Measurement of focal spot size with slit camera using computed radiography and flat-panel based digital detectors

• Published in: Medical physics (Lancaster) 2003-07, Vol.30 (7), p.1768-1775
• Main Authors: Rong, Xiujiang J., Krugh, Kerry T., Shepard, S. Jeff, Geiser, William R.
• Format: Article
• Language: English
• Subjects: biomedical equipment; biomedical measurement; Calibration - standards; cameras; computed radiography; diagnostic radiography; digital imaging; Equipment Failure Analysis - instrumentation; Equipment Failure Analysis - methods; Equipment Failure Analysis - standards; Film Dosimetry - instrumentation; Film Dosimetry - methods; flat‐panel; focal spot size; Image sensors; Medical imaging; Medical X‐ray imaging; Non‐ionizing radiation equipment and techniques; Radiographic Image Enhancement - methods; Radiographic Image Enhancement - standards; Radiography; Radiometry - instrumentation; Radiometry - methods; Radiometry - standards; Reproducibility of Results; Sensitivity and Specificity; slit camera; Time measurement; Tomography, X-Ray Computed - instrumentation; Tomography, X-Ray Computed - methods; Transducers; United States; Vacuum tubes; X-Ray Intensifying Screens; X‐ and γ‐ray sources, mirrors, gratings, and detectors; X‐ray detection; X‐ray detectors; X‐ray imaging; x‐ray tube
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1579583

The purpose of this study was to evaluate the use of digital x-ray imaging detectors for the measurement of diagnostic x-ray tube focal spot size using a slit camera. Slit camera images of two focal spots for a radiographic x-ray tube were acquired with direct-exposure film (DF) (as specified by the National Electrical Manufacturers Association [NEMA] Standards Publication No. XR 5, 1992), computed radiography (CR) imaging plates, and an a-Si:H/CsI:Tl-based flat-panel (FP) detector. Images obtained with the CR and the FP were acquired over a broad range of detector entrance exposure levels. The DF slit images were evaluated according to NEMA specifications (visually, using a 7× magnifying glass with reticule) by six medical physicists. Additionally, the DF images were digitized and the focal spot sizes obtained from the digital profiles of the slit. The CR and the FP images were analyzed in a manner similar to the digitized DF images. It took less than 20 minutes for a complete CR or FP measurement of focal spot size in two dimensions. In comparison, a typical DF measurement with visual evaluation takes at least 60 minutes, in our experience. In addition to a great reduction in measurement time achieved by using digital detectors, the tube loading requirements were reduced to ∼20 mAs compared with ∼1000 mAs when using the DF technique. The calculated focal spot sizes for CR and FP differed from those of digitized DF by −2.4% to +4.8% (σ=2.5%), far less than the −16.6% to +9.3% (σ=8.1%) variability introduced by the visual evaluation of the slit image. In addition, the calculated focal spot sizes for the CR and the FP images maintained a coefficient of variation