Opportunistic CT: Difference between revisions
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*<b>Converting</b> between mGy-cm to effective dose (as described by the American Association of Physicists in Medicine (AAPM) Report No. 96): | *<b>Converting</b> between mGy-cm to effective dose (as described by the American Association of Physicists in Medicine (AAPM) Report No. 96): | ||
E ( | E (mSV)=k × DLP | ||
where <code>k</code> is the normalized effective dose per dose-length product for adults. | where <code>k</code> is the normalized effective dose per dose-length product for adults. | ||
*<b>Estimated effective dose</b> for ARTININ (as according to DLP): | |||
E ("mSv" )=0.015 × 400 | |||
E ("mSv" )=6 mSv | |||
Revision as of 00:18, 2 March 2025
Radiation Dose
X-rays are a form of energy – like light and radio waves. X-rays are also called radiation. Unlike light waves, x-rays have enough energy to pass through your body. As the radiation moves through your body, it passes through bones, tissues, and organs differently. This allows a radiologist to create images of them. The radiologist is a specially trained doctor who can examine these images on a computer display. X-rays allow the radiologist to see the structures in your body in very fine detail.
Dose Length Product
Dose length product (DLP) is a measure of CT tube radiation output/exposure (measured in mGy.cm). It is related to volume CT dose index (CTDIvol), but CTDIvol represents the dose through a slice of an appropriate phantom. The dose length product accounts for the length of radiation output along the z-axis (the long axis of the patient). It may be described by the following equation:
DLP = (CTDIvol in mGy) . (length of scan in cm)
The dose length product does not take the size of the patient into account and is not a measure of absorbed dose. If the AP and lateral dimensions of the patient are available, then the size specific dose estimate (SSDE) can be used to estimate the absorbed dose.
Effective Dose
Some estimates of effective dose are summarized in the table below, taken from the cited sources.
| Scan | Effective Dose (mSv) |
|---|---|
| Head | 2.2 |
| Full Spine | 20.6 |
| Cervical | 3.6 |
| Thoracic | 12.0 |
| Lumbar | 5.0 |
| Chest | 6.0 |
| Chest/Abdo/Pelvis | 19.0 |
| Abdo/Pelvis | 15.6 |
| Knees | 0.16 |
| Ankles | 0.14 |
1Conference of Radiation Control Program Directors (CRCPD) Nationwide Evaluation of X-ray Trends (NEXT) 2005-2006 report (https://crcpd.org/document/nationwide-evaluation-of-x-ray-trends-next-tabulation-and-graphical-summary-of-the-2005-2006-survey-of-computed-tomography/)
2CRCPD, Publication E-07-2, Tabulation and Graphical Summary of 2000 Survey of Computed Tomograph, (NEXT), August, 2007
3Biswas et al. Radiation Exposure from Musculoskeletal Computerized Tomographic Scans. The Journal of Bone and Joint Surgery, 2009.
Notes:
- Full Spine: From the base of the skull (C1) to the sacrum (through L5), effective dose of 20.6 mSv (adding up dose of all spine scans)
- Extended Chest/Abdo/Pelvis (or Full Spine + Abdo/Pelvis): from the base of the skull (C1) through the proximal femur. Effective dose of 25.2 mSv (cervical spine + chest + abdo/pelvis). Likely this is an overestimation.
- Dose Length Product (DLP) of ARTININ scans: usually between 270 – 400 mGy-cm
- Converting between mGy-cm to effective dose (as described by the American Association of Physicists in Medicine (AAPM) Report No. 96):
E (mSV)=k × DLP
where k is the normalized effective dose per dose-length product for adults.
- Estimated effective dose for ARTININ (as according to DLP):
E ("mSv" )=0.015 × 400
E ("mSv" )=6 mSv
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Calibration
Do some more stuff about calibration.