Hybrid imaging worldwide-challenges and opportunities for the developing world: a report of a Technical Meeting organized by IAEA

Accurate lateralization and classification of MRI-negative 18F-FDG-PET-positive temporal lobe epilepsy using double inversion recovery and machine-learning

OBJECTIVE

The main objective of this study was to determine the ability of double inversion recovery (DIR) data coupled with machine-learning algorithms to distinguish normal individuals from epileptic subjects and to identify the laterality of the focus side in MRI-negative, PET-positive temporal lobe epilepsy (TLE) patients.

MATERIALS AND METHODS

We used whole-brain DIR data as the input features with which to train a linear support-vector machine model in 63 participants who underwent high-resolution structural MRI and DIR scans. The subjects included 20 left TLE patients, 19 right TLE patients, and 24 healthy controls (HCs).

RESULTS

Using the DIR data, we achieved a robust accuracy of 87.30% for discriminating among the left TLE, right TLE, and HC groups as well as 84.61%, 97.72%, and 93.02% prediction accuracies for distinguishing left TLE from right TLE, HC from right TLE, and HC from left TLE, respectively.

INTERPRETATION

Our experimental results suggest that DIR data coupled with machine-learning algorithms provide a promising approach to identifying MRI-negative TLE patients, especially when fluorodeoxyglucose-PET is not available.

HIDA and Seek: Challenges of Scintigraphy to Diagnose Bile Reflux Post-Bariatric Surgery

INTRODUCTION

Oesophageal bile reflux after bariatric surgery may trigger development of Barrett's oesophagus. Gastro-oesophageal reflux of bile is captured by hepatobiliary iminodiacetic acid (HIDA) scintigraphy; however, anatomical and physiological changes after bariatric surgery warrant protocol modifications to optimise bile reflux detection.

METHODS

HIDA scintigraphy occurred 6 months after either sleeve gastrectomy, Roux-en-Y gastric bypass or one-anastomosis gastric bypass. Standard HIDA scanning involves (i) 6-h fast and 24-h abstinence from opioids; (ii) IV administration of 99mTc di-isopropyl iminodiacetic acid; and (iii) dual anterior/posterior 60-min dynamic scanning of the duodenum, stomach and oesophagus. Three challenges were identified, and modifications were implemented, namely, (1) anatomical localisation of refluxed bile on planar scintigraphy was improved by adding a SPECT/CT for 3D imaging; (2) impaired cholecystokinin-controlled gallbladder emptying, following bypassed duodenum, was addressed by ingestion of a 'fatty meal'; and (3) intestinal hypomotility after gastric bypass was counteracted by longer scan duration (75-90 min) to allow bile to pass beyond the gastro-jejunal anastomosis.

RESULTS

HIDA scan was undertaken in 18 patients, 13 of whom underwent the modified protocol. The tailored protocol ameliorated issues identified with the standard HIDA scan protocol; thus, accurate anatomical localisation was achieved in all patients, no delayed gallbladder emptying was observed, and bile was observed beyond the gastro-jejunal anastomosis in all gastric bypass patients. The modified technique was well tolerated by patients.

CONCLUSION

A tailored HIDA scan protocol with addition of a SPECT-CT scan, ingestion of a fatty meal and prolonged scanning duration results in enhanced bile reflux detection in post-bariatric surgical patients.

Medical imaging and nuclear medicine: a Lancet Oncology Commission

The diagnosis and treatment of patients with cancer requires access to imaging to ensure accurate management decisions and optimal outcomes. Our global assessment of imaging and nuclear medicine resources identified substantial shortages in equipment and workforce, particularly in low-income and middle-income countries (LMICs). A microsimulation model of 11 cancers showed that the scale-up of imaging would avert 3·2% (2·46 million) of all 76·0 million deaths caused by the modelled cancers worldwide between 2020 and 2030, saving 54·92 million life-years. A comprehensive scale-up of imaging, treatment, and care quality would avert 9·55 million (12·5%) of all cancer deaths caused by the modelled cancers worldwide, saving 232·30 million life-years. Scale-up of imaging would cost US$6·84 billion in 2020-30 but yield lifetime productivity gains of $1·23 trillion worldwide, a net return of $179·19 per $1 invested. Combining the scale-up of imaging, treatment, and quality of care would provide a net benefit of $2·66 trillion and a net return of $12·43 per $1 invested. With the use of a conservative approach regarding human capital, the scale-up of imaging alone would provide a net benefit of $209·46 billion and net return of $31·61 per $1 invested. With comprehensive scale-up, the worldwide net benefit using the human capital approach is $340·42 billion and the return per dollar invested is $2·46. These improved health and economic outcomes hold true across all geographical regions. We propose actions and investments that would enhance access to imaging equipment, workforce capacity, digital technology, radiopharmaceuticals, and research and training programmes in LMICs, to produce massive health and economic benefits and reduce the burden of cancer globally.

Arterial Spin Labeling is a Useful MRI Method for Presurgical Evaluation in MRI-Negative Focal Epilepsy

Arterial spin labeling (ASL) is an MRI technique measuring brain perfusion using magnetically labeled blood as a tracer. The clinical utility of ASL for presurgical evaluation in non-lesional epilepsy as compared with the quantitative analysis of interictal [¹⁸F] fluorodeoxyglucose PET (FDG-PET) was studied. In 10 patients (4 female; median age 29 years) who underwent a complete presurgical evaluation followed by surgical resection, the presurgical FDG-PET and ASL scans were compared with the resection masks using asymmetry index (AI) maps. The positive predictive value (PPV) and sensitivity (SEN), were calculated from the number of voxels inside the mask (true positive), and outside the mask (false positive). The comparison of the PPVs showed better PPV in 6 patients using ASL and in 2 patients with PET. SEN was better in 4 patients using ASL and in 5 patients with PET. According to the Wilcoxon signed rank test for PPV (p = 0.74) and for SEN (p = 0.43), these methods have similar predictive power. ASL is a useful method for presurgical evaluation in non-lesional epilepsy. The main benefits of ASL over PET are that it avoids radiation exposure for patients, and it offers lower costs, higher availability, and better time efficiency.

Gallium citrate-67 single-photon emission computed tomography/computed tomography for localizing the foci of classic fever and inflammation of unknown origin: A retrospective study of diagnostic yield

OBJECTIVES

Only few studies have assessed the use of gallium citrate-67 single-photon emission computed tomography/computed tomography (67Ga-SPECT/CT) for localizing the foci of classic fever of unknown origin (FUO) and inflammation of unknown origin (IUO). Hence, the current study aimed to assess the diagnostic contribution of 67Ga-SPECT/CT in a tertiary referral setting where nuclear imaging tests are performed after an unsuccessful comprehensive primary diagnostic workup.

METHODS

We retrospectively assessed the medical records of 27 adult patients with FUO/IUO who had an unsuccessful diagnostic workup and who underwent 67Ga-SPECT/CT for the localization of FUO/IUO foci in our university hospital between 2013 and 2019. The primary outcome was diagnostic yield. The secondary outcomes were overall clinical efficacy and spontaneous remission of FUO/IUO symptoms in patients with a negative 67Ga-SPECT/CT finding.

RESULTS

Almost all patients completed the recommended diagnostic workup, except for urine culture and abdominal ultrasonography. Moreover, prior to 67Ga-SPECT/CT, all patients underwent thoraco-abdominopelvic CT scan, which was a non-diagnostic procedure. After a median follow-up of 843 days, the cause was identified in 16 (59%) patients. 67Ga-SPECT/CT successfully localized the FUO/IUO foci in eight patients (diagnostic yield = 30%; 95% confidence interval [CI]: 14%-50%). However, the causes remained unknown during follow-up in 11 (41%) patients. Among them, five experienced spontaneous regression of symptoms. 67Ga-SPECT/CT was negative in four of the five patients with spontaneous regression in symptoms without a definite cause. Considering this an important event, the overall clinical efficacy of 67Ga-SPECT/CT increased to 44% (95% CI: 25%-65%).

CONCLUSION

67Ga-SPECT/CT had an acceptable diagnostic yield for the localization of FUO/IUO foci, which are challenging to diagnose, in a contemporary tertiary referral care setting. In patients who experienced spontaneous regression in symptoms with an unexplained cause, the absence of abnormal uptake might indicate prospective spontaneous remission. Thus, 67Ga-SPECT/CT could be an active first-line nuclear imaging modality in settings where fluorine-18-fluorodeoxy glucose positron emission tomography and computed tomography is not available for the assessment of FUO/IUO causes.

FLAIR-Wise Machine-Learning Classification and Lateralization of MRI-Negative 18F-FDG PET-Positive Temporal Lobe Epilepsy

Objective: In this study, we investigated the ability of fluid-attenuated inversion recovery (FLAIR) data coupled with machine-leaning algorithms to differentiate normal and epileptic brains and identify the laterality of focus side in temporal lobe epilepsy (TLE) patients with visually negative MRI.

Materials and Methods: The MRI data were acquired on a 3-T MR system (Philips Medical Systems). After pre-proceeding stage, the FLAIR signal intensities were extracted from specific regions of interest, such as the amygdala, cerebral white matter, inferior temporal gyrus, middle temporal gyrus, parahippocampal gyrus, superior temporal gyrus, and temporal pole, and fed into a classification framework followed by a support vector machine as classifier. The proposed lateralization framework was assessed in a group of MRI-negative unilateral TLE patients (N = 42; 23 left TLE and 19 right TLE) and 34 healthy controls (HCs) based on a leave-one-out cross-validation strategy.

Results: Using the FLAIR data, we obtained a 75% accuracy for discriminating the three groups, as well as 87.71, 83.01, and 76.19% accuracies for HC/right TLE, HC/left TLE, and left TLE/right TLE tasks, respectively.

Interpretation: The experimental results show that FLAIR data can potentially be considered an informative biomarker for improving the pre-surgical diagnostic confidence in patients with MRI-negative TLE.

Two decades of SPECT/CT - the coming of age of a technology: An updated review of literature evidence

PURPOSE

Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) was introduced as a hybrid SPECT/CT imaging modality two decades ago. The main advantage of SPECT/CT is the increased specificity achieved through a more precise localization and characterization of functional findings. The improved diagnostic accuracy is also associated with greater diagnostic confidence and better inter-specialty communication.

METHODS

This review presents a critical assessment of the relevant literature published so far on the role of SPECT/CT in a variety of clinical conditions. It also includes an update on the established evidence demonstrating both the advantages and limitations of this modality.

CONCLUSIONS

For the majority of applications, SPECT/CT should be a routine imaging technique, fully integrated into the clinical decision-making process, including oncology, endocrinology, orthopaedics, paediatrics, and cardiology. Large-scale prospective studies are lacking, however, on the use of SPECT/CT in certain clinical domains such as neurology and lung disorders. The review also presents data on the complementary role of SPECT/CT with other imaging modalities and a comparative analysis, where available.

Similar and Differing Distributions Between 18F-FDG-PET and Arterial Spin Labeling Imaging in Temporal Lobe Epilepsy

Background: Despite the increasing use of arterial spin labeling (ASL) in patients with epilepsy, little is known about its brain regional distribution pattern, including diaschisis, and its correspondence with FDG-PET. Here, we investigated the regional match and mismatch between FDG-PET and ASL in temporal lobe epilepsy (TLE). Methods: We recruited 27 patients with unilateral TLE, who underwent inter-ictal ASL and FDG-PET scans. These images were spatially normalized using Statistical Parametric Mapping 12, and the regional values in both ASL and FDG-PET were calculated using PMOD software within 20 volumes of interest (VOIs), including the temporal lobe, adjacent cortices, subcortical structures, and cerebellum. ASL images of 37 healthy controls were also analyzed and compared. Results: Whereas, ASL showed significant side differences, mainly in the temporal and frontal lobes, the significant abnormalities in FDG-PET were more widespread and included the insula and supramarginal gyrus. Ipsilateral thalamic reduction was found in FDG-PET only. The detectability of the focus side compared with the contralateral side was generally higher in FDG-PET. The discriminative values in ASL compared with healthy controls were higher in temporal neocortex and amygdala VOIs. Conclusions: There are similar and differing regional distributions between FDG-PET and ASL in TLE, possibly reflecting regional match and mismatch of cerebral blood flow and metabolism. At this stage, it seems that ASL couldn't present comparable clinical usefulness with FDG-PET. These findings deepen our knowledge of ASL imaging and are potentially useful for its further application.

Ensuring effective and sustainable radionuclide delivery and its impact on the development of nuclear medicine in the developing world with special reference to Nigeria

Recent activities of Boko Haram, a local extremist group in Nigeria, raise concerns about a nuclear terrorist attack. Whereas nuclear medicine (NM) relies on the timely delivery of radioactive sources, a robust security structure that assures public safety is the backbone for its beneficial use. NM radionuclides have short half-lives and carry an insignificant risk for acts of terrorism. Yet, their importation and delivery in Nigeria receive undue scrutiny in a bid to implement a strict nuclear security regime. These actions prevent timely delivery of radionuclides with direct consequences on quality and economic viability of nuclear medicine. There have been no accounts of terrorist acts accomplished with NM radionuclides. Thus, it is important the NM community question the current approach that has contributed to the loss of NM services in Nigeria and proposes a more logical strategy for securing their supply. We also highlight the need for developing local pragmatic solutions when implementing global recommendations in developing countries.

Abnormal neurite density and orientation dispersion in unilateral temporal lobe epilepsy detected by advanced diffusion imaging

Background

Despite recent advances in diffusion MRI (dMRI), there is still limited information on neurite orientation dispersion and density imaging (NODDI) in temporal lobe epilepsy (TLE). This study aimed to demonstrate neurite density and dispersion in TLE with and without hippocampal sclerosis (HS) using whole-brain voxel-wise analyses.

Material and methods

We recruited 33 patients with unilateral TLE (16 left, 17 right), including 14 patients with HS (TLE-HS) and 19 MRI-negative ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET)-positive patients (MRI-/PET+ TLE). The NODDI toolbox calculated the intracellular volume fraction (ICVF) and orientation dispersion index (ODI). Conventional dMRI metrics, that is, fractional anisotropy (FA) and mean diffusivity (MD), were also estimated. After spatial normalization, all dMRI parameters (ICVF, ODI, FA, and MD) of the patients were compared with those of age- and sex-matched healthy controls using Statistical Parametric Mapping 12 (SPM12). As a complementary analysis, we added an atlas-based region of interest (ROI) analysis of relevant white matter tracts using tract-based spatial statistics.

Results

We found decreased neurite density mainly in the ipsilateral temporal areas of both right and left TLE, with the right TLE showing more severe and widespread abnormalities. In addition, etiology-specific analyses revealed a localized reduction in ICVF (i.e., neurite density) in the ipsilateral temporal pole in MRI-/PET+ TLE, whereas TLE-HS presented greater abnormalities, including FA and MD, in addition to a localized hippocampal reduction in ODI. The results of the atlas-based ROI analysis were consistent with the results of the SPM12 analysis.

Conclusion

NODDI may provide clinically relevant information as well as novel insights into the field of TLE. Particularly, in MRI-/PET+ TLE, neurite density imaging may have higher sensitivity than other dMRI parameters. The results may also contribute to better understanding of the pathophysiology of TLE with HS.

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We examined temporal lobe epilepsy (TLE) with or without hippocampal sclerosis (HS).

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Neurite orientation dispersion and density imaging (NODDI) was used.

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Ipsilateral reduction of neurite density was found in MRI-negative PET-positive TLE.

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More extensive abnormalities were presented in TLE with HS.

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NODDI may provide clinical relevance and novel insights into the field of TLE.

Current Practices in Myocardial Perfusion Scintigraphy in Brazil and Adherence to the IAEA Recommendations: Results of a Cross-Sectional Study

BACKGROUND

Data on the current situation of nuclear medicine practices in cardiology in Brazil are scarce. The International Atomic Energy Agency (IAEA) has recommended eight "good practices" to minimize patients' ionizing radiation exposure during myocardial perfusion scintigraphy (MPS).

