Fusion of respiration-correlated PET and CT scans: correlated lung tumour motion in anatomical and functional scans

Abstract

Lower lobe lung tumours in particular can move up to 2 cm in the cranio-caudal direction during the respiration cycle. This breathing motion causes image artefacts in conventional free-breathing computed tomography (CT) and positron emission tomography (PET) scanning, rendering delineation of structures for radiotherapy inaccurate. The purpose of this study was to develop a method for four-dimensional (4D) respiration-correlated (RC) acquisition of both CT and PET scans and to develop a framework to fuse these modalities. The breathing signal was acquired using a thermometer in the breathing airflow of the patient. Using this breathing signal, the acquired CT and PET data were grouped to the corresponding respiratory phases, thereby obtaining 4D CT and PET scans. Tumour motion curves were assessed in both image modalities. From these tumour motion curves, the deviation with respect to the mean tumour position was calculated for each phase. The absolute position of the centre of the tumour, relative to the bony anatomy, in the RCCT and gated PET scans was determined. This 4D acquisition and 4D fusion methodology was performed for five patients with lower lobe tumours. The peak-to-peak amplitude range in this sample group was 1-2 cm. The 3D tumour motion curve differed less than 1 mm between PET and CT for all phases. The mean difference in amplitude was less than 1 mm. The position of the centre of the tumour (relative to the bony anatomy) in the RCCT and gated PET scan was similar (difference <1 mm) when no atelectasis was present. Based on these results, we conclude that the method described in this study allows for accurate quantification of tumour motion in CT and PET scans and yields accurate respiration-correlated 4D anatomical and functional information on the tumour region.

Short-Term Displacement and Reproducibility of the Breast and Nodal Targets Under Active Breathing Control

“…For each region of interest, alignment to the end exhale state of each session was performed using a 3-D regional rigid alignment tool for translation and rotation developed at the Netherlands Cancer Institute. 16 The alignment was reviewed visually on the axial, coronal, and sagittal planes (Figure 1b) to verify the goodness-of-fit based on anatomy within that ROI. The displacement as a function of breath-hold state was determined for a reference point placed approximately in the center of each region of interest on the exhale dataset.…”

Motion artifacts occurring at the lung/diaphragm interface using 4D CT attenuation correction of 4D PET scans

“…Figure 1 illustrates the imaging artifact that can occur when a 4D PET image is corrected using CTAC data which is out of phase of the 4D PET data. While it has been reported that it is feasible to minimize motion artifacts by using 4D PET corrected by 4D CT in patients in a clinical setting, ( 21 – 23 ) the addition of a 4D CT adds considerable complexity, as well as increased patient dose. As a consequence, clinical centers may avoid these complications by using 4D PET imaging protocols with attenuation correction based on 3D CT. A number of studies have compared different methods for 4D PET attenuation correction in patients ( 21 ) and phantoms, ( 24 – 26 ) as well as simulated data based on 3D PET and 4D CT in patients.…”

Phased Versus Midventilation Attenuation-Corrected Respiration-Correlated PET for Patients with Non-Small Cell Lung Cancer

“…To overcome this shortcoming, several techniques such as respiration-correlated acquisitions have been proposed (10)(11)(12)(13)(14)(15)(16)(17). In respiration-correlated PET (RCPET)/CT (RCCT), the patient's respiratory signal is recorded during the acquisition of the data.…”

“…In respiration-correlated PET (RCPET)/CT (RCCT), the patient's respiratory signal is recorded during the acquisition of the data. Many studies have shown the benefit of respiration-correlated PET for a fixed number of phases in terms of improved volume recovery and SUV quantification for moving tumors (11,12,15,17).…”