Metabolic positron emission tomography imaging in cancer detection and therapy response

Abstract

Positron emission tomography (PET) is a noninvasive imaging technique that provides a functional or metabolic assessment of normal tissue or disease conditions. Fluorine 18-fluorodeoxyglucose PET imaging (FDG-PET) is widely used clinically for tumor imaging due to increased glucose metabolism in most types of tumors, and has been shown to improve the diagnosis and subsequent treatment of cancers. We review its use in cancer diagnosis, staging, restaging, and assessment of response to treatment. In addition, other metabolic PET imaging agents in pre-clinical research or clinical trial stages of development are discussed, including amino acid analogs based on increased protein synthesis, and choline, which is based on increased membrane lipid synthesis. Amino acid analogs and choline are more specific to tumor cells than FDG, so they play an important role in differentiating cancers from benign conditions and in the diagnosis of cancers with low FDG uptake or high background FDG uptake. For decades, researchers have shown that tumors display altered metabolic profiles with elevated uptake of glucose, amino acids, and lipids. This can be used for cancer diagnosis and monitoring of the therapeutic response with excellent signal-to-noise ratios.

Figure 1

FDG-PET/CT scans of a 63 year-old female with stage IVA adenocarcinoma of the lung before and after 2 cycles of carboplatin and pemetrexed. Left panel images are pretreatment images (A, B, C and D), while the right panel are posttreatment images (E, F, G and H). The images from top to bottom are CT transaxials (A, E), CT and PET fused transaxials (B, F), PET transaxials (C, G), and maximum intensity projection images (D, H).

Figure 2

FDG-PET/CT scans of a 41 year-old male with right base of tongue squamous cell carcinoma before and after post-operative cisplatin and radiation. There is a persistent, incidental hypermetabolic lesion in the right lobe of the thyroid gland. Left panel images are pretreatment images (A, B, C and D), while the right panel are posttreatment images (E, F, G and H). The images from top to bottom are CT transaxials (A, E), CT and PET fused transaxials (B, F), PET transaxials (C, G), and maximum intensity projection images (D, H).

Figure 3

Coronal PET (A) and CT fused (B) anti-¹⁸F-FACBC images in a 71-year-old man (restaging) with biopsy-proven prostate bed recurrence extending toward the left seminal vesicle (arrow in A). Maximum-intensity-projection (MIP) image at 20 min (C) demonstrates uptake in the prostate bed (arrow) but little bladder uptake (arrowhead).

Figure 4

A 58-year-old man with meningioma. (A) T1-weighted gadolinium-enhanced MRI shows an enhanced lesion in the right lateral ventricle. (B) A ¹¹C-choline PET image obtained at 5 min post injection demonstrates increased tumor uptake of ¹¹C-choline and a tumor to white matter (T/W) ratio of 29.10. (C) An FDG-PET image obtained at 50 min post injection shows a tumor with a T/W ratio of 1.65.