Translational molecular imaging for cancer

Abstract

Although most clinical diagnostic imaging studies employ anatomic techniques such as computed tomography (CT) and magnetic resonance (MR) imaging, much of radiology research currently focuses on adapting these conventional methods to physiologic imaging as well as on introducing new techniques and probes for studying processes at the cellular and molecular levels in vivo, i.e. molecular imaging. Molecular imaging promises to provide new methods for the early detection of cancer and support for personalized cancer therapy. Although molecular imaging has been practiced in various incarnations for over 20 years in the context of nuclear medicine, other imaging modalities have only recently been applied to the noninvasive assessment of physiology and molecular events. Nevertheless, there has been sufficient experience with specifically targeted contrast agents and high-resolution techniques for MR imaging and other modalities that we must begin moving these new technologies from the laboratory to the clinic. This brief review outlines several of the more promising areas of pursuit in molecular imaging for oncology with an emphasis on those that show the most immediate likelihood for clinical translation.

Figure 1

Modalities for molecular imaging.

Figure 2

Use of a lymphotropic MR contrast agent (iron oxide-containing nanoparticle) in a patient with prostate cancer. Arrows indicate micrometastases, i.e. where nanoparticles are excluded from lymph node uptake (from reference [25]).

Figure 3

FDG-PET images of tumor-bearing rats before and after 12 days of therapy with 3-bromopyruvate (from reference [46]).

Figure 4

SPECT-CT imaging of [¹²⁵I]DCIT in an LNCaP and PC-3 tumor-bearing SCID mouse. The PSMA-expressing LNCaP tumor displays high uptake while the PSMA non-expressing PC-3 tumor shows minimal uptake (adapted from reference [18]).

Figure 5

MicroPET images obtained 3 h post injection with ⁶⁸Ga-F(ab) ₂-Herceptin in a mouse with a BT 474 breast tumor (images provided courtesy Steven Larson, Memorial Sloan Kettering Cancer Center). Note the early metabolic response to therapy with 17-allylamino-17-demethoxygeldanamycin (17-AAG).

Figure 6

Amide proton transfer imaging (APTI) in 9L tumors in rat. Both conventional (T2-weighted and apparent diffusion coefficient (ADC) maps) and APTI are shown. Note that the hyperintensity within the peritumoral tissue (small arrow) and cerebrospinal fluid (open arrows) in the ADC map become normal with APTI, adding to the clearer contour of the tumor (large arrow) on the latter images. APTI provides clearer tumor contour than the T2-weighted image as well (adapted from reference [92]).

Figure 7

SPECT imaging of ^99mTc-annexin V in a patient with follicular lymphoma. Note high uptake in tumor-bearing lymph nodes after radiation therapy (from reference [98]).