An innovative phantom for quantitative and qualitative investigation of advanced x-ray imaging technologies

Abstract

Development, characterization, and quality assurance of advanced x-ray imaging technologies require phantoms that are quantitative and well suited to such modalities. This note reports on the design, construction, and use of an innovative phantom developed for advanced imaging technologies (e.g., multi-detector CT and the numerous applications of flat-panel detectors in dual-energy imaging, tomosynthesis, and cone-beam CT) in diagnostic and image-guided procedures. The design addresses shortcomings of existing phantoms by incorporating criteria satisfied by no other single phantom: (1) inserts are fully 3D--spherically symmetric rather than cylindrical; (2) modules are quantitative, presenting objects of known size and contrast for quality assurance and image quality investigation; (3) features are incorporated in ideal and semi-realistic (anthropomorphic) contexts; and (4) the phantom allows devices to be inserted and manipulated in an accessible module (right lung). The phantom consists of five primary modules: (1) head, featuring contrast-detail spheres approximate to brain lesions; (2) left lung, featuring contrast-detail spheres approximate to lung modules; (3) right lung, an accessible hull in which devices may be placed and manipulated; (4) liver, featuring contrast-detail spheres approximate to metastases; and (5) abdomen/pelvis, featuring simulated kidneys, colon, rectum, bladder, and prostate. The phantom represents a two-fold evolution in design philosophy--from 2D (cylindrically symmetric) to fully 3D, and from exclusively qualitative or quantitative to a design accommodating quantitative study within an anatomical context. It has proven a valuable tool in investigations throughout our institution, including low-dose CT, dual-energy radiography, and cone-beam CT for image-guided radiation therapy and surgery.

Evaluation of sparse-view reconstruction from flat-panel-detector cone-beam CT

“…Although the spatial structure of the cylindrical phantom is relatively simple, different contrast levels offered by different inserts provide an opportunity to evaluate reconstruction contrast and spatial resolution. The anthropomorphic head phantom was designed for realistically simulating human head [27], it features not only a natural human skeleton but also contrast-detail spheres approximating soft tissues. These fine and low-contrast structures pose challenges for tasks of image reconstruction from reduced numbers of projections and provide opportunities for evaluating algorithm performance.…”

Geometric calibration of a mobile C‐arm for intraoperative cone‐beam CT

“…FWHM was analyzed from a 2D gaussian fit to axial images of the wire, taking the average of the FWHM in the x and y directions as the reported value, unless otherwise specifically noted. CBCT image quality was assessed in reconstructions of an anthropomorphic head phantom 30 containing soft-tissue simulating contrast-detail spheres ͑11-103 HU; 1.6-12.7 mm diameter͒ and a natural human skeleton. Figures 1͑b͒-1͑e͒ illustrate CBCT image quality in coronal, sagittal, axial, and volume renderings from a full FOV 3D reconstruction of the head phantom using the geometric calibration method.…”

Investigation of lung nodule detectability in low‐dose 320‐slice computed tomography

“…3 The study reported here investigates the lowdose limits of lung nodule detectability in volume CT and identifies optimal low-dose reconstruction techniques particularly with regard to body habitus ranging from average to obese. A volume CT scanner and anthropomorphic phantom 7 form the basis of the study. The experimental variables include factors related to imaging dose ͑kVp and mAs͒ and image reconstruction ͑slice thickness and reconstruction filter͒, and low-dose detectability limits are identified by means of multiple-alternative forced-choice ͑MAFC͒ human observer tests.…”