OBJECTIVES

To assess the adoption of the eight good practices in MPS in Brazil.

METHODS

Cross-sectional study with data obtained by use of a questionnaire. All hypothesis tests performed considered a significance level of 5%.

RESULTS

We observed that 100% of the nuclear medicine services (NMS) assessed do not use thallium-201 as the preferred protocol. Regarding the use of technetium-99m, 57% of the NMS administer activities above the threshold recommended by the IAEA (36 mCi) or achieve an effective dose greater than 15 millisievert (mSv). The abbreviated stress-only myocardial perfusion imaging is not employed by 94% of the NMS; thus, only 19% count on strategies to reduce the radioactive doses. Approximately 52% of the NMS reported always performing dose adjustment for patient's weight, while 35% administer poorly calculated doses in the one-day protocol.

CONCLUSION

A considerable number of NMS in Brazil have not adopted at least six practices recommended by the IAEA. Despite the difficulties found in nuclear practice in some Brazilian regions, almost all obstacles observed can be overcome with no cost increase, emphasizing the importance of developing strategies for adopting "good practices" when performing MPS.

Current status of nuclear cardiology practice in Latin America and the Caribbean

The burden of cardiovascular diseases (CVDs) in the world is ever growing. They represent the first cause of death worldwide and in Latin America. Nuclear cardiology has a well-established role in the management of patient with CVDs and is being increasingly integrated into the healthcare systems in the region. However, there remains variability as to the infrastructure available across the countries, in terms of existing technology, radiopharmaceuticals, and human resources. The approximate number of gamma (γ) cameras in the region is 1348, with an average of 2.25 per million population; Argentina and Brazil having the largest number. Nearly 80% of the existing cameras are single-photon emission tomography (SPECT), of which 8% are hybrid SPECT-CT systems. Positron emission tomography technology is steadily increasing, and currently, there is an average of 0.25 scanners per million inhabitants, indicating that there is a potential to expand the capacities in order to cover the needs. Four countries have nuclear reactors for research purposes, which allow the production of technetium-99 m (Argentina, Chile, Mexico and Peru), while four (Argentina, Brazil, Cuba, and Mexico) assemble 99Mo-99mTc generators. As for the nuclear cardiology studies, about 80% of studies performed are gated SPECT myocardial perfusion imaging; less than 10% are multi-gated acquisition (mainly for evaluation of cardiac toxicity in cancer patients), and the other 10% correspond to other types of studies, such as viability detection, and adrenergic innervation studies with 123I-MIBG. Physical stress is preferred, when possible, based on the clinical condition of the patient. Regarding human resources, there is an average of 1.1 physicians and 1.3 technologists per γ camera, with 0.1 medical physicists and 0.1 radiopharmacists per center in the region. The future of nuclear cardiology in Latin America and the Caribbean is encouraging, with great potential and possibilities for growth. National, regional, and international cooperation including support from scientific societies and organizations such as International Atomic Energy Agency, American Society of Nuclear Cardiology, and Latin American Association of Biology and Nuclear Medicine Societies, as well as governmental commitment are key factors for the development of the specialty. A multimodality approach in cardiac imaging will contribute to a better management of patients with CVDs.

