algorithm decreased the image noise and increased the SNR, which can be implemented under special circumstances in PET/CT examination.

[18F] Sodium Fluoride Dose Reduction Enabled by Digital Photon Counting PET/CT for Evaluation of Osteoblastic Activity

The aim of the study was to assess the quality and reproducibility of reducing the injected [¹⁸F] sodium fluoride ([¹⁸F]NaF) dose while maintaining diagnostic imaging quality in bone imaging in a preclinical skeletal model using digital photon counting PET (dPET) detector technology. Beagles (n = 9) were administered three different [¹⁸F]NaF doses: 111 MBq (n = 5), 20 MBq (n = 5), and 1.9 MBq (n = 9). Imaging started ≃45 min post-injection for ≃30 min total acquisition time. Images were reconstructed using Time-of-Flight, ultra-high definition (voxel size of 1 × 1 × 1 mm³), with 3 iterations and 3 subsets. Point spread function was modeled and Gaussian filtering was applied. Skeleton qualitative and quantitative molecular image assessment was performed. The overall diagnostic quality of all images scored excellent (61%) and acceptable (39%) by all the reviewers. [¹⁸F]NaF SUV_mean showed no statistically significant differences among the three doses in any of the region of interest assessed. This study demonstrated that a 60-fold [¹⁸F]NaF dose reduction was not significantly different from the highest dose, and it had not significant effect on overall image quality and quantitative accuracy. In the future, ultra-low dose [¹⁸F]NaF dPET/CT imaging may significantly decrease PET radiation exposure to preclinical subjects and personnel.

Radiobiological risks in terms of effective dose and organ dose from 18F-FDG whole-body PET/CT procedures

Introduction

Integrated Positron Emission Tomography (PET) with Computerized tomography (CT) (PET/CT) are widely used to diagnose, stage and track human diseases during whole body scanning. Multi-modality imaging is an interesting area of research that aims at acquiring united morphological-functional image information for accurate diagnosing and staging of the disease. However, PET/CT procedure accompanied with high radiation dose from CT and administered radioactivity. The aim of the present study was to estimate the patients' dose from ¹⁸F-fluorodeoxyglucose imaging (18F-FDG) hybrid PET/CT whole body scan.

Materials and methods

RADAR (Radiation Dose Assessment Resource) software was used to estimate the effective dose for 156 patients (110 (70.5%)) males and 46 (39.5%) female) examined using Discovery PET/CT 710, GE Medical Systems installed at Kuwait Cancer Control Center (KCCC).

Results

The effective dose results presented in this PET/CT study ranged from (1.56-9.94 mSv). The effective dose was calculated to be 3.88 mSv in females and 3.71 mSv in males. The overall breast (female), lung, liver, kidney and thyroid were 7.4, 7.2, 5.2, 4, 3 and 2.9, respectively.For females, the body mass index (BMI) was 28.49 kg/m² and for males it was 26.50 kg/m² which showed overweight values for both genders. Conclusions: The findings indicate that the effective dose of 18F-FDG in both male and female patients was not substantially different. The study suggested that the risk-benefit proportions of any ¹⁸F-FDG whole body PET/CT scan should be clarified and carefully weighed. Patient's doses are lower compared with previous studies.

Correlation between 18F-FDG dosage and SNR on various BMI patient groups tested in NEMA IEC PET phantom

The present study was conducted to determine quantitatively the correlation between injected radiotracer and signal-to-noise ratio (SNR) based on differences in physiques and stages of cancer. Eight different activities were evaluated with modelled National Electrical Manufacturers Association (NEMA) of the International Electrotechnical Commission (IEC) PET's phantom with nine different tumour-to-background ratio (TBR). The findings suggest that the optimal value of dosage is required for all categories of patients in the early stages of cancer diagnosis.

Cumulative radiation doses from recurrent PET/CT examinations

Positron emission tomography (PET–CT) is an essential imaging modality for the management of various diseases. Increasing numbers of PET–CT examinations are carried out across the world and deliver benefits to patients; however, there are concerns about the cumulative radiation doses from these examinations in patients. Compared to the radiation exposure delivered by CT, there have been few reports on the frequency of patients with a cumulative effective radiation dose of ≥100 mSv from repeated PET–CT examinations. The emerging dose tracking system facilitates surveys on patient cumulative doses by PET–CT because it can easily wrap up exposure doses of PET radiopharmaceuticals and CT. Regardless of the use of a dose tracking system, implementation of justification for PET–CT examinations and utilisation of dose reduction measures are key issues in coping with the cumulative dose in patients. Despite all the advantages of PET/MRI such as eliminating radiation exposure from CT and providing good tissue contrast in MRI, it is expensive and cannot be introduced at every facility; thus, it is still necessary to utilise PET–CT with radiation reduction measures in most clinical situations.

Feasibility of equivalent performance of 3D TOF [18F]-FDG PET/CT with reduced acquisition time using clinical and semiquantitative parameters

Background

High-performance time-of-flight (TOF) positron emission tomography (PET) systems have the capability for rapid data acquisition while preserving diagnostic image quality. However, determining a reliable and clinically applicable cut-off of the acquisition time plays an important role in routine practice. This study aimed to assess the diagnostic equivalence of short acquisition time of 57 with routine 75 seconds per bed position (s/BP) of [¹⁸F]-fluoro-deoxy-glucose (FDG) PET.

Phantom studies applying EARL criteria suggested the feasibility of shortened acquisition time in routine clinical imaging by 3D TOF PET/CT scanners. Ninety-six patients with melanoma, lung or head and neck cancer underwent a standard whole-body, skull base-to-thigh or vertex-to-thigh [¹⁸F]-FDG PET/CT examination using the 3D TOF Ingenuity TF PET/CT system (Philips, Cleveland, OH). The [¹⁸F]-FDG activity applied was equal to 4MBq per kg body weight. Retrospectively, PET list-mode data were used to calculate a second PET study per patient with a reduced acquisition time of 57 s instead of routine 75 s/BP. PET/CT data were reconstructed using a 3D OSEM TOF algorithm. Blinded patient data were analysed by two nuclear medicine physicians. The number of [¹⁸F]-FDG-avid lesions per body region (head&neck, thorax, abdomen, bone, extremity) and image quality (grade 1–5) were evaluated. Semiquantitative analyses were performed by standardized uptake value (SUV) measurements using 3D volume of interests (VOI). The visual and semiquantitative diagnostic equivalence of 214 [¹⁸F]-FDG-avid lesions were analysed in the routine standard (75 s/BP) as well as the calculated PET/CT studies with short acquisition time. Statistical analyses were performed by equivalence testing and Bland–Altman plots.

Results

Lesion detection rate per patient’s body region agreed in > 98% comparing 57 s/BP and 75 s/BP datasets. Overall image quality was determined as equal or superior to 75 s in 80% and 69%, respectively. In the semiquantitative lesion-based analyses, a significant equivalence was found between the 75 s/BP and 57 s/BP PET/CT images both for SUV_max (p = 0.004) and SUV_mean (p = 0.003).

Conclusion

The results of this study demonstrate significant clinical and semiquantitative equivalence between short acquisition time of 57 s/BP and standard 75 s/BP 3D TOF [¹⁸F]-FDG PET/CT scanning, which may improve the patient’s workflow in routine practice.

The role of activity, scan duration and patient's body mass index in the optimization of FDG imaging protocols on a TOF-PET/CT scanner

Background

Time-of-flight (TOF) PET technology determines a reduction in the noise and improves the reconstructed image quality in low count acquisitions, such as in overweight patients, allowing a reduction of administered activity and/or imaging time. However, international guidelines and recommendations on the ¹⁸F-fluoro-2-deoxyglucose (FDG) activity administration scheme are old or only partially account for TOF technology and advanced reconstruction modalities.

The aim of this study was to optimize FDG whole-body studies on a TOF-PET/CT scanner by using a multivariate approach to quantify how physical figures of merit related to image quality change with acquisition/reconstruction/patient-dependent parameters in a phantom experiment.

Methods

The NEMA-IQ phantom was used to evaluate contrast recovery coefficient (CRC), background variability (BV) and contrast-to-noise ratio (CNR) as a function of changing emission scan duration (ESD), activity concentration (AC), target internal diameter (ID), target-background activity ratio (TBR) and body mass index (BMI). The phantom was filled with an average concentration of 5.3 kBq/ml of FDG solution and the spheres with TBR of 21.2, 8.8 and 5.0 in 3 different sessions. Images were acquired at varying background activity concentration from 5.1 to 1.3 kBq/ml, and images were reconstructed for ESD of 30–151 s per bed position with and without point spread function (PSF) correction. The parameters were all considered in a single analysis using multiple linear regression methods.

Results

As expected, CRC depended only on sphere ID and on PSF application, while BV depended on sphere ID, ESD, AC and BMI of the phantom, in order of decreasing relevance. Noteworthy, ESD and AC resulted as the most significant predictors of CNR variability with a similar relevance, followed by the BMI of the patient and TBR of the lesion.

Conclusions

AC and ESD proved to be effective tools in modulating CNR. ESD could be increased rather than AC to improve image quality in overweight/obese patients to fulfil ALARA principles.

Ultra-low dose whole-body CT for attenuation correction in a dual tracer PET/CT protocol for multiple myeloma

PURPOSE

To investigate within phantoms the minimum CT dose allowed for accurate attenuation correction of PET data and to quantify the effective dose reduction when a CT for this purpose is incorporated in the clinical setting.

METHODS

The NEMA image quality phantom was scanned within a large parallelepiped container. Twenty-one different CT images were acquired to correct attenuation of PET raw data. Radiation dose and image quality were evaluated. Thirty-one patients with proven multiple myeloma who underwent a dual tracer PET/CT scan were retrospectively reviewed. ¹⁸F-fluorodeoxyglucose PET/CT included a diagnostic whole-body low dose CT (WBLDCT: 120 kV-80mAs) and ¹¹C-Methionine PET/CT included a whole-body ultra-low dose CT (WBULDCT) for attenuation correction (100 kV-40mAs). Effective dose and image quality were analysed.

RESULTS

Only the two lowest radiation dose conditions (80 kV-20mAs and 80 kV-10mAs) produced artifacts in CT images that degraded corrected PET images. For all the other conditions (CTDI_vol ≥ 0.43 mGy), PET contrast recovery coefficients varied less than ± 1.2%. Patients received a median dose of 6.4 mSv from diagnostic CT and 2.1 mSv from the attenuation correction CT. Despite the worse image quality of this CT, 94.8% of bone lesions were identifiable.

CONCLUSION

Phantom experiments showed that an ultra-low dose CT can be implemented in PET/CT procedures without any noticeable degradation in the attenuation corrected PET scan. The replacement of the standard CT for this ultra-low dose CT in clinical PET/CT scans involves a significant radiation dose reduction.

Reconstruction of positron emission tomography images using adaptive sliced remeshing strategy

Purpose: The reconstruction of positron emission tomography images is a computationally intensive task which benefits from the use of increasingly complex physical models. Aiming to reduce the computational burden by means of a reduced system matrix, we present a list mode reconstruction approach based on maximum likelihood-expectation maximization and a sliced mesh support. Approach: The reconstruction strategy uses a fully 3D projection along series of 2D meshes arranged in the axial plane of the scanner. These series of meshes describe the continuous volumetric activity using a piece-wise linear function interpolated from the mesh elements. The mesh support is automatically adapted to the underlying structure of the activity by means of a remeshing process. This process finds a high-quality compact mesh representation constrained to a controlled interpolation error. Results: The method is tested using a Monte Carlo simulation of a Hoffman brain phantom and a National Electrical Manufacturers Association image quality phantom acquisition, using different sets of statistics. The reconstructions are compared against a voxelized reconstruction under different conditions, achieving similar or superior results. The number of parameters needed to reconstruct the image in voxel and mesh support is also compared, and the mesh reconstruction permits to reduce the number of nodes used to represent a complex image. Conclusions: The proposed reconstruction strategy reduces the number of parameters needed to describe the activity distribution by more than one order of magnitude for similar voxel size and with similar accuracy than state-of-the-art methods.

CT protocol optimisation in PET/CT: a systematic review

Purpose

Currently, no consistent guidelines for CT scans used within PET/CT examinations are available. This systematic review provides an up-to-date overview of studies to answer the following questions: What are the specific CT protocols used in PET/CT? What are the possible purposes of requiring a CT study within a PET/CT scan? Is the CT protocol obtained from a dosimetric optimisation study?

Materials and method

PubMed/MEDLINE, Cochrane Library, Embase and Scopus were systematically searched for relevant studies in accordance with the PRISMA statement. The literature search was conducted from January 2007 until June 2019. Data derived from studies were standardized in order to reduce possible biases, and they were divided into clinically homogeneous subgroups (adult, child or phantom). Subsequently, we divided the CT protocol intents into 3 types (anatomic localization only, attenuation correction only and diagnostic purpose). A narrative approach was used to summarise datasets and to investigate their heterogeneity (due to medical prescription methodology) and their combination in multiseries CT protocols. When weighted computed tomography dose index (CTDI_w) was available, we calculated the volumetric computed tomography dose index (CTDI_vol) using the pitch value to make the results uniform. Eventually, the correlation between protocol intents and CTDI_vol values was obtained using a Kruskal–Wallis one-way ANOVA statistical test.

Result

Starting from a total of 1440 retrieved records, twenty-four studies were eligible for inclusion in addition to two large multicentric works that we used to compare the results. We analyzed 87 CT protocols. There was a considerable range of variation in the acquisition parameters: tube current–time product revealed to have the most variable range, which was 10–300 mAs for adults and 10–80 mAs for paediatric patients. Seventy percent of datasets presented scans acquired with tube current modulation, 9% used fixed tube current and in 21% of them, this information was not available. Dependence between mean CTDI_vol values and protocol intent was statistically significant (p = 0.002). As expected, in diagnostic protocols, there was a statistically significant difference between CTDI_vol values of with and without contrast acquisitions (11.68 mGy vs 7.99 mGy, p = 0.009). In 13 out of 87 studies, the optimisation aim was not reported; in 2 papers, a clinical protocol was used; and in 11 works, a dose optimisation protocol was applied.

Conclusions

According to this review, the dose optimisation in PET/CT exams depends heavily on the correct implementation of the CT protocol. In addition to this, considering the latest technology advances (i.e. iterative algorithms development), we suggest a periodic quality control audit to stay updated on new clinical utility modalities and to achieve a shared standardisation of clinical protocols. In conclusion, this study pointed out the necessity to better identify the specific CT protocol use within PET/CT scans, taking into account the continuous development of new technologies.

Imaging Metabolically Active Fat: A Literature Review and Mechanistic Insights

Currently, obesity is one of the leading causes death in the world. Shortly before 2000, researchers began describing metabolically active adipose tissue on cancer-surveillance ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in adult humans. This tissue generates heat through mitochondrial uncoupling and functions similar to classical brown and beige adipose tissue in mice. Despite extensive research, human brown/beige fat's role in resistance to obesity in humans has not yet been fully delineated. FDG uptake is the de facto gold standard imaging technique when studying brown adipose tissue, although it has not been rigorously compared to other techniques. We, therefore, present a concise review of established and emerging methods to image brown adipose tissue activity in humans. Reviewed modalities include anatomic imaging with CT and magnetic resonance imaging (MRI); molecular imaging with FDG, fatty acids, and acetate; and emerging techniques. FDG-PET/CT is the most commonly used modality because of its widespread use in cancer imaging, but there are mechanistic reasons to believe other radiotracers may be more sensitive and accurate at detecting brown adipose tissue activity. Radiation-free modalities may help the longitudinal study of brown adipose tissue activity in the future.

Radiation dosimetry considerations for skeletal survey imaging of multiple myeloma

PURPOSE

This paper aims to review the dosimetry and utility of currently implemented imaging modalities for assessment of multiple myeloma and consider the role of tin filtration computed tomography (CT) as a potential replacement to current standard practice.

METHODS

Radiation output of tin CT was measured experimentally and used for software-based dose calculation. Resultant effective dose was then compared to calculated planar radiography doses and published doses of other imaging modalities.

RESULTS

Based on example patient parameters used for modalities and 14 projection planar radiography site protocols, doses are comparable between planar radiography and tin filtration CT (approximately 0.9 and 1.0 mSv respectively). Both studies carried a reduced radiation burden compared to Expected Pathologically Increased Contrast-CT (EPIC-CT), FDG-PET and MIBI SPECT/CT (5.7, 11.1-20.0 and 13.0 mSv respectively).

CONCLUSION

Tin filtered CT provided visualisation of multiple myeloma at doses comparable to planar radiography and where available may be a suitable alternative, following due consideration of patient specific justification and optimisation in line with best practice.

Body Weight-Based Protocols During Whole Body FDG PET/CT Significantly Reduces Radiation Dose without Compromising Image Quality:Findings in a Large Cohort Study

RATIONALE AND OBJECTIVES

To investigate radiation dose reduction during whole body fluorodeoxyglucose (¹⁸F-FDG) positron emission tomographic (PET)/computed tomography (CT) by employing weight-based protocols.

MATERIALS AND METHODS

One thousand and twenty-eight patients were referred for ¹⁸F-FDG PET/CT study with one of two protocols: conventional protocol I; 120 kVp, 120 mAs, 0.5 second rotation time, pitch 0.8 mm/rot across all body weights; four-tier body weight protocol II all used 140 kVp, 0.75 seconds rotation time and pitch 0.8 mm/rot: Protocol A (≤60 kg): 35 mAs, Protocol B (61-80 kg): 50 mAs, Protocol C (81-100 kg): 65 mAs, and Protocol D: (>101 kg): 100 mAs. All protocols employed tube current modulation. Quantitative and qualitative image visual grading characteristics assessed image quality.

