A semianalytic model to investigate the potential applications of x-ray scatter imaging

• Published in: Medical physics (Lancaster) 1998-06, Vol.25 (6), p.1008-1020
• Main Authors: Leclair, Robert J., Johns, Paul C.
• Format: Article
• Language: English
• Subjects: 87.56.01; Biophysical Phenomena; Biophysics; blood; bone; brain; diagnostic radiography; Electron, neutron and x‐ray diffraction and scattering; General theory and mathematical aspects; Humans; Image analysis; liver; Mathematics; Medical image noise; Medical imaging; Medical X‐ray imaging; Models, Theoretical; muscle; Muscles; Organ Specificity; Phantoms, Imaging; Photons; physiological models; Radiographic Image Enhancement - methods; Radiography; Scattering, Radiation; Technology, Radiologic; Water; X-Rays; X‐ray imaging; x‐ray scatter imaging, coherent scatter, contrast, signal‐to‐noise ratio (SNR), numerical analysis; X‐ray scattering
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.598279

Although x-ray scatter is generally regarded as a nuisance that reduces radiographic contrast (C) and the signal-to-noise ratio (SNR) in conventional images, many technologies have been devised to extract useful information from the scattered x rays. A systematic approach, however, for analyzing the potential applications of x-ray scatter imaging has been lacking. Therefore, we have formulated a simple but useful semianalytic model to investigate C and SNR in scatter images. Our model considers the imaging of a target object against a background material of the same dimensions when both are situated within a water phantom. We have selected biological materials (liver, fat, bone, muscle, blood, and brain matter) for which intermolecular form factors for coherent scattering were available. Analytic relationships between C and SNR were derived, and evaluated numerically as the target object thickness (0.01–40 mm) and photon energy (10–200 keV) were systematically varied. The fundamental limits of scatter imaging were assessed via calculations that assumed that all first-order scatter exiting the phantom, over 4π steradians, formed the signal. Calculations for a restricted detector solid angle were then performed. For the task of imaging white brain matter versus blood in a 15 cm thick water phantom, the maximum SNR, over all energies, for images based on the detection of all forward scatter within the angular range 2°–12° is greater than that of primary images for target object thicknesses ⩽23  mm . Use of the backscattered x rays within the range 158°–178° to image objects 3 cm below the surface of a 25 cm thick water phantom allows the liver to be distinguished from fat with a SNR superior to that of primary imaging when the objects are ⩽22  mm thick. Our analysis confirms the usefulness of scattered x rays, and provides simple methods for determining the regimes of medical interest in which x-ray scatter imaging could outperform conventional imaging.