Current Status of Nuclear Medicine Practice in Latin America and the Caribbean

The practice of nuclear medicine (NM) in the Latin American and Caribbean region has experienced important growth in the last decade. However, there is great heterogeneity among countries regarding the availability of technology and human resources. According to data collected through June 2014 by the International Atomic Energy Agency (IAEA), the total number of γ cameras in the region is 1,231, with an average of 2.16 per million inhabitants. Over 90% of the equipment is SPECT cameras; 7.6% of which have hybrid technology. There are 161 operating PET or PET/CT cameras in 12 member states, representing a rate of 0.3 per million people. Most NM centers belong to the private health system and are in capitals or major cities. Only 4 countries have the capability of assembling 99Mo-99mTc generators, and 2 countries produce 99mTc from nuclear reactors. Cold kits are produced in some countries, and therapeutic agents are mostly imported from outside the region. There are 35 operative cyclotrons. In relation to human resources: there is 1 physician per γ camera, 1.6 technologists per γ camera, 0.1 medical physicist per center, and approximately 0.1 radiochemist or radiopharmacist per center. Nearly 94% of the procedures are diagnostic. PET studies represent about 4% of the total. The future of NM in the Latin American and Caribbean region is promising, with great potential and possibilities. Some of the most important factors driving the region toward greater homogeneity in the availability and application of NM, and bridging the gaps between countries, are clinician awareness of the importance of NM in managing diseases prevalent in the region, increased building of capacity, continuous and strong support from international organizations such as the IAEA through national and regional projects, and strong public-private partnerships and government commitment.

Technological advances in hybrid imaging and impact on dose

New imaging technologies utilising X-rays and radiopharmaceuticals have developed rapidly. Clinical application of computed tomography (CT) has revolutionised medical imaging and plays an enormous role in medical care. Due to technical improvements, spatial, contrast and temporal resolutions have continuously improved. In spite of significant reduction of CT doses during recent years, CT is still a dominating source of radiation exposure to the population. Combinations with single photon emission computed tomography (SPECT) and positron emission tomography (PET) and especially the use of SPECT/CT and PET/CT, provide important additional information about physiology as well as cellular and molecular events. However, significant dose contributions from SPECT and PET occur, making PET/CT and SPECT/CT truly high dose procedures. More research should be done to find optimal activities of radiopharmaceuticals for various patient groups and investigations. The implementation of simple protocol adjustments, including individually based administration, encouraged hydration, forced diuresis and use of optimised voiding intervals, laxatives, etc., can reduce the radiation exposure to the patients. New data about staff doses to fingers, hands and eye lenses indicate that finger doses could be a problem, but not doses to the eye lenses and to the whole body.

The added value of hybrid ventilation/perfusion SPECT/CT in patients with stable COPD or apparently healthy smokers. Cancer-suspected CT findings in the lungs are common when hybrid imaging is used

Ventilation/perfusion (V/P) single-photon emission computed tomography (SPECT) is recognized as a diagnostic method with potential beyond the diagnosis of pulmonary embolism. V/P SPECT identifies functional impairment in diseases such as heart failure (HF), pneumonia, and chronic obstructive pulmonary disease (COPD). The development of hybrid SPECT/computed tomography (CT) systems, combining functional with morphological imaging through the addition of low-dose CT (LDCT), may be useful in COPD, as these patients are prone to lung cancer and other comorbidities. The aim of this study was to investigate the added value of LDCT among healthy smokers and patients with stable COPD, when examined with V/P SPECT/CT hybrid imaging. Sixty-nine subjects, 55 with COPD (GOLD I-IV) and 14 apparently healthy smokers, were examined with V/P SPECT and LDCT hybrid imaging. Spirometry was used to verify COPD grade. Only one apparently healthy smoker and three COPD patients had a normal or nearly normal V/P SPECT. All other patients showed various degrees of airway obstruction, even when spirometry was normal. The same interpretation was reached on both modalities in 39% of the patients. LDCT made V/P SPECT interpretation more certain in 9% of the patients and, in 52%, LDCT provided additional diagnoses. LDCT better characterized the type of emphysema in 12 patients. In 19 cases, tumor-suspected changes were reported. Three of these 19 patients (ie, 4.3% of all subjects) were in the end confirmed to have lung cancer. The majority of LDCT findings were not regarded as clinically significant. V/P SPECT identified perfusion patterns consistent with decompensated left ventricular HF in 14 COPD patients. In 16 patients (23%), perfusion defects were observed. HF and perfusion defects were not recognized with LDCT. In COPD patients and long-time smokers, hybrid imaging had added value compared to V/P SPECT alone, by identifying patients with lung malignancy and more clearly identifying emphysema. V/P SPECT visualizes comorbidities to COPD not seen with LDCT, such as pulmonary embolism and left ventricular HF.