Ultra-High Spatial Resolution, Multi-Energy CT using Photon Counting Detector Technology

Abstract

Two ultra-high-resolution (UHR) imaging modes, each with two energy thresholds, were implemented on a research, whole-body photon-counting-detector (PCD) CT scanner, referred to as sharp and UHR, respectively. The UHR mode has a pixel size of 0.25 mm at iso-center for both energy thresholds, with a collimation of 32 × 0.25 mm. The sharp mode has a 0.25 mm pixel for the low-energy threshold and 0.5 mm for the high-energy threshold, with a collimation of 48 × 0.25 mm. Kidney stones with mixed mineral composition and lung nodules with different shapes were scanned using both modes, and with the standard imaging mode, referred to as macro mode (0.5 mm pixel and 32 × 0.5 mm collimation). Evaluation and comparison of the three modes focused on the ability to accurately delineate anatomic structures using the high-spatial resolution capability and the ability to quantify stone composition using the multi-energy capability. The low-energy threshold images of the sharp and UHR modes showed better shape and texture information due to the achieved higher spatial resolution, although noise was also higher. No noticeable benefit was shown in multi-energy analysis using UHR compared to standard resolution (macro mode) when standard doses were used. This was due to excessive noise in the higher resolution images. However, UHR scans at higher dose showed improvement in multi-energy analysis over macro mode with regular dose. To fully take advantage of the higher spatial resolution in multi-energy analysis, either increased radiation dose, or application of noise reduction techniques, is needed.

Keywords: Computed tomography (CT); dual energy; high resolution; photon counting detector (PCD).

Figures

Figure 1

The read out of the low (green) and high (red) energy thresholds at 3 acquisition modes: macro, sharp and UHR, and their corresponding collimations. Native detector pixels are delineated by the dashed lines.

Figure 2

MicroCT and PCCT low-energy threshold images of a mixed stone scanned with sharp mode and reconstructed with 3 different kernels.

Figure 3

Images of a mixed stone scanned with macro and sharp modes and reconstructed with a D50 kernel.

Figure 4

Photo and volume rendered images of a star-shaped lung nodule scanned with macro and sharp mode.

Figure 5

CTR maps of a mixed composition kidney stone scanned with sharp and UHR modes, reconstructed with D50 and S80 kernels.

Figure 6

Threshold low images (gray scale) and CTR map (color) of a mixed stone scanned with UHR mode and 30.4 mGy.