[Intl_DxMedPhys] Displayed CTDIvol on Toshiba Aquilion 320 slice

Thu Jun 5 16:56:06 EDT 2025

In my experience, vendors will measure the values at the factory and put into look up tables on the scanners. They will often make different measurements for different options a user can select (like even when it seems it should not make sense to do so because the modes are the same dose wise, like if bowtie, beam energy, mAs are constant and the user changes slice thickness, the CTDIvol should not change on a modern scanner). My understanding of this is that they take different measurements for different slice thicknesses the user can prescribe, which may be a hold over from when they did different focal spot control or collimator settings for different slice thicknesses requests (I don’t think they do this anymore as slice thickness is decoupled from acq slice thickness on all modern scans I know). So the small differences you may see reflects some engineer at the factory repeating the same measurements. This is actually one way when I am testing I know I am doing the exact same thing as previous, if the displayed ctdivol matches to the hundredths place.

Your specific issue though I need to understand more. In volume mode, the scan length is multiples of the collimation. If you are in 16 cm mode, you cannot prescribe 80 or 120 mm? The differences between a 80 and 120 and 160 mm collimation would be a few percent (see below). Our wide axial canon will do 40, 80, 120, 140, and 160 mm in volume mode, so that is probably what you saw as well, it was changing collimation on you.

We have 3 of the aquillion type scanners here (2x prism and 1x insight) but I don’t have CTDIvol tables from Canon, only geometric efficiency tables. I pasted a ctdivol table from a wide axial from GE below, for sure we see little changes in efficiency with collimation changes past 40 mm.

>From a canon prism (this isn’t ctivol, it is geometric efficiency but it explains why we see changes in ctdivol to some degree with collimation changes)
[cid:image001.png at 01DBD5F9.BDEBC5C0]
This is a table from ge showing ctdivol for different collimations relative to 40 mm. this seems like what you are seeing.

[cid:image002.png at 01DBD5F9.BDEBC5C0]

-stick

Timothy P. Szczykutowicz, Ph.D., DABR
Associate Professor
Departments of Radiology, Medical Physics and BME
University of Wisconsin Madison
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From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu> On Behalf Of Dylan DeAngelis via Intl_dxmedphys_wd_osu_list
Sent: Thursday, June 5, 2025 8:34 AM
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Subject: [Intl_DxMedPhys] Displayed CTDIvol on Toshiba Aquilion 320 slice

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Good morning, ACR-testing a Toshiba Aquilion 320 slice CT scanner, for a pediatric head “Volume” protocol with 0. 5 x 320 configuration, we noticed that the displayed CTDIvol was changing based on the scan length (all other parameters
Good morning,

ACR-testing a Toshiba Aquilion 320 slice CT scanner, for a pediatric head “Volume” protocol with 0.5 x 320 configuration, we noticed that the displayed CTDIvol was changing based on the scan length (all other parameters kept the same). Going from 80 to 100 to 120 mm would change the CTDIvol by a few percent.

Is this typical? Does anyone have a solid explanation as to why it would happen? I understand that the “Volume” scan, being so wide, has some cone-beam properties, but I only think of this as having an affect on IQ. Does it also have an affect on the system’s calculation of CTDIvol?

Apologies if this has been discussed before. I’m not very savvy with the ListServ search options.

Thank you,

Dylan DeAngelis, MS, DABR
NYS Licensed Medical Physicist
(Diagnostic Radiological Physics and Medical Nuclear Physics)

Upstate Medical Physics – Diagnostic Radiology, Medical Nuclear & Medical Health Physics, P.C.
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