Future of thoracic PET scanning

Thoracic positron emission tomography: 18F-fluorodeoxyglucose and beyond

Ongoing technologic and therapeutic advancements in medicine are now testing the limits of conventional anatomic imaging techniques. The ability to image physiology, rather than simply anatomy, is critical in the management of multiple disease processes, especially in oncology. Nuclear medicine has assumed a leading role in detecting, diagnosing, staging and assessing treatment response of various pathologic entities, and appears well positioned to do so into the future. When combined with computed tomography (CT) or magnetic resonance imaging (MRI), positron emission tomography (PET) has become the sine quo non technique of evaluating most solid tumors especially in the thorax. PET/CT serves as a key imaging modality in the initial evaluation of pulmonary nodules, often obviating the need for more invasive testing. PET/CT is essential to staging and restaging in bronchogenic carcinoma and offers key physiologic information with regard to treatment response. A more recent development, PET/MRI, shows promise in several specific lung cancer applications as well. Additional recent advancements in the field have allowed PET to expand beyond imaging with ¹⁸F-flurodeoxyglucose (FDG) alone, now with the ability to specifically image certain types of cell surface receptors. In the thorax this predominantly includes ⁶⁸Ga-DOTATATE which targets the somatostatin receptors abundantly expressed in neuroendocrine tumors, including bronchial carcinoid. This receptor targeted imaging technique permits targeting these tumors with therapeutic analogues such as ¹⁷⁷Lu labeled DOTATATE. Overall, the proper utilization of PET in the thorax has the ability to directly impact and improve patient care.

Rare cause of repeated pulmonary embolism: a case of primary pleural squamous cell carcinoma and literature review

Background

Malignant tumors are risk factors for a pulmonary embolism (PE), and a PE caused by a tumor is not uncommon. Primary pleural squamous cell carcinoma (PPSCC) is a rare malignancy; thus, a related PE is extremely rare.

Case presentation

A previously healthy 49-year-old female patient was admitted to Northern Jiangsu People’s Hospital owing to chest tightness, cough, and breathing difficulty that persisted for 3 days. Following admission, a computed tomography (CT) pulmonary angiography revealed an embolism in the main pulmonary artery, upper and lower pulmonary artery branch. The patient was treated with alteplase, warfarin, and antibiotics. Over the following year, she experienced recurrent chest pain and tightness and breathing difficulty, with multiple CT pulmonary angiography revealing thrombosis in the right and left main pulmonary artery. No abnormalities were observed in surrogate markers of autoimmune diseases, tumor antigen testing, or ultrasonography; thus, the cause of recurrent PE was not identified. Subsequently, a positron emission tomography-computed tomography (PET-CT) examination revealed diffuse heterogeneous thickening of the right pleura and substantially increased glucose metabolism. A CT-guided pleural biopsy was performed, and histopathological examination of the pleura eventually revealed a diagnosis of PPSCC.

Conclusions

PPSCC is a rare tumor that lacks specific clinical manifestations and is difficult to detect with imaging techniques. The occurrence of PE as the primary manifesting symptom in a patient with PPSCC is extremely rare. Thus, malignant tumors should be considered in patients with no risk factors for PE and/or in those with recurrent PE. An immediate diagnosis and adequate intervention can be achieved with increased awareness of this diagnosis and subsequent related examinations.

Image quality and detectability in Siemens Biograph PET/MRI and PET/CT systems-a phantom study

BACKGROUND

The technology of modern positron emission tomography (PET) systems continuously improving, and with it the possibility to detect smaller lesions. Since first introduced in 2010, the number of hybrid PET/magnetic resonance imaging (MRI) systems worldwide is constantly increasing. It is therefore important to assess and compare the image quality, in terms of detectability, between the PET/MRI and the well-established PET/computed tomography (CT) systems. For this purpose, a PET image quality phantom (Esser) with hot spheres, ranging from 4 to 20 mm in diameter, was prepared with fluorodeoxyglucose and sphere-to-background activity concentrations of 8:1 and 4:1, to mimic clinical conditions. The phantom was scanned on a PET/MRI and a PET/CT system for both concentrations to obtain contrast recovery coefficients (CRCs) and contrast-to-noise ratios (CNRs), for a range of reconstruction settings. The detectability of the spheres was scored by three human observers for both systems and concentrations and all reconstructions. Furthermore, the impact of acquisition time on CNR and observer detectability was investigated.

RESULTS

Reconstructions applying point-spread-function modeling (and time-of-flight for the PET/CT) yielded the highest CRC and CNR in general, and PET/CT demonstrated slightly higher values than PET/MRI for most sphere sizes. CNR was dependent on reconstruction settings and was maximized for 2 iterations, a pixel size of less than 2 mm and a 4 mm Gaussian filter. Acquisition times of 97 s (PET/MRI) and 150 s (PET/CT) resulted in similar total net true counts. For these acquisition times, the smallest detected spheres by the human observers in the 8:1 activity concentration was the 6-mm sphere with PET/MRI (CNR = 5.6) and the 5-mm sphere with PET/CT (CNR = 5.5). With an acquisition time of 180 s, the 5-mm sphere was also detected with PET/MRI (CNR = 5.8). The 8-mm sphere was the smallest detected sphere in the 4:1 activity concentration for both systems.

CONCLUSION

In this experimental study, similar detectability was found for the PET/MRI and the PET/CT, although for an increased acquisition time for the PET/MRI.