Dual-Modality Imaging of Cancer with SPECT/CT

TLDR

Dual‑modality imaging combines CT and radionuclide imaging on a single gantry to provide simultaneous structural and functional data in one session, a capability not achievable with separate systems. The study evaluates whether a UCSF‑developed SPECT/CT system improves assessment of prostate cancer patients using 111In‑ProstaScint, a radiolabeled antibody targeting PSMA. 111In‑ProstaScint images are reconstructed with an iterative ML‑EM algorithm that corrects for photon attenuation using a patient‑specific CT‑derived attenuation map, accounts for dual‑photon emission and collimator geometry, and then coregisters the radionuclide image onto the CT for enhanced localization. ML‑EM reconstruction with attenuation and collimator corrections produces higher‑quality SPECT/CT images than conventional filtered backprojection, illustrating dual‑modality imaging’s potential to improve disease staging, treatment planning, and response monitoring in cancer patients.

Abstract

Dual-modality imaging is an in vivo diagnostic technique that obtains structural and functional information directly from patient studies in a way that cannot be achieved with separate imaging systems alone. Dual-modality imaging systems are configured by combining computed tomography (CT) with radionuclide imaging (using positron emission tomography (PET) or single-photon emission computed tomography (SPECT)) on a single gantry which allows both functional and structural imaging to be performed during a single imaging session without having the patient leave the imaging system. A SPECT/CT system developed at UCSF is being used in a study to determine if dual-modality imaging offers advantages for assessment of patients with prostate cancer using 111 In-ProstaScint®, a radiolabeled antibody for the prostate-specific membrane antigen. 111 In-ProstaScint® images are reconstructed using an iterative maximum-likelihood expectation-maximization (ML-EM) algorithm with correction for photon attenuation using a patient-specific map of attenuation coefficients derived from CT. The ML-EM algorithm accounts for the dual-photon nature of the 111 In-labeled radionuclide, and incorporates correction for the geometric response of the radionuclide collimator. The radionuclide image then can be coregistered and overlaid in color on a grayscale CT image for improved localization of the functional information from SPECT. Radionuclide images obtained with SPECT/CT and reconstructed using ML-EM with correction for photon attenuation and collimator response improve image quality in comparison to conventional radionuclide images obtained with filtered backprojection reconstruction. These results illustrate the potential advantages of dual-modality imaging for improving the quality and the localization of radionuclide uptake for staging disease, planning treatment, and monitoring therapeutic response in patients with cancer.