A second‐generation virtual‐pinhole PET device for enhancing contrast recovery and improving lesion detectability of a whole‐body PET/CT scanner

Abstract

Purpose We have developed a second‐generation virtual‐pinhole (VP) positron emission tomography (PET) device that can position a flat‐panel PET detector around a patient's body using a robotic arm to enhance the contrast recovery coefficient (CRC) and detectability of lesions in any region‐of‐interest using a whole‐body PET/computed tomography (CT) scanner. Methods We constructed a flat‐panel VP‐PET device using 32 high‐resolution detectors, each containing a 4 × 4 MPPC array and 16 × 16 LYSO crystals of 1.0 × 1.0 × 3.0 mm3 each. The flat‐panel detectors can be positioned around a patient's body anywhere in the imaging field‐of‐view (FOV) of a Siemens Biograph 40 PET/CT scanner by a robotic arm. New hardware, firmware and software have been developed to support the additional detector signals without compromising a scanner's native functions. We stepped a 22Na point source across the axial FOV of the scanner to measure the sensitivity profile of the VP‐PET device. We also recorded the coincidence events measured by the scanner detectors and by the VP‐PET detectors when imaging phantoms of different sizes. To assess the improvement in the CRC of small lesions, we imaged an elliptical torso phantom measuring 316 × 228 × 162 mm3 that contains spherical tumors with diameters ranging from 3.3 to 11.4 mm with and without the VP‐PET device. Images were reconstructed using a list mode Maximum‐Likelihood Estimation‐Maximization algorithm implemented on multiple graphics processing units (GPUs) to support the unconventional geometries enabled by a VP‐PET system. The mean and standard deviation of the CRC were calculated for tumors of different sizes. Monte Carlo simulation was also conducted to image clusters of lesions in a torso phantom using a PET/CT scanner alone or the same scanner equipped with VP‐PET devices. Receiver operating characteristic (ROC) curves were analyzed for three system configurations to evaluate the improvement in lesion detectability by the VP‐PET device over the native PET/CT scanner. Results The repeatability in positioning the flat‐panel detectors using a robotic arm is better than 0.15 mm in all three directions. Experimental results show that the average CRC of 3.3, 4.3, and 6.0 mm diameter tumors was 0.82%, 2.90%, and 5.25%, respectively, when measured by the native scanner. The corresponding CRC was 2.73%, 6.21% and 10.13% when imaged by the VP‐PET insert device with the flat‐panel detector under the torso phantom. These values may be further improved to 4.31%, 9.65% and 18.01% by a future dual‐panel VP‐PET insert device if DOI detectors are employed to triple its detector efficiency. Monte Carlo simulation results show that the tumor detectability can be improved by a VP‐PET device that has a single flat‐panel detector. The improvement is greater if the VP‐PET device employs a dual‐panel design. Conclusions We have developed a prototype flat‐panel VP‐PET device and integrated it with a clinical PET/CT scanner. It significantly enhances the contrast of lesions, especially for those that are ...

Self-Collimating SPECT With Multi-Layer Interspaced Mosaic Detectors

“…A separate preliminary study we conduct shows that the events from different detector layers all contribute, although differently in terms of their resolution property and statistical quantity, towards improving the image quality. This finding is consistent with the image resolution and SNR improvement reported on virtual pinhole PET [36,45] and zoom-in PET [37] when events with variable resolution properties are involved.…”

Design and performance simulation studies of a breast PET insert integrable into a clinical whole-body PET/MRI scanner

“…The proposed insert will induce additional attenuation in the whole-body scanner FOV, which will degrade the PET performance characteristics in terms of the sensitivity and spatial resolution of the whole-body PET modality by opaque LORs and scattering at the insert, thus, an accurate attenuation correction must be implemented. However, placing a PET insert inside a whole-body PET scanner opens up the possibility of recording PET-PET coincidences between the insert and scanner, which could be used to improve the spatial resolution outside the insert FOV through the virtual pinhole effect (Tai et al 2008, Mathews et al 2013, Jiang et al 2019.…”

Augmented Whole-Body Scanning via Magnifying PET

“…The axial FOV of the scanner is 220 mm. The integration of the flatpanel detector with the scanner, including readout electronics and data acquisition were described and can be found in [30].…”

“…Approaches that bring the benefits of organ-specific PET to a clinical PET/CT scanner have emerged in recent years and been independently validated [22][23][24][25], including multi-resolution PET [26,27], zoom-in PET [28], and virtual-pinhole PET (VP-PET) [23]. We previously developed several prototype VP-PET insert systems and demonstrated its ability to improve the image resolution of a clinical PET/CT scanner without compromising its whole-body imaging capability [29,30]. Although the VP-PET insert technique enables zoom-in imaging for an organ-of-interest, it does not directly benefit whole-body cancer staging where the location of a distant metastasis, and thus the "target" region to zoom-in on, is unknown.…”