From PET detectors to PET scanners

This review describes the properties of available and emerging radiation detector and read-out technologies and discusses how they may affect PET scanner performance. After a general introduction, there is a section in which the physical properties of several different detector scintillators are compared. This is followed by a discussion of recent advances in read-out electronics. Finally, the physical performance of the several commercial PET scanners is summarized.     

PET and PET/CT in pediatric oncology

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and FDG-PET/computed tomography (CT) are becoming increasingly important imaging tools in the noninvasive evaluation and monitoring of children with known or suspected malignant diseases. In this review, we discuss the preparation of children undergoing PET studies and review radiation dosimetry and its implications for family and caregivers. We review the normal distribution of 18F-fluorodeoxyglucose (FDG) in children, common variations of the normal distribution, and various artifacts that may arise. We show that most tumors in children accumulate and retain FDG, allowing high-quality images of their distribution and pathophysiology. We explore the use of FDG-PET in the study of children with the more common malignancies, such as brain neoplasms and lymphomas, and the less-common tumors, including neuroblastomas, bone and soft-tissue sarcomas, Wilms' tumors, and hepatoblastomas. For comparison, other PET tracers are included because they have been applied in pediatric oncology. Multiple multicenter trials are underway that use FDG-PET in the management of children with neoplastic disease; these studies should give us greater insight into the impact FDG-PET can make in their care. PET is emerging as an important diagnostic imaging tool in the evaluation of pediatric cancers. The recent advent of dual-modality PET-computed tomography (PET/CT) imaging systems has added unprecedented diagnostic capability by revealing the precise anatomical localization of metabolic information and metabolic characterization of normal and abnormal structures. The use of CT transmission scanning for attenuation correction has shortened the total acquisition time, which is an especially desirable attribute in pediatric imaging. Moreover, expansion of the regional distribution of the most common PET radiotracer, FDG, and the introduction of mobile PET units have greatly increased access to this powerful diagnostic imaging technology. Here, we review the clinical applications of PET and PET/CT in pediatric oncology. General considerations in patient preparation and radiation dosimetry will be discussed.     

PET and PET/CT in endocrine tumours

Functional information provided by PET tracers together with the superior image quality and the better data quantification by PET technology had a changing effect on the significance of nuclear medicine in medical issues. Recently introduced hybrid PET/CT systems together with the introduction of novel PET radiopharmaceuticals have contributed to the fact that nuclear medicine has become a growing diagnostic impact on endocrinology. In this review imaging strategies, different radiopharmaceuticals including the basic mechanism of their cell uptake, and the diagnostic value of PET and PET/CT in endocrine tumours except differentiated thyroid carcinomas will be discussed.     

PET instrumentation

PET is a nuclear medicine imaging modality and belongs to the family of emission CT, which also includes single-photon emission CT. PET measures the physiologic function inside the human body by measuring the concentration of a radioactively-labeled compound that is taken up by and accumulated in the body's organs. This article discusses the instrumentation used in PET.     

Breast cancer detection using high-resolution breast PET compared to whole-body PET or PET/CT

Purpose

To compare the performance characteristics of positron emission mammography (PEM) with those of whole-body PET (WBPET) and PET/CT in women with newly diagnosed breast cancer.

Methods

A total of 178 women consented to PEM for presurgical planning in an IRB-approved protocol and also underwent either WBPET (n?=?69) or PET/CT (n?=?109) imaging, as per usual care at three centers. Tumor detection sensitivity, positive predictive values, and ¹⁸F-fluorodeoxyglucose (FDG) uptake were compared between the modalities. The effects of tumor size, type, and grade on detection were examined. The chi-squared or Fisher’s exact tests were used to compare distributions between groups, and McNemar’s test was used to compare distributions for paired data within subject groups, i.e. PEM versus WBPET or PEM versus PET/CT.

Results

The mean age of the women was 59?±?12 years (median 60 years, range 26–89 years), with a mean invasive index tumor size of 1.6?±?0.8 cm (median 1.5 cm, range 0.5–4.0 cm). PEM detected more index tumors (61/66, 92 %) than WBPET (37/66, 56 %; p?<?0.001) or PET/CT (95/109, 87 % vs. 104/109, 95 % for PEM; p?<?0.029). Sensitivity for the detection of additional ipsilateral malignancies was also greater with PEM (7/15, 47 %) than with WBPET (1/15, 6.7 %; p?=?0.014) or PET/CT (3/23, 13 % vs. 13/23, 57 % for PEM; p?=?0.003). Index tumor detection decreased with decreasing invasive tumor size for both WBPET (p?=?0.002) and PET/CT (p?<?0.001); PEM was not significantly affected (p?=?0.20). FDG uptake, quantified in terms of maximum PEM uptake value, was lowest in ductal carcinoma in situ (median 1.5, range 0.7–3.0) and invasive lobular carcinoma (median 1.5, range 0.7–3.4), and highest in grade III invasive ductal carcinoma (median 3.1, range 1.4–12.9).

Conclusion

PEM was more sensitive than either WBPET or PET/CT in showing index and additional ipsilateral breast tumors and remained highly sensitive for tumors smaller than 1 cm.     

F-FDG PET and PET/CT in Burkitt's lymphoma

Objective

To explore the value of ¹⁸F fluorodeoxy-glucose (FDG) positron emission tomography (PET) in Burkitt's lymphoma.

Methods

All Burkitt's lymphoma patients referred for FDG PET or FDG PET/computed tomography (CT) exams at our institution from June 2003 to June 2006 were included. Selected patients were followed and clinical information was reviewed retrospectively. Results from FDG PET-PET/CT, as blindly reviewed by a consensus of two experienced readers, were compared with the status of the disease as determined by other laboratory, clinical and imaging exams and clinical follow-up. FDG PET-PET/CT results were classified as true positive or negative and false positive or negative. The degree of FDG uptake in the positive lesions was semiquantified as maximum standard uptake value (SUVmax).

Results

Fifty-seven FDG PET-PET/CT exams were done in 15 patients. Seven exams were done for initial staging, 8 during and 14 after the completion of therapy, and 28 for disease surveillance. For nodal disease FDG PET-PET/CT was true positive in 8, true negative in 47 and false positive in 2 exams (sensitivity 100%, specificity 96%). For extranodal disease FDG PET-PET/CT was true positive in 6, true negative in 48 and false positive in 3 exams (sensitivity 100%, specificity 94%). The mean SUVmax for the positive nodal lesions was 15.7 (range 6.9-21.7, median 18.5) and for extranodal lesions was 14.2 (range 6.2-24.3, median 12.4).

Conclusions

FDG PET-PET/CT is sensitive for the detection of viable disease in Burkitt's lymphoma. Affected areas demonstrated high degree of uptake that was reversible upon successful implementation of treatment.