Technical concepts on blood pool phase SPECT (acquisition, reconstruction).

Guidelines for bone scintigraphy are well established and recommend the use of planar early phase images to investigate a number of clinical indications. With recent advances in gamma camera technology the use of SPECT/CT imaging in the early phases is now possible, offering the potential of improved diagnostic confidence and prognostic value. To date little work has been carried out to optimize the acquisition of early phase bone images using SPECT/CT with most of the available studies acquiring SPECT images after the traditional planar images to allow comparison of the two techniques. Imaging durations of 7 to 10 minutes have been commonly used. However, the use of iterative reconstruction algorithms has been investigated with rapid SPECT imaging to allow imaging durations as low as 4 minutes. The use of CZT based systems with increased sensitivity and improved energy and spatial resolution also offers the potential to reduce imaging times. The optimization of projection measurement order has been investigated as a method of reducing image artefacts as a result of changing tracer distribution during the SPECT acquisition. In this article we consider the current state of early phase SPECT imaging and possible areas for future investigation as well as recommendations for departments looking to adopt blood pool SPECT imaging as part of their routine clinical practice.

[18F]FDG PET/CT in rheumatoid arthritis.

[18F]fluorodeoxyglucose (FDG) PET/CT can be used to image the inflammation in rheumatoid arthritis. Specifically, the synovial metabolic activity can be evaluated visually and measured using standard uptake values. Fluorine-18-labeled Sodium fluoride (NaF) PET/CT can be used to determine synovial osteoblastic activity. Response assessment using FDG PET/CT is routine in many cancers and this is now an emerging technique for rheumatoid arthritis. Vasculitis in rheumatoid arthritis (RA) can be also studied with FDG PET/CT and aortic calcification with NaF PET/CT. These techniques could be useful in determining RA disease severity. FDG PET/CT is a useful technique to exclude underlying malignancy when RA does not follow the expected course. A number of novel tracers are being studied with regard to their applicability in rheumatoid arthritis and some of these could even be used in a theranostic manner in the future.

Update on Imaging of Inflammatory Arthritis and Related Disorders.

Arthritis and other rheumatic disorders are very frequent in the general population and responsible for a huge physical and disability burden to affected patients as well as a major cost to the society. Precise evaluation often relies on clinical data only but additional imaging may be required i) for a more objective assessment of the disease status, such as in rheumatoid arthritis (RA) or ankylosing spondyloarthritis (AS), ii) for providing prognostic information and evaluating response to treatment or iii) for establishing diagnosis, in patients with unclear clinical picture, such as polymyalgia rheumatica (PMR) and large-vessel vasculitis (LVV). Besides radiological techniques (x-rays, ultrasound, and MRI), functional and molecular imaging has emerged as a valid tool for this purpose in several disorders. Bone scanning has long been a method of choice but is now more used as a triage tool in patients with unclear complaints, including degenerative disorders (eg osteoarthritis). 18F-FDG-PET/CT (FDG) proved efficient in assessing the extent of the disease and response to treatment in RA and related disorders, and to provide accurate diagnosis in some systemic disorders, including PMR and LVV. Based on glucose metabolism, FDG-PET/CT is able to show increased metabolism in peripheral cells involved in inflammation (eg neutrophils, lymphocytes or monocytes/macrophages) but also in fibroblasts that proliferate in the pannus. The lack of specificity of FDG is a limitation and many alternative tracers were developed at the preclinical stage or applied in the clinics, especially within clinical trials. They include imaging of macrophages using translocator protein (TSPO), folate-receptors or other targets on activated cells. These new tools will undoubtedly become more and more available in the everyday clinical workup of patients with rheumatisms. Finally, it should be kept in mind that a very simple tracer, 18F-fluoride is widely more performant in AS than FDG.

Prostate cancer bone metastases confined to the distal left lower limb.

Bone metastases from prostate cancer most commonly affect the axial and proximal appendicular skeleton with rare involvement of the distal limbs. We describe a case of multiple bone metastases confined to the left lower limb in a patient with biochemical recurrence of prostate cancer. Following an initial post-operative PSA rise, the patient received a course of salvage radiotherapy to the pelvis, however, the PSA level continued to rise and two consequent staging CT scans were negative for local recurrence and metastatic disease. Subsequent development of left ankle pain and swelling led the patient to present to his General Practitioner, which triggered a series of imaging investigations that revealed isolated left lower limb bone metastases. This case report highlights the need to consider peripheral limb bone metastases in patients with biochemical recurrence of prostate cancer, particularly in the setting of a negative staging CT scan and/or bone pain.

Interobserver Agreement in the Diagnosis of Parkinson Disease with Cardiac 123I-Metaiodobenzylguanidine Scintigraphy.

