Molecular imaging of urogenital diseases

Abstract

There is an expanding and exciting repertoire of PET imaging radiotracers for urogenital diseases, particularly in prostate cancer, renal cell cancer, and renal function. Prostate cancer is the most commonly diagnosed cancer in men. With growing therapeutic options for the treatment of metastatic and advanced prostate cancer, improved functional imaging of prostate cancer beyond the limitations of conventional CT and bone scan is becoming increasingly important for both clinical management and drug development. PET radiotracers, apart from ¹⁸F-FDG, for prostate cancer are ¹⁸F-sodium fluoride, ¹¹C-choline, and ¹⁸F-fluorocholine, and (¹¹C-acetate. Other emerging and promising PET radiotracers include a synthetic l-leucine amino acid analogue (anti-¹⁸F-fluorocyclobutane-1-carboxylic acid), dihydrotestosterone analogue (¹⁸F-fluoro-5α-dihydrotestosterone), and prostate-specific membrane antigen-based PET radiotracers (eg, N-[N-[(S)-1,3-dicarboxypropyl]carbamoyl]-4-¹⁸F-fluorobenzyl-l-cysteine, ⁸⁹Zr-DFO-J591, and ⁶⁸Ga [HBED-CC]). Larger prospective and comparison trials of these PET radiotracers are needed to establish the role of PET/CT in prostate cancer. Although renal cell cancer imaging with FDG-PET/CT is available, it can be limited, especially for detection of the primary tumor. Improved renal cell cancer detection with carbonic anhydrase IX (CAIX)-based antibody (¹²⁴I-girentuximab) and radioimmunotherapy targeting with ¹⁷⁷Lu-cG250 appear promising. Evaluation of renal injury by imaging renal perfusion and function with novel PET radiotracers include p-¹⁸F-fluorohippurate, hippurate m-cyano-p-¹⁸F-fluorohippurate, and rubidium-82 chloride (typically used for myocardial perfusion imaging). Renal receptor imaging of the renal renin-angiotensin system with a variety of selective PET radioligands is also becoming available for clinical translation.

Figure 1

FDG PET/CT in a patient with advanced metastatic prostate cancer with (A) metastases and (B) pelvic and lower lumbar bone metastases.

Figure 2

¹⁸F-NaF PET/CT in a man with prostate cancer with right iliac bone metastasis. Central activity corresponds to benign endplate degenerative change of the L5-S1 junction.

Figure 3

¹⁸F-DCFBC low molecular weight PSMA-based PET/CT imaging of castration-resistant metastatic prostate cancer. (A) MIP, (B) Right Iliac bone metastasis, (C) Small Aorto-caval lymph node.

Figure 4

Coronal view of an FDG PET/CT scan of a patient with right kidney RCC. There is moderately increased FDG activity fusing to a soft tissue mass at the lower pole of the right kidney. There is also intensely FDG avid linear expansile lesion with cortical destruction in the left lateral seventh rib consistent with bone metastasis. The uptake in the primary tumor is similar to uptake in kidney parenchyma but less than in renal collecting system.

Figure 5

Coronal PET/CT images of the heart and kidneys in a healthy human subject 2-5 minutes post IV injection of 500 MBq Rb-82 chloride. Images of the heart and the kidneys were acquired after separate but technically identical bolus injections of ⁸²Rb. Image maximum was set at 400kBq/mL. Time activity curves (Figure 6a) showed that uptake in the kidneys was much higher than uptake in the myocardium.

Figure 6a

Time activity curves derived from a dynamic PET study of the myocardium and kidneys 0 – 5 min after injection of 500 mBq Rb-82 chloride. Dots represent the average of the two kidneys, circles represent the myocardium and the unmarked line represents the input function from the left ventricle.

Figure 6b

Impulse response functions of Rb-82 in the myocardium and kidneys. Dots represent the average of the two kidneys, circles represent the myocardium and unmarked lines represent the monoexponential curve fits to the slow decreasing component of both impulse response functions.