Elsevier

Clinical Positron Imaging

Volume 3, Issue 6, November–December 2000, Pages 223-230
Clinical Positron Imaging

Original article
Combined PET/CT Imaging in Oncology: Impact on Patient Management

https://doi.org/10.1016/S1095-0397(01)00055-3Get rights and content

Abstract

Purpose: In this work, we describe five oncology patients whose clinical management were uniquely benefited by a novel scanner that acquires positron emission tomography (PET) and x-ray computed tomography (CT) in the same imaging session.

Procedures: Co-registered 2-[F18]-fluoro-2-deoxy-D-glucose (FDG)-PET and CT images were acquired using a combined PET/CT scanner. Pathology and clinical follow-up data were used to confirm PET/CT scan results.

Results: The combined PET/CT scanner demonstrated the ability to distinguish malignant lesions from normal physiologic FDG uptake in the striated muscles of the head and neck as well as excretory and bowel activity in the abdomen and pelvis. Additionally, the technology positively affected patient management through localization for surgical and radiation therapy planning as well as assessment of tumor response.

Conclusion: Our experience indicates that simultaneous acquisition of co-registered PET and CT images enabled physicians to more precisely discriminate between physiologic and malignant FDG uptake and more accurately localize lesions, improving the value of diagnostic PET in oncologic applications.

Introduction

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hole-body PET scanning with the radiolabeled glucose analog 2-[F18]-fluoro-2-deoxy-D-glucose (FDG) plays an important role in the diagnosis and management of cancer. FDG accumulation detected by PET has been shown to be a reliable method for assessing the glucose metabolic rate of human cells.1, 2 Given that many malignant cells exhibit elevated glucose metabolism,3 FDG-PET has been used in the primary staging and therapeutic monitoring of cancer. Due to its high sensitivity, FDG-PET can distinguish malignant from benign lesions and can identify areas of cancerous involvement.4 Indeed, FDG-PET can accurately detect a number of different malignancies including lymphoma and melanoma, as well as lung, colorectal, and head and neck tumors.5, 6, 7, 8, 9 However, the clinical interpretation of FDG-PET scans can be confounded by normal physiologic accumulation of FDG.

Variable physiologic FDG uptake occurs in the digestive tract, thyroid gland, striated muscle, myocardium, bone marrow, brain and genitourinary tract.10, 11 In particular, the neck, abdomen and pelvis can be challenging areas to distinguish physiologic muscle and organ uptake from tumor. While knowledge of the normal distribution of FDG uptake is paramount to the accurate interpretation of whole-body PET images, it is often difficult to confidently identify an area as normal or pathologic with the limited anatomic landmarks provided by PET alone. This fact, coupled with the benefit of localization for proper staging and surgical planning, necessitates the use of anatomic images in the evaluation of PET studies.

Normal physiologic uptake in an FDG-PET scan may be misinterpreted as a false positive result or mask a nearby malignant lesion. It has been shown that the visual correlation of PET with CT can improve the accuracy of PET alone.12 Furthermore, CT or magnetic resonance (MR) images have been retrospectively fused to simultaneously display registered anatomic and metabolic information.13 Fusion images can improve the accuracy of tumor detection over visual correlation of the two images separately,14, 15 however, the repositioning of the patient and time interval between scans makes the co-registration of separately obtained images difficult and inherently imprecise.

In order to realize the benefits of anatomic information while addressing the problems associated with retrospective image fusion, a novel combined PET/CT scanner has been built.16 With the combined PET/CT scanner, the patient undergoes a spiral CT scan followed immediately by a PET scan during the same imaging session. This method addresses the patient repositioning and temporal problems associated with retrospective fusion methods, providing more precise co-registration of the two images. Additionally, the CT scan can be used to provide low noise PET attenuation correction factors and scatter correction, thus improving quantitative PET imaging crucial for serial studies assessing tumor response to therapy.17

We illustrate five clinical situations where the combined PET/CT tomograph was critical to the accurate interpretation of PET data. Specific examples of physiologic FDG uptake are illustrated and the ability of PET/CT to discriminate tumor from normal uptake is addressed. Additionally, we discuss the impact of the combined PET/CT on the patients' surgical and medical management.

Section snippets

PET/CT Scanner and Acquisition

The novel combined PET/CT scanner used in this work is described in detail by Beyer et al.16 Briefly, the combined PET/CT tomograph is comprised of a Siemens Somatom AR.SP spiral CT and a partial ring, rotating ECAT ART PET scanner housed in a single gantry. PET and CT images can be acquired for an axial extent of 100cm, which is sufficient to allow scanning from the chin to the lower thigh. The scanning session begins after the injection of the desired radiolabeled tracer with a 5–10 min CT

Case 1

This 34-y-old man was diagnosed with squamous cell carcinoma of the right hard palate and gingiva in December of 1998. Tumor resection was performed and chemotherapy and radiation therapy were subsequently administered. Recurrence diagnosed 7 mo later in the right cheek and neck was surgically treated with a right maxillectomy. Radiation and chemotherapy were again administered. In February of 2000, a follow-up CT of the head and neck revealed abnormal enhancement involving the right parotid,

Discussion

The cases presented in this report demonstrate some of the benefits that may be realized by combined PET/CT imaging. By acquiring both images in the same session, the patient does not need to be moved from the scanning bed, thus eliminating changes in position that lead to misregistration of PET and CT images. This becomes particularly important for head and neck imaging, where changes in neck position have been shown to affect retrospective fusion of PET and MRI images and result in

Conclusion

The cases illustrated in this review suggest that PET and CT images acquired in the same scanning session by a PET/CT scanner may improve both the accuracy and utility of PET image interpretation. In our experience, these accurately co-registered PET and CT images have helped to discriminate areas of physiologic uptake from malignant lesions in situations where conventional PET or CT alone was equivocal. In addition, the PET/CT scanner eliminates the co-registration of a PET scan with anatomic

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