Attenuation correction for a combined 3D PET/CT scanner

Abstract

In this work we demonstrate the proof of principle of CT-based attenuation correction of 3D positron emission tomography (PET) data by using scans of bone and soft tissue equivalent phantoms and scans of humans. This method of attenuation correction is intended for use in a single scanner that combines volume-imaging (3D) PET with x-ray computed tomography (CT) for the purpose of providing accurately registered anatomical localization of structures seen in the PET image. The goal of this work is to determine if we can perform attenuation correction of the PET emission data using accurately aligned CT attenuation information. We discuss possible methods of calculating the PET attenuation map at 511 keV based on CT transmission information acquired from 40 keV through 140 keV. Data were acquired on separate CT and PET scanners and were aligned using standard image registration procedures. Results are presented on three of the attenuation calculation methods: segmentation, scaling, and our proposed hybrid segmentation/scaling method. The results are compared with those using the standard 3D PET attenuation correction method as a gold standard. We demonstrate the efficacy of our proposed hybrid method for converting the CT attenuation map from an effective CT photon energy of 70 keV to the PET photon energy of 511 keV. We conclude that using CT information is a feasible way to obtain attenuation correction factors for 3D PET.

Towards quantitative PET/MRI: a review of MR-based attenuation correction techniques

“…511 keV [3,4]. By using the CT images for the purpose of AC, lengthy PET transmission scanning with conventional rod-or point sources (TX-AC) has become obsolete in commercially available PET/CT tomographs.…”

Comparative Assessment of Energy-Mapping Approaches in CT-Based Attenuation Correction for PET

“…In recent years, PET/CT scanners have gained widespread acceptance in the clinical setting since the availability of correlated functional and anatomical images was shown to improve the detection or staging of disease by highlighting areas of increased radiotracer uptake on the anatomical images, whereas regions that look abnormal in the anatomical image can draw attention to a potential area of disease where radiopharmaceutical uptake may be low. In PET/CT systems, attenuation correction is achieved by X-ray transmission scanning using the CT sub-system of the combined unit [9]. CT-based attenuation correction (CTAC) reduces substantially total scanning time and yields much lower statistical noise in the generated attenuation map (µ-map) even when using low-dose CT scanning protocols [10].…”

“…CT-based attenuation correction (CTAC) reduces substantially total scanning time and yields much lower statistical noise in the generated attenuation map (µ-map) even when using low-dose CT scanning protocols [10]. It also eliminates the need for rotating radionuclide transmission sources around the patient but suffers from many drawbacks, including the much higher radiation dose delivered to the patient compared to transmission scanning and the possibility of producing artifacts in the attenuation corrected PET images [9], particularly in the presence of contrast agent [11][12][13] and metallic objects in CT images [14,15].…”

“…These include scaling [17], segmentation [8], hybrid (segmentation/scaling) [9], bilinear calibration curve [16,18], dual-energy decomposition methods [19,20], and quadratic polynomial calibration mapping [21]. The latter was recently proposed by our group and assessed using clinical studies.…”

“…Each of the above-referenced energymapping techniques has advantages and drawbacks and, to the best of our knowledge, a comprehensive comparative assessment of these methods has not been performed yet in a clinical setting. Published reports to date compared only two or at most three methods [8,9,17]. In our previous study, we reported on the comparative assessment of a number of energy-mapping methods using a small sample of clinical datasets where the evaluation was limited to the generated µ-maps only without assessing the impact on the resulting PET images [22].…”