RESULTS

Patient demographics demonstrated no significant difference between each protocol except for patient weight in weight protocol IIB (p < 0.009). Mean effective dose in all protocols were significantly lower in Protocol B compared to A (p < 0.009). Contrast-to-noise ratio demonstrated no differences between each protocol (p < 0.21) except for weight protocol in protocol IIA (<60 kg, p = 0.035) with the visual grading characteristics demonstrating preference over protocol II compared to I.

CONCLUSION

Significant reduction in radiation dose can be achieved using patient-specific body weight-based protocols during whole-body ¹⁸F-FDG PET/CT without compromising image quality when employing weight-based protocols.

Quantification of DNA damage in patients undergoing non-contrast and contrast enhanced whole body PET/CT investigations using comet assay and micronucleus assay

Objective: To quantify DNA damage in patients undergoing non-contrast and contrast-enhanced ¹⁸F-FDG PET/CT whole body positron emission tomography/computed tomography (WB PET/CT) investigations using comet assay technique and micronucleus assay, and to study the effect of other baseline parameters of patients on DNA damage. Methodology: Eighty-four patients referred for ¹⁸F-FDG PET/CT investigation were included in the study of which 44 patients underwent contrast-enhanced WB PET/CT and 40 patients underwent non-contrast WB PET/CT investigations. The investigations were performed on Discovery 690 PET/CT. For contrast-enhanced investigation, Omnipaque300 was injected intravenously based on the patient body weight. Absorbed dose resulting from the intravenous administration of ¹⁸F-FDG was estimated using the ICRP 106 dose coefficients. Radiation dose from the acquisition of CT scans was estimated using CT dose index and dose-length product. Blood samples were collected from the patients for DNA damage analysis. Comet assay and MN assay was used to assess the DNA damage. The Differences in the comet TM (Tail Moment) and MNBC % in both groups were calculated. Result: The radiation dose received by the study population during ¹⁸F-FDG WB PET/CT examination was 27.03 ± 2.33 mSv. Comet TM and percentage frequency of MNBC % was 65.22 ± 35.42 and 18.55 ± 10.14, respectively in the patients injected with contrast and 42.49 ± 28.52 and 13.76 ± 7.52 for non-contrast group. Significant increase in DNA damage was observed in the contrast group as compared to non-contrast group. Significant association was observed between patient weight, contrast volume and TM and MNBC%. Baseline parameters of the patients did not show significant correlation with TM and MNBC%. Conclusion: The patients undergoing contrast-enhanced WB PET/CT investigations have demonstrated higher DNA damage. The DNA damage was also observed to be more in heavier patients. The other baseline parameters of patients like age, sex, CBG, serum creatinine did not show any correlation with DNA damage.

The effects of image reconstruction algorithms on topographic characteristics, diagnostic performance and clinical correlation of metabolic brain networks in Parkinson's disease

PURPOSE

The purpose of this study was to evaluate the effects of different image reconstruction algorithms on topographic characteristics and diagnostic performance of the Parkinson's disease related pattern (PDRP).

METHODS

FDG-PET brain scans of 20 Parkinson's disease (PD) patients and 20 normal controls (NC) were reconstructed with six different algorithms in order to derive six versions of PDRP. Additional scans of 20 PD, 25 atypical parkinsonism (AP) patients and 20 NC subjects were used for validation. PDRP versions were compared by assessing differences in topographies, individual subject scores and correlations with patient's clinical ratings. Discrimination of PD from NC and AP subjects was evaluated across cohorts.

RESULTS

The region weights of the six PDRPs highly correlated (R ≥ 0.991; p < 0.0001). All PDRPs' expressions were significantly elevated in PD relative to NC and AP subjects (p < 0.0001) and correlated with clinical ratings (R ≥ 0.47; p < 0.05). Subject scores of the six PDRPs highly correlated within each of individual healthy and parkinsonian groups (R ≥ 0.972, p < 0.0001) and were consistent across the algorithms when using the same reconstruction methods in PDRP derivation and validation. However, when derivation and validation reconstruction algorithms differed, subject scores were notably lower compared to the reference PDRP, in all subject groups.

CONCLUSION

PDRP proves to be highly reproducible across FDG-PET image reconstruction algorithms in topography, ability to differentiate PD from NC and AP subjects and clinical correlation. When calculating PDRP scores in scans that have different reconstruction algorithms and imaging systems from those used for PDRP derivation, a calibration with NC subjects is advisable.