# OPTBSV, Ophthalmic Tomography B-scan Volume Analysis. OPTENF, Ophthalmic Tomography 1.2.840.10008.5.1.4.1.1.78.8, Intraocular Lens Calculations Storage (0018,9346), CTDI Phantom Type Code Sequence, SQ, 1. (0018,9351)

CTDIvol is a quantity that can be measured on either a large (32 cm diameter) or The computation of effective dose is performed by estimating organ absorbed

CTDIvol (or CTDI volume) represents the dose for a specific scan protocol which takes into account gaps and overlaps between the radiation dose profile from consecutive rotations of the x-ray source. Therefore CTDIw represents the average radiation dose over the x and y direction whereas CTDIvol CT Dose Index Volume (CTDIvol) The CTDIvol can be calculated as: CTDIvol = [ (N x T)/I] x CTDIw where CTDIw = weighted or average CTDI given across the field of view N = number of simultaneous axial scans er x-ray source rotation T = thickness of one axial scan (mm) I = table increment per axial scan (mm) CTDI vol: (mGy) Is a measurement of “dose” to a large plastic phantom, and for normal size patients CTDI vol underestimates their dose. Should not be considered as the “patient dose” Uses two reference phantoms, 16 cm and 32 cm, depending on scan protocol. The 16 cm reference phantom is used for all The CTDI vol is defined as the CTDI w divided by pitch.

increased CTDI vol leads to an increase in SSDE. From figures 2a and 2b, it seems that the correlation between diameters (D eff and D W) and CTDI vol is stronger (with R2 about 0.8) than the correlation between diameters (D eff and D W) and SSDE (with R2 about 0.5). This is due to the calculation of CTDI vol If CTDI vol is available for each CT examination, organ doses can be calculated using equation 1; for equation 1, the CTDI vol is multiplied to the dose conversion coefficients derived in the previous step. However, if CTDI vol is not available, the value must be reconstructed using equation 2. 321 Anam et al.: Calculation of water-equivalent diameter 321 Journal of Applied Clinical Medical Physics, Vol. 17, No. 4, 2016. of the CT Dose Index (CTDI) and dose-length product (DLP).(10,11) CTDI values are widely used for quality assurance (12) and accreditation purposes.(13) However, CTDI … where both CTDI w and CTDI vol are referenced to a CTDI phantom, and each D L (0), CTDI ∞ and H(L) is dependent on the patient size.

OBJECTIVE.

## CTDI CTDI vol p ( . )= w 36 So CTDI vol is the pitch-corrected CTDI w. Apart from the integration length, which is limited to 100 mm, CTDI vol is practically identical to MSAD based on CTDI w (i.e. MSAD w). Since averaging includes both the cross section and the scan length, CTDI vol therefore represents the average dose for a given scan volume

Currently, the descriptor for estimating patient dose is the size-specific dose Objective. The dosimetric calculations in CT examinations are currently based on two quantities: the volume weighted CT dose index (CTDIvol) and the scan mode, and that doses for helical scan modes are calculated from the axial Thus, CTDIvol estimates the average radiation dose within the irradiated Such measurements of CTDI in the standard head or body CT dosimetry phantom may Monitoring of DLP provides control on the volume of irradiation and overall exposure for For types of scanner not included amongst these calculations DLP is derived from CTDIvol, but incorporates a scan length Can CTDIvol and DLP results tell me two different things? The CTDIvol can be calculated as:.

### Computed Tomography Dose Index (CTDI vol), in mGy according to IEC 60601-2-44, Ed.2.1 (Clause 29.1.103.4), The Volume CTDI vol.It describes the average dose for this image for the selected CT conditions of operation.

–CTDI vol.x Scan Length (units = mGycm).

From figures 2a and 2b, it seems that the correlation between diameters (D eff and D W) and CTDI vol is stronger (with R2 about 0.8) than the correlation between diameters (D eff and D W) and SSDE (with R2 about 0.5).

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CTDI vol is conceptually similar to the MSAD but is standardized with respect to the integration limits (±50 mm) and the factor used to convert the exposure or air kerma measurement to dose in air. For most standard scanning protocols, CTDIw is in the range 10–40 mGy (Table 7.3).

2/3 CTDI 100 (periphery) + 1/3 CTDI 100 (center) CTDI vol (mGy) is obtained by dividing CTDI w by pitch factor.

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### 14 Dec 2018 Thus, the SSDE value can be calculated using the head or body CTDIvol bases with corresponding k value. Keywords: CTDIvol;SSDE

Finally, each CT image header may contain a specific attribute tag for CTDI vol (0018,9345). The Attribute Description is given as “Computed Tomography Dose Index (CTDI vol), in mGy according to IEC 60601-2-44, Ed.2.1 (Clause 29.1.103.4), The Volume CTDI vol. It describes the average dose for this image for the selected CT conditions of CTDI (or CTDI vol), however, is not patient dose.

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### The next step is to use the pitch value (spiral/helical scanning) to calculate the volume CTDI. This is often calculated and displayed by the scanner as part of the

4 Typical CTDI values SAMPLE CALCULATION: PRESCAN A. Determine size of patient 1. AP Projection Scan: 16.8 cm B. 16 cm CTDI phantom used by scanner to calculate CTDIvol C. Displayed CTDIvol = 9.29 mGy D. 9.29 mGy x 1.08 = 10 mGy SSDE Adapted from TG 204. 3/18/2013 20 TG 204 R. Dose Reporting by Radiologists The CTDIvol value reported on the scanner for Actual measurement of CTDI vol. In this study, to calculate the SSDE and exposure dose based on the CT examination data, we needed to consider whether or not the displayed CTDI vol should be used in the simulation.

## 8 Feb 2020 The CTDI vol specifies. the radiation intensity used to perform. a specific The CTDI calculation assumes that the radiation decreases linearly

The units are mGy centimeters (mGy cm). The DLP can be used to calculate a rough estimate of the effective dose. There is a relation between CTDIw and CTDIvol. DLP can be calculated by multiplying CTDI x Scan Length.

For most standard scanning protocols, CTDIw is in the range 10–40 mGy (Table 7.3). Dividing CTDIw by pitch (beam pitch in the case of multislice scanners) gives CTDIvol, which is an approximation to the average absorbed dose within the scanned volume.