Computed tomography with energy-resolved detection: a feasibility study

Abstract

The feasibility of computed tomography (CT) with energy-resolved x-ray detection has been investigated. A breast CT design with multi slit multi slice (MSMS) data acquisition was used for this study. The MSMS CT includes linear arrays of photon counting detectors separated by gaps. This CT configuration allows for efficient scatter rejection and 3D data acquisition. The energy-resolved CT images were simulated using a digital breast phantom and the design parameters of the proposed MSMS CT. The phantom had 14 cm diameter and 50/50 adipose/glandular composition, and included carcinoma, adipose, blood, iodine and CaCO3 as contrast elements. The x-ray technique was 90 kVp tube voltage with 660 mR skin exposure. Photon counting, charge (energy) integrating and photon energy weighting CT images were generated. The contrast-to-noise (CNR) improvement with photon energy weighting was quantified. The dual energy subtracted images of CaCO3 and iodine were generated using a single CT scan at a fixed x-ray tube voltage. The x-ray spectrum was electronically split into low- and high-energy parts by a photon counting detector. The CNR of the energy weighting CT images of carcinoma, blood, adipose, iodine, and CaCO3 was higher by a factor of 1.16, 1.20, 1.21, 1.36 and 1.35, respectively, as compared to CT with a conventional charge (energy) integrating detector. Photon energy weighting was applied to CT projections prior to dual energy subtraction and reconstruction. Photon energy weighting improved the CNR in dual energy subtracted CT images of CaCO3 and iodine by a factor of 1.35 and 1.33, respectively. The combination of CNR improvements due to scatter rejection and energy weighting was in the range of 1.71-2 depending on the type of the contrast element. The tilted angle CZT detector was considered as the detector of choice. Experiments were performed to test the effect of the tilting angle on the energy spectrum. Using the CZT detector with 20 degrees tilting angle decreased the tailing of the measured x-ray spectrum as compared to a conventional CZT detector. It was concluded that the energy-resolved MSMS CT with tilted angle CZT detector is potentially feasible and could provide a unique combination of photon counting, energy weighting, scatter rejection and single kVp dual energy subtraction CT imaging.

Achieving Routine Submillisievert CT Scanning: Report from the Summit on Management of Radiation Dose in CT

“…PCDs perform energy discrimination on the basis of an analysis of the height of each measured signal (41)(42)(43)(44)(45). Electronic and Swank noise affect the measured energy for each photon but do not change photon counts.…”

Least squares parameter estimation methods for material decomposition with energy discriminating detectors

“…17 To generate a digital breast phantom, a postmortem specimen was scanned with cone-beam CT and then segmented into glandular and adipose tissues. The conebeam CT system was constructed using a standard x-ray tube ͑Dynamax 78E͒, a rotation stage ͑Kollmorgen Goldline DDR D062M, Danaher Motion, Wood Dale, IL͒, and a flat panel detector ͑Paxscan 4030CB, Varian Medical, Inc., Palo Alto, CA͒.…”

“…Breast imaging is suitable for application in the current photon counting detector technology due to its low dose requirement. [17][18][19] Breast computed tomography with charge integrating flat panel detectors is currently in the clinical trial phase. It has been shown to have advantages over other breast imaging modalities.…”

“…20 Some investigators have proposed using energy discriminating detectors for breast CT to improve image quality and reduce patient dose. 17,18,21 An additional advantage of such a system is the ability to decompose relevant materials in the breast. A four-material decomposition technique is useful in the case of contrast-enhanced breast imaging.…”

Tight‐frame based iterative image reconstruction for spectral breast CT

“…Recent advances in solid state semiconductor materials allow photon-counting and energy discriminating imaging detectors to be used in a breast CT system to produce higher quality images. [1][2][3][4][5][6][7][8][9] Cadmium zinc telluride (CZT) single crystal detectors have been investigated and implemented as x-ray detectors in current breast CT systems. These systems use CZT due to its large effective atomic number (49.6), high mass density (5.8 g/cm 3 ), and higher quantum efficiency.…”