[Intl_DxMedPhys] [External] Higher doses (CTDIvol) for Prospective Cardiac scans on Siemens Force CT

Wed Mar 19 21:00:34 EDT 2025

Good evening,

For Axial/sequential scans Siemens reports the beam on time within the R-R
cycle as the rotation time.  So you can see how much padding it added
here, as Troy mentioned prior.  The patient's heart rate averaged 59 beats
per minute so your R-R duty cycle was about 75%.  If you go into the Heart
View table you can see what is prescribed based on the heart rate and
variability.  Usually its 200 ms or 20% at most.  By default Siemens adds a
padding of 150 ms (you can verify this by running a DS_Card_Seq scan using
the dummy pulse and your CTDI chamber in the center hole).  So that would
be a max of 350 ms for this patient or 35% of the R-R cycle.  The Care Dose
curve we use at Yale is very strong as well.  I think that makes sense
because the size of the heart isn't changing much with patient size so you
don't get the higher pixel size with the larger DFOV you may get with other
body parts.

Since you guys are doing calcium scores prior to the Coronary, you could
consider having the techs see if the heart rate is irregular or look for
poor quality EKG waveforms from the calcium score.  Also, your Rads should
be able to put the calcium score in the MPR and plan which sections may
hypothetically get the stairstep artifact to avoid repeats and be more
aggressive in how you use axial vs helical.

I think this case illustrates (and I have many more) why the new eCQM
shouldnt apply to cardiac imaging.  As Troy pointed out, the heart rate,
heart rate variability, and ECG quality play such a major role and there is
no way to correct for that.  Now add on helical where your pitch is
determined by the heart.  And having a low rotation time (with higher
temporal resolution) can "Force" you into a low pitch value which is a
substantial dose penalty and no improvement in image noise.

Matt Hoerner, Yale New Haven Hospital/Yale School of Medicine

On Wed, Mar 19, 2025 at 5:03 PM Szczykutