Dual-Modality Imaging of Cancer with SPECT/CT

Abstract

Dual-Modality Imaging of Cancer with SPECT/CTwww.tcrt.org 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.

Minimizing the radiation dose of CT attenuation correction while improving image quality: The case for innovation

“…26,27 SPECT-CT systems can employ a conventional multislice CT system, capable of acquiring high resolution, diagnostic quality data and/or low dose, attenuation correction-specific X-ray tubes. Despite the fact that CT studies have generally more counts than line source attenuation maps, CT-specific artifacts can make PET/ CT more challenging than line source attenuation correction 28 (see Figure 2).…”

Dual-Modality Imaging: More Than the Sum of its Components

“…21,59,[62][63][64] SPECT/CT also has demonstrated advantages for oncologic imaging with single-photon agents. 12,25,40,41,[65][66][67][68][69][70] Both SPECT/CT and PET/CT have demonstrated their ability to facilitate attenuation correction using an x-ray based patientspecific attenuation map that can be produced faster and more accurately than attenuation maps generated with external radionuclide sources. 10,34 Clinical studies are underway to evaluate the applicability of x-ray based correction of photon attenuation, 71 and early results demonstrate improvement in sensitivity, specificity, and predictive accuracy in comparison to SPECT perfusion studies reconstructed without correction for photon attenuation.…”

“…Second, the x-ray data can be used to generate a patient-specific map of attenuation coefficients and other a priori anatomical data which in turn is used to correct the radionuclide data for errors due to photon attenuation, scatter radiation, and other physical effects. 1,21,22,25,27,[42][43][44] In these ways, the x-ray data can be used to improve both the visual quality and the quantitative accuracy of the correlated radionuclide data.…”

“…This technique thereby produces anatomical and functional images with the patient in the same position and during a single procedure, which simplifies the image registration and fusion processes. 1,25,28,32,34,36 In seeking to achieve accurate registration of the anatomical and functional data, dual-modality imaging offers several potential advantages over conventional imaging techniques. 37 First, the radionuclide and x-ray images are supplementary and complementary.…”

“…16,17 With the goal of improving the correlation of different types of image data, other investigators have developed instrumentation which integrate both x-ray and radionuclide imaging is in a single device. 1,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] This technique, often called dual-modality imaging, can combine a PET or SPECT system with a CT scanner, using a common patient table, computer, and gantry so that both the x-ray and radionuclide image data are acquired sequentially without removing the patient from the scanner. This technique thereby produces anatomical and functional images with the patient in the same position and during a single procedure, which simplifies the image registration and fusion processes.…”