[Intl_DxMedPhys] EXT MSG Re: [EXTERNAL] Re: ACR CT Pediatric Clinical Image Question

[Szczykutowicz, Timothy P]

to keep dose fixed with size will result in much more noise (lower IQ) with patient size compared to even the weakest AEC curves I am aware from Philips/siemens/(newer GE) who give non constant noise options for AEC curves. See this fig from my book, HVL for tissue is like 19 cm  (ln2/0.0367 from aapm 220 from figure 4 of aapm 204) for constant dose and 3.6 for constant noise, in other words your output will only go up 2x to keep dose constant every 19 cm whereas it needs to go up 2x every 3.6 cm to keep IQ constant. The arguments about largest patients and interstitial fat don’t hold water… bigger pts also get larger voxels which will decrease noise and some vendors apply anti aliasing smoothing with rfov increases as well. But for this chain, with peds, I don’t think I would want to keep dose constant via ssde across size. This is another reason why peds imaging can be tricky, we do want really fast scan times, but the output from the tube (or tubes) for the high pitch 80 cm GE and Canon or the dual source high pitch Siemens isn’t enough at low kV to span all peds pt sizes for routine indications- maybe for chest pectus or something like that.

-stick

[cid:image001.png at 01DBA3C6.8C7D0FE0]

Timothy P. Szczykutowicz, Ph.D., DABR
Associate Professor
Departments of Radiology, Medical Physics and BME
University of Wisconsin Madison
Cell# 1-716-560-7751<tel:(716)%20560-7751>
Office# 1-608-263-5729
he/him/his

From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces+tszczykutowicz=uwhealth.org at lists.osu.edu> On Behalf Of Dave Jordan via Intl_dxmedphys_wd_osu_list
Sent: Tuesday, April 1, 2025 5:56 PM
To: Douglas Pfeiffer <xraydoug at me.com>; Timmerman,Michael <Michael.Timmerman at sanfordhealth.org>; Gauntt, David <davidgauntt at uabmc.edu>
Cc: DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: Re: [Intl_DxMedPhys] EXT MSG Re: [EXTERNAL] Re: ACR CT Pediatric Clinical Image Question


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Mike, I think a reasonable way to make an argument that CTDIvol values are (or are not) reasonable across patient sizes is to compare their SSDE values. If you convert your 10 mGy @ 40-50 lb. to an SSDE, and then also look at the SSDE for the
Mike, I think a reasonable way to make an argument that CTDIvol values are (or are not) reasonable across patient sizes is to compare their SSDE values. If you convert your 10 mGy @ 40-50 lb. to an SSDE, and then also look at the SSDE for the 175 lb. patient, how similar (or not) are they?

Of course there is no rule that SSDE should be constant across patient sizes, but this is still a useful check to see how they compare.

There are some publications that propose useful ways to use patient weight as a size parameter for SSDE instead of patient/effective/water-equivalent diameter, which you need if you’re trying to set up weight-based protocols, although if you have access to the images that were already scanned (sounds like you do) then you should be able to directly measure one of the size parameters used in AAPM Report 204/220.

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