Soft tissue imaging with photon counting spectroscopic CT

Abstract

The purpose of this work was experimental investigation of photon counting spectroscopic CT (PCS-CT) imaging of anatomical soft tissue with clinically relevant size. The imaging experiments were performed using a spectroscopic CT system based on CdZnTe photon counting detector with two rows of pixels, 256 pixels in each row, 1 × 1 mm(2) pixel size, and 25.6 cm detector length. The detector could split the x-ray energy spectrum to 5 regions (energy bins), and acquire 5 multi-energy (spectroscopic) CT images in a single CT scan. A sample of round shaped anatomical soft tissue of 14 cm diameter including lean and fat was used for imaging. To avoid the negative effect of anatomical noise on quantitative analysis, a spectroscopic CT phantom with tissue equivalent solid materials was used. The images were acquired at 60, 90, and 120 kVp tube voltages, and spectroscopic image series were acquired with 3 and 5 energy bins. Spectroscopic CT numbers were introduced and used to evaluate an energy selective image series. The anatomical soft tissue with 14 cm diameter was visualized with good quality and without substantial artifacts by the photon counting spectroscopic CT system. The effects of the energy bin crosstalk on spectroscopic CT numbers were quantified and analyzed. The single and double slice PCS-CT images were acquired and compared. Several new findings were observed, including the effect of soft tissue non-uniformity on image artifacts, unique status of highest energy bin, and material dependent visualization in spectroscopic image series. Fat-lean decomposition was performed using dual energy subtraction and threshold segmentation methods, and compared. Using K-edge filtered x-rays improved fat-lean decomposition as compared to conventional x-rays. Several new and important aspects of the PCS-CT were investigated. These include imaging soft tissue with clinically relevant size, single- and double-slice PCS-CT imaging, using spectroscopic CT numbers to quantify multi-energy PCS-CT images, application of K-edge filtered x-rays for improved soft tissue decomposition, and several others. The study suggests that the presented PCS-CT technology meets the requirements of a particular clinical application, i.e. dedicated breast CT.

Photon-counting CT: Technical Principles and Clinical Prospects

“…Breast CT.-Currently, PCDs are being used on an experimental basis in dedicated breast CT systems (62,63). High spatial resolution is an advantage in breast imaging, which must depict small features and subtle lesions.…”

Photon-counting Detector CT: System Design and Clinical Applications of an Emerging Technology

“…However, PCD CT systems count each individual photon equally, regardless of the measured photon energy. Hence, the low-energy photons contribute more to the image contrast for PCD CT than for EID CT, which improves the image contrast and contrast-to-noise ratio of iodine contrast material (9)(10)(11)(12)(13)(40)(41)(42)(43)(44)(45)(46)(47)(48). The increased iodine contrast can be observed for different patient sizes, ranging from newborns to large adults, and is more pronounced for higher tube potentials, such as 120 or 140 kV (19).…”

MARS-MD: rejection based image domain material decomposition

“…Clinical dual-energy CT is typically performed using either dual-source [1], kVp switching [2][3][4], or dual-layered detectors [5,6]. More recently there has been development of pre-clinical systems which utilise energy discriminating photon counting detectors to provide up to eight channels of energy information [7][8][9][10]. The MARS (Medipix All Resolution System) is a spectral CT system based on the Medipix3RX photon counting detector.…”