Definition/IntroductionImage quality can be defined as the attribute of the image that influences the clinician's certainty to perceive the appropriate diagnostic features from the image visually.[1][2] Quality assurance or quality improvement is defined as the proactive actions to enhance the quality of care and services and cost-effectively remove the waste. In this article, we will discuss the fundamental concepts of digital radiographic image quality assurance. The most common digital radiographic detectors are computed radiography (CR) and digital radiography (DR). The important components of the radiographic image quality include contrast, dynamic range, spatial resolution, noise, and artifacts.[3] We will discuss these components briefly. Show
Issues of ConcernFactors affecting image quality.
Clinical SignificanceBy adjusting kVp, decreasing mAs, and decreasing focal spot size, one can obtain high-quality digital radiographs with a lower radiation dose. Although a higher radiation dose leads to less noise and better image quality, one should be very cautious about the radiation dose to the patient. The radiographic systems should be optimized to obtain image quality that provides diagnostic accuracy at least possible radiation dose. The selection of radiographic projection affects the radiation dose. For example, in chest radiographs, anterior-posterior (AP) orientation has a higher radiation dose compared to the posterior-anterior (PA) view due to greater radiation exposure of breasts. In pediatric patients, the use of as low as reasonably achievable (ALARA) principle is essential during radiographic studies since children are more susceptible to the effects of ionizing radiation than adults.[7][8] The radiographic detectors with higher DQE provide superior SNR performance that enables radiation dose reduction without significantly affecting image quality, particularly in pediatric patients.[3][6][7] There is a tendency to use more radiation dose in digital imaging to reduce image noise called 'dose creep.'[3] The utilization of a validated chart containing predetermined technical parameters based on the patient size helps avoid dose creep.[3] American Association of Physicists in Medicine Task Group 116 report is a great resource for recommended exposure indicator for digital radiography.[3] The appropriate use of effective collimation and anti-scatter grid reduces the scattered radiation and improves image quality by reducing noise and improvement of SNR. The anti-scatter grid is most useful when the amount of scattered radiation is high, especially if the patient's thickness is greater than 10 cm.[3] However anti-scatter grid is not useful in smaller or pediatric patients or for smaller body part imaging. For the troubleshooting of poor-quality radiographic images, the first step should be adjusting the post-processing parameters to see if the image can be reproduced with better image quality. One should optimize image acquisition and processing protocols to avoid repeat examination of the patients and unnecessary radiation exposure. The optimal imaging protocols should be developed and established with the help of a medical physicist to obtain consistently high image quality at minimum possible radiation dose. The images should be properly compressed for transmission and storage without loss of significant clinical data. The appropriate image post-processing should be used to improve the image display. The imaging systems should comply with appropriate state and federal regulations. The imaging systems should minimize the incidence of poor-quality images and maximize clinical efficiency and continuous quality improvement.[3] A meticulous quality assurance program is essential for consistently maintaining high-quality performance. The image quality should be monitored by doing acceptance testing to assure safety and image quality, periodical checkups and maintenance assessment, and thorough annual inspections under the guidance of the medical physicist.[9] In summary, we discussed important components of the radiographic image quality and various factors affecting image quality. This knowledge is useful to obtain high-quality digital radiographs with the lowest possible radiation dose to improve the clinician's diagnostic accuracy. Review QuestionsReferences1.Rossmann K, Wiley BE. The central problem in the study of radiographic image quality. Radiology. 1970 Jul;96(1):113-8. [PubMed: 5420393] 2.Barrett HH, Yao J, Rolland JP, Myers KJ. Model observers for assessment of image quality. Proc Natl Acad Sci U S A. 1993 Nov 01;90(21):9758-65. [PMC free article: PMC47653] [PubMed: 8234311] 3.Williams MB, Krupinski EA, Strauss KJ, Breeden WK, Rzeszotarski MS, Applegate K, Wyatt M, Bjork S, Seibert JA. Digital radiography image quality: image acquisition. J Am Coll Radiol. 2007 Jun;4(6):371-88. [PubMed: 17544139] 4.McCollough CH. The AAPM/RSNA physics tutorial for residents. X-ray production. Radiographics. 1997 Jul-Aug;17(4):967-84. [PubMed: 9225393] Schueler BA. Clinical applications of basic x-ray physics principles. Radiographics. 1998 May-Jun;18(3):731-44; quiz 729. [PubMed: 9599394] 6.Krupinski EA, Williams MB, Andriole K, Strauss KJ, Applegate K, Wyatt M, Bjork S, Seibert JA., ACR. AAPM. Society for Imaging Informatics in Medicine. Digital radiography image quality: image processing and display. J Am Coll Radiol. 2007 Jun;4(6):389-400. [PubMed: 17544140] 7.Willis CE, Slovis TL. The ALARA concept in pediatric CR and DR: dose reduction in pediatric radiographic exams--a white paper conference. AJR Am J Roentgenol. 2005 Feb;184(2):373-4. [PubMed: 15671348] 8.Eslamy HK, Newman B, Weinberger E. Quality improvement in neonatal digital radiography: implementing the basic quality improvement tools. Semin Ultrasound CT MR. 2014 Dec;35(6):608-26. [PubMed: 25454055] 9.Mahesh M. Essential Role of a Medical Physicist in the Radiology Department. Radiographics. 2018 Oct;38(6):1665-1671. [PubMed: 30303789] Which exposure factor primarily controls radiographic density?Radiographic or Optical Density
In conventional film / screen system, density is controlled by the exposure factors, primarily the mAs. Because exposure darkens the image, an increase in mAs will result in a darker radiograph, while a decrease will cause it to be lighter.
Does mAs or kVp control density?Increasing kVp also contributes to the overall density (darkness) of the image. A fairly small adjustment in kVp can have a significant effect on the image. Just a 15% increase in kVp is roughly equivalent to doubling the mAs.
What is the main controlling factor of density?The density can be defined as the photographic effect producing different degree of blackness on the film measured by light absorption through it. The factor that controls contrast is said to be KV and the factor that controls density is termed as mAs i.e. the product of milliampere and the duration of exposure.
What is the controlling factor for radiographic exposure?Mas is the controlling factor of density and IR exposure and it is affected because as Mas increases, x-ray exposure increases proportionally and film density also increases.
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