P+® X-ray QA Test Phantom
“X-ray equipment should be routinely checked for optimal imaging performance and appropriate radiation dose. The P+® X-ray QA Test Phantom is a quality assurance and control instrument ideal for use by physicians and X-ray technicians to ensure superior radio graphic quality and patient safety.”
“P+© is simple to use and gives me confidence in knowing that my equipment is working properly before I image my patients. “ Carol Barnhardt RT(R)(M)(CT) Novant Health Milestone Family Medicine, Salisbury, NC.
“Thanks for letting us try out your phantom. I think it is most useful the way you have it advertised” Bob Clark (Medical Physicist, Washington State Radiation Control Section)
“Surveyors will be asking questions and having dialogue with the leaders about their approach to improving safety and making patients safe when they’re having radiation-related diagnostic tests and treatments”. What matters is that the facilities “are thinking, are approaching, and are putting in place a plan”. Pujols-McKee, Joint Commission on Accreditation of Hospitals Organization (Sentinel Alert, August 2016)
“The objective is to get patient exposures below the 3rd NEXT quartile instead of above it and to maintain image quality appropriate to the exams.” www.crcpd.org/NEXT
“The objective is to demonstrate where patient exposures are relative to others in the medical imaging community”. www.crcpd.org/NEXT
“The company supplying new digital imaging equipment should supply information on the recommended exposures which give diagnostic images with the lowest possible patient dose. Patient dose should be proved with an in-beam phantom.” http://www.mhra.gov.uk/Safetyinformation
“North Carolina does not have specific QC rules in place except the federal ones that apply to mammography. Because we do not approve or endorse a product does not prevent you from marketing such a device in N.C, We wish you the best in your endeavors.” Jenny Rollins, Radiology Compliance Branch Manager, NC Department of Health and Human Services Radiation Protection Section
A Federal Standard is needed that applies equally to film-screen and digital imaging with respect to image resolution and radiation dose. It is simple to understand, requires little additional training, and is non-burdensome.
By: Steve R. Arey, Certified Radiological Equipment SpecialistGeneral practitioners, Chiropractors and hospitals across America are replacing their x-ray film processors with CR & DR Digital Imagers. It is found that many physicians are not aware of a loss in image resolution after the change.
“There are no regulations for digital, only for film screen mammography (21CFR 900.12(e))” says the FDA Office of Consumer Safety.
“It is our understanding that, in general, digital systems may provide a lower overall system resolution than film-screen systems, but one that the radiographic community has considered adequate for the diagnostic purposes of the systems. Such variation might be more noticeable in those systems where digital imaging capability is added as an “upgrade” to general purpose systems than in those systems that are specifically designed to function as digital systems.” 1
The National Evaluation of X-ray Trends survey publishes radiation dose and resolution details for typical exams performed regularly in the nation. Among those exams surveyed is the Adult 23cm AP Abdomen exam. NEXT (2006) survey results for the 23cm AP Abdomen exam show that the average radiographic technique is 76kVp and 67mAs. The mean radiation dose for this exam was 3.2 mGy or (326mR) in 1995 and 3.4 mGy (344mR) in 2006. 2
Is this average radiation dose acceptable? Are the doses which are two and three times higher than average acceptable? Does the radiographic community know the difference? Has image quality increased with the increase in radiation dose to the general public?
In 2006, Americans were exposed to more than seven times as much ionizing radiation from medical procedures as was the case in the early 1980s. 3
Medical radiation was placed on the known list of causes of cancer in November 2007. 4
Ionizing radiation can indirectly result in cancer in cells beyond those that are directly irradiated. The findings suggest that current estimates of cancer risks from ionizing radiation exposure may be too low. 5
These facts create a valid reason to implement a Standard for image quality and radiation dose which will apply to existing imaging systems (film-screen) as well as upgraded imaging systems (CR digital) now and in the future.
A relationship exists between new (digital) and old (film-screen) imaging.A two armed study is performed measuring the image quality relationship between the traditional method of sensitometry for film-screen imaging, which is the control group, and the study arm which is the phantom visual image method.6
The purpose of this study is to show data supporting the hypothesis that a phantom visual image adequately displays image details which are within the control ranges of sensitometry in medical x-ray film developing.
A phantom is manufactured from commercially available 6 inch diameter HDPE material having a specific gravity of .97. The amount of HDPE material used to make a phantom is the thickness that creates a radiographic image on a processed film the same density as 23 cm of water. Two halves of the HDPE material completes an assembly having milled recesses to accommodate five (5) screens of wire mesh ranging in weave of 20,40,50,60 and 80 meshes in lines per inch. Sixteen holes, (4 groups of 4 holes) 1mm,2mm,4mm and 8mm are milled to depths of 1mm,2mm,4mm and 8mm. When assembled, these detail resolution objects are within the center of the phantom. Mesh screens are positioned on a 45ο angle with respect to the phantom centerline to reduce grid line interference. The two halves are assembled with screws.
Fifty (50) exposures, using the same technique and measuring radiation dose for each exposure, are recorded on 14 x 17 films. Collimation and lead shielding are used to prevent exposure of the film outside of the phantom image area. The latent images are placed back into the box in the darkroom and transported to a darkroom laboratory where the film processor is set up under controlled working conditions.
An H&D curve is created, control points selected and sensitometric charting midlines produced for base fog, speed, and contrast. Temperature measuring and chemical replenishment measuring is performed without removing the processor covers. Measurements are controlled and exacting.
A sensitometric step wedge is flashed on two opposite edges of a test film containing the latent phantom image and processed. The processed films with sensitometric steps and phantom image are averaged and plotted on the control charts. The phantom visual resolution objects from the test film are visually identified and plotted.
It is found with changes in film processing factors (i.e.: developer temperature, specific gravity, replenishment rates and contamination of developer with fixer) that phantom image details are lost visually within the control ranges of sensitometry. 6
The Need for a StandardIn the field it is found that several CR digital systems are unable to resolve 40 lines per inch in the phantom image. 20 mesh in lines per inch is equivalent to .8 lp/mm, 40 mesh= 1.6 lp/mm, 50 = 1.97 lp/mm, 60 = 2.36 lp/mm, 80 = 3.15 lp/mm. There are no federal regulations specifying image resolution for either general diagnostic film-screen or digital imaging. There are no federal regulations specifying how resolution should be measured. In the field it is also found that the techniques selected using CR digital imaging must be increased above those used for film-screen imaging to obtain an acceptable background density of the phantom on the computer monitor. With CR digital as many as eight to twelve of the sixteen holes in the phantom image can be visualized. 7
In the field, film-screen images of the phantom are found on average to resolve 50 mesh or better and 13 or more out of 16 holes. A daily plotting chart is used to document this image testing.8
Hospitals and physicians send images via electronic media to be interpreted on consultants imaging devices. A phantom image created at the source imaging system should be included with patient images which are sent to consultants. The consulting physician should be able to resolve a minimum number of lines and holes in the phantom image on their own monitors.
A Simple SolutionIf a general diagnostic facility technologist were to radiograph a Standard phantom representing the Adult 23cm Abdomen exam each day prior to exposing patients, a very simple quality concept is realized through “readiness testing”. Charting of this daily method translates directly a simple 1 minute visual test method that applies equally to either film-screen or digital.
In practice, a radiologic technologist with a test phantom, which represents the 23cm Abdomen exam, would select the least dose technique which produces the best image of the phantom that the clinic equipment is capable of. This technique is recorded and that same technique is used to x-ray the phantom daily and the image processed. Phantom images are viewed daily on an x-ray view box or video monitor prior to exposing patients to ionizing radiation. Acceptable radiation dose for the phantom image should be a Standard. The radiation dose of an individual clinic’s phantom can be measured by a service company, medical physicist or state surveyor to see if the clinic’s equipment is relative to the National Standard for the 23 cm AP Abdomen exam. Minimum image resolution should be a Standard. Any systems that can’t meet the Standard need to be corrected or are not allowed.
In 1996 when MQSA Standards were implemented, mammography machines that did not meet the minimum focal spot requirement of the new Standard were not allowed to be used.
The MHRA (a European FDA) has published recommendations regarding digital radiography systems.
(1) The company supplying new digital equipment should supply information on the recommended receptor exposures, which give diagnostic images with the lowest possible patient dose for each particular examination.
(2) This figure for the patient dose should be proved with an in-beam phantom during hand-over; the manufacturer should also specify the phantom parmeters.9
- Daily phantom imaging does not replace the need for annual calibration of the imaging system by a qualified and registered service individual or medical physicist.
- Regulations should encompass both new and old equipment.
- Regulations should be simple to comply with and easy to understand.
- Testing should be done daily to insure systems maintain a minimum level of image quality.
- Testing should be done daily to insure systems meet an acceptable level of radiation dose.
- Image quality should be determined by reference to a National Standard not by individual imaging equipment manufacturers.
- Students of any discipline learn and retain knowledge most successfully if they see a meaningful relationship between the subject matter and their daily life. With little training, a phantom image is just like taking another x-ray.
REFERENCES1. Center for Devices and Radiological Health; Office of Communication, Education, and Radiation Programs; Division of Mammography Quality and Radiation Programs; Diagnostic Devices Branch; Consumer Safety Officer, Tom L. Mosely. firstname.lastname@example.org
2. NEXT; National Evaluation of X-ray Trends; http://www.crcpd.org – Medical Radiation, NEXT
3. NCRP; National Council on Radiation Protection, Report No. 160 Press Release March 3, 2009 http://www.ncrp.gov
4. National Toxicology Program; 11th Report to Congress 2007; http://www.ntp.niehs.nih.gov
5. Joan Stephenson, PhD. X-ray collateral Damage?; Vol.300 No.11, September 17, 2008; JAMA
6. “Comparing the Phantom Imaging Method to the Sensitometric Method for Quality Control in the film processor”; 102nd North Carolina Academy of Science; Catawba College Department of Chemistry; Kendall Prescott, 1st Place Derieux Award, 2005. http://www.catawba.edu – Catawba College students make News – March 18-20, 2005
7. CR Digital plotting chart – http://wwwxrayqa.com P+ X-ray Phantom, CR Digital plotting chart
8. Film-Screen plotting chart – http://www.xrayqa.com P+ X-ray Phantom, Film-Screen plotting chart
9. MHRA, Medicines and Healthcare products Regulatory Agency: Radiation dose issues in digital radiography systems; http://mhra.gov.uk – General Safety Information and Advice/ Technical Information/Radiation Dose Issues in digital radiography systems
“Another fact that has remained clear is the critical role that radiographers play in ensuring patient radiation safety during medical imaging procedures. Radiographer must adhere to the “as low as reasonably achievable” (ALARA) principle by keeping radiation dose as low as is reasonably achievable when performing digital radiography.” Best Practices in Digital Radiography https://www.asrt.org/docs/default-source/publications/whitepapers/asrt12_bstpracdigradwhp_final.pdf