Augmented Whole-Body Scanning via Magnifying PET

Abstract

A novel technique, called augmented whole-body scanning via magnifying PET (AWSM-PET), that improves the sensitivity and lesion detectability of a PET scanner for whole-body imaging is proposed and evaluated. A Siemens Biograph Vision PET/CT scanner equipped with one or two high-resolution panel-detectors was simulated to study the effectiveness of AWSM-PET technology. The detector panels are located immediately outside the scanner's axial field-of-view (FOV). A detector panel contains 2 ×8 detector modules each consisting of 32 ×64 LSO crystals ( 1.0 ×1.0 ×10.0 mm³ each). A ²²Na point source was stepped across the scanner's FOV axially to measure sensitivity profiles at different locations. An elliptical torso phantom containing 7×9 spherical lesions was imaged at different axial locations to mimic a multi-bed-position whole-body imaging protocol. Receiver operating characteristic (ROC) curves were analyzed to evaluate the improvement in lesion detectability by the AWSM-PET technology. Experimental validation was conducted using an existing flat-panel detector integrated with a Siemens Biograph 40 PET/CT scanner to image a torso phantom containing spherical lesions with diameters ranging from 3.3 to 11.4 mm. The contrast-recovery-coefficient (CRC) of the lesions was evaluated for the scanner with or without the AWSM-PET technology. Monte Carlo simulation shows 36%-42% improvement in system sensitivity by a dual-panel AWSM-PET device. The area under the ROC curve is 0.962 by a native scanner for the detection of 4 mm diameter lesions with 5:1 tumor-to-background activity concentration. It was improved to 0.977 and 0.991 with a single- and dual-panel AWSM-PET system, respectively. Experimental studies showed that the average CRC of 3.3 mm and 4.3 mm diameter tumors were improved from 2.8% and 4.2% to 7.9% and 11.0%, respectively, by a single-panel AWSM-PET device. With a high-sensitivity dual-panel device, the corresponding CRC can be further improved to 11.0% and 15.9%, respectively. The principle of the AWSM-PET technology has been developed and validated. Enhanced system sensitivity, CRC and tumor detectability were demonstrated by Monte Carlo simulations and imaging experiments. This technology may offer a cost-effective path to realize high-resolution whole-body PET imaging clinically.

Fig. 1.

(a) A basic AWSM-PET system consists of high-resolution detectors (an Outsert) placed outside the scanner’s axial FOV to survey the body in conjunction with scanner detectors. At the first bed position, the three tumors (represented by red circles) are in the native scanner’s imaging FOV. When the patient is moved to the second bed position, these tumors are outside the scanner’s FOV but inside the augmented zone 1. These additional coincidence events detected by an Outsert are information-rich. Joint image reconstruction using SS events from the bed position 1 and OS events from bed position 2 can enhance both the image resolution and system sensitivity. (b). An AWSM-PET system with dual-panel Outserts creates additional augmented zones 2 and 3 to further improve the sensitivity and image resolution of the scanner.

Fig. 2.

(a) AWSM-PET with one Outsert detector; (b) AWSM-PET with dual-Outsert; (c) Tumor pattern simulated in an elliptical torso phantom and definition of tumor region numbers.

Fig. 3.

(a) Setup of the torso phantom imaging experiment with a flat-panel detector placed outside a scanner’s axial FOV; (b) Photo showing the fillable lesions of different sizes. For each size group, only three lesions were filled with blue dyes and radioactivity. The others were filled with water. All lesions were aligned to be visible in the same image slice.

Fig. 4.

Sensitivity profiles at different positions across the axial FOV for (a) a single-panel AWSM-PET system as shown in Fig. 2(a), and (b) a dual-panel AWSM-PET system as shown in Fig. 2(b).

Fig. 5.

(a) Reconstructed images of a torso phantom containing 63 lesions (4 mm in diameter, T/B = 5) measured by a simulated Siemens Biograph Vision PET/CT scanner, and the same scanner equipped with one Outsert or dual Outserts as shown in Fig. 2; (b) ROC curves of the three systems; (c) Average CRCs of the 7 tumors in each group as a function of different regions for all images in (a).

Fig. 6.

(a) Reconstructed images using events from 232- and 264- second scans with the native scanner. (b) ROC curves of the five different configurations.

Fig. 7.

(a)Reconstructed images of the torso phantom in Fig. 3 (T/B = 6) imaged by a native Biograph 40 PET/CT scanner or the same scanner equipped with a single-Outsert, with dual-Outserts, or dual-Outserts that have higher sensitivity; (b) Average CRCs measured by the above four configurations are shown as a function of the lesion sizes.