Optimization of dual‐energy imaging systems using generalized NEQ and imaging task

Abstract

Dual-energy (DE) imaging is a promising advanced application of flat-panel detectors (FPDs) with a potential host of applications ranging from thoracic and cardiac imaging to interventional procedures. The performance of FPD-based DE imaging systems is investigated in this work by incorporating the noise-power spectrum associated with overlying anatomical structures ("anatomical noise" modeled according to a 1/f characteristic) into descriptions of noise-equivalent quanta (NEQ) to yield the generalized NEQ (GNEQ). Signal and noise propagation in the DE imaging chain is modeled by cascaded systems analysis. A Fourier-based description of the imaging task is integrated with the GNEQ to yield a detectability index used as an objective function for optimizing DE image reconstruction, allocation of dose between low- and high-energy images, and selection of low- and high-kVp. Optimal reconstruction and acquisition parameters were found to depend on dose; for example, optimal kVp varied from [60/150] kVp at typical radiographic dose levels (approximately 0.5 mGy entrance surface dose, ESD) but increased to [90/150] kVp at high dose (ESD approximately 5.0 mGy). At very low dose (ESD approximately 0.05 mGy), detectability index indicates an optimal low-energy technique of 60 kVp but was largely insensitive to the choice of high-kVp in the range 120-150 kVp. Similarly, optimal dose allocation, defined as the ratio of low-energy ESD and the total ESD, varied from 0.2 to 0.4 over the range ESD=(0.05-5.0) mGy. Furthermore, two applications of the theoretical framework were explored: (i) the increase in detectability for DE imaging compared to conventional radiography; and (ii) the performance of single-shot vs double-shot DE imaging, wherein the latter is found to have a DQE approximately twice that of the former. Experimental and theoretical analysis of GNEQ and task-based detectability index provides a fundamental understanding of the factors governing DE imaging performance and offers a framework for system design and optimization.

Task-based modeling and optimization of a cone-beam CT scanner for musculoskeletal imaging

“…The detectability index has been used as an objective function for system optimization in a variety of applications 30,37,44 and Gang et al 10 have demonstrated reasonable correspondence with real observer performance for simple imaging tasks. The work of Gang et al 10 formed an important theoretical=experimental justification for the current work and provided confidence that the trends and optima computed in this paper will bear correspondence with real observer performance for simple imaging tasks.…”

“…Early work involved application of cascaded systems analysis in modeling of indirect and direct-detection FPDs, 3,4 extended to descriptions of mammography 35 and angiography, 7,19 dual-energy imaging, 36,37 tomosynthesis, 15 and CBCT. 5,30 Variations include incorporation of various system factors (viz., magnification, focal spot size, and x-ray scatter) [16][17][18] and generalization to include noise factors other than quantum noise (viz., anatomical background clutter).…”

Noise aliasing and the 3D NEQ of flat-panel cone-beam CT: Effect of 2D/3D apertures and sampling

“…These descriptors have become common for 2D imaging systems, may be determined by experimental measurements 1,2 and by theoretical calculations ͑e.g., cascaded systems analysis͒, [3][4][5] and have been proven useful in system design and optimization. [6][7][8][9][10][11][12][13][14][15][16][17] These metrics can be described similar to 3D imaging, including tomosynthesis and CBCT. [18][19][20][21][22][23][24][25] With a knowledge of the imaging task and an appropriate model observer, these metrics can be extended to a description of task performance as described by ICRU Report No.…”

Dual-Energy CT with Fast-kVp Switching and Its Applications in Orthopedics

“…This lends itself to imaging that requires high light output, fast primary speed, very low afterglow. Gemstone has a primary speed of only 30 ns, or 100 times faster than GOS (Gd 2 O 2 S), while also having afterglow that is only 20% of GOS, making it ideal for fast sampling [16]. The capabilities of the scintillator are also paired with an ultrafast data acquisition system (up to 7 enabling simultaneous acquisition of low-and high-kVp data at customary rotation speeds.…”