The aim of this study was to analyze the interobserver agreement of visual and quantitative assessment of cardiac 123I-metaiodobenzylguanidine scintigraphy. Methods: Planar images were acquired using a low-energy collimator. The heart-to-mediastinum (HM) ratio was adjusted for the use of a low-energy collimator, using a published formula. Interpretation was undertaken both visually and after the addition of adjusted HM ratios. Image findings were classified as normal, abnormal, or borderline. Results: The cohort consisted of 10 patients. On visual interpretation only, there was strong agreement on the interpretation of the scan (κ = 0.82, P < 0.01). Adjusted HM ratios led to a significant increase in mean ratios (1.79 vs. 1.36, P = 0.02) and, when utilized in reporting, resulted in perfect agreement (κ = 1.0, P < 0.01). Conclusion: The use of quantified HM ratios adjusted for low-energy collimator use improves on visual assessment alone and allowed for excellent interobserver agreement.

Pleural, pancreatic and prostatic involvement in IgG4-related disease mimicking pancreatic head malignancy.

We describe the case of a gentleman with pleural thickening. On follow-up imaging, dilatation of the main pancreatic and common biliary ducts was noted and an initial diagnosis of pancreatic malignancy was made. During his preoperative workup for pancreatic head malignancy, a PET-CT was performed, which demonstrated increased uptake in the pancreas, in the pleura and in the prostate gland. This raised the possibility of immunoglobulin G4-related disease (IgG4-RD), which was effectively treated with oral steroids. IgG4-RD is a well-described cause of autoimmune pancreatitis but can affect other regions, including the pleura and prostate. It is essential that radiologists are aware of the imaging findings in IgG4-RD and can direct clinicians towards this important multisystem diagnosis.

18FDG-PET/CT findings in COVID-19: a single centre retrospective radiological review.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes the infectious disease COVID-19, was declared a global pandemic in March 2020. As radiology departments recommence 18FDG-PET/CT imaging, it is likely that both asymptomatic and specific symptomatic patients with COVID-19 infection will be imaged, particularly if the disease becomes endemic in the UK. We review the clinical scenarios where 18FDG-PET/CT could be performed in COVID-19 positive patients. Our local protocol for safely scanning known COVID-19 positive patients is described, highlighting considerations for other departments. We present the findings from a series of known COVID-19 positive patients and two further asymptomatic cases evaluated with18FDG-PET/CT. Classic, indeterminate, normal and non-COVID-19 manifestations on both the 18FDG-PETand low dose CT component are described as an aid for radiologists and nuclear medicine physicians when reporting 18FDG PET/CT.

The Effect of an Asymmetric Energy Window on Bone Scintigraphy Image Quality.

Bone scintigraphy is one of the most common nuclear medicine tests. Previous work investigated the effectiveness of an asymmetric window (ASW) for planar bone scintigraphy using simulation and phantom data. Phantom studies concluded that the ASW improved both the resolution and the contrast-to-noise ratio when imaging objects with high scatter. The aim of this study was to confirm this improvement increased image quality in patients. This study also investigated whether the differences between a symmetric window (SW) and an ASW depended on body mass index. Methods: Fifty-eight patients had 2 scans: a standard scan using an SW of 140 keV ± 10% and a scan using an ASW of 140 keV + 10% and - 7.5%. Three readers independently compared the 2 image sets and scored them using a 5-score scale (ranging from 1 = ASW better [clinically important] to 5 = SW better [clinically important]). Scores from all radiologists were pooled and analyzed statistically. A P value of less than 0.05 was considered statistically significant. Results: In 93 cases (53%), the readers scored the ASW images better than the SW images. In 5 cases (3%), the ASW images were preferred, with the difference considered clinically important; there were no cases in which the SW was similarly preferred. For the sign test, we determined whether the total of 93 scores of 1 or 2 (ASW preferred) was significantly different from the 15 scores of 4 or 5 (SW preferred). The P value was less than 0.00001, demonstrating that the difference was significant. Conclusion: In patients undergoing bone scintigraphy, ASW provided an improvement in image quality that in some cases was judged clinically important.

Return of the pulmonary nodule: the radiologist's key role in implementing the 2015 BTS guidelines on the investigation and management of pulmonary nodules.

The British Thoracic Society has published new comprehensive guidelines for the management of pulmonary nodules. These guidelines are significantly different from those previously published, as they use two malignancy prediction calculators to better characterize the risk of malignancy. There are recommendations for a higher nodule size threshold for follow-up (≥5 mm or ≥80 mm(3)) and a reduction of the follow-up period to 1 year for solid pulmonary nodules; both of these will reduce the number of follow-up CT scans. PET-CT plays a crucial role in characterization also, with an ordinal scale being recommended for reporting. Radiologists will be the key in implementing these guidelines, and routine use of volumetric image-analysis software will be required to manage patients with pulmonary nodules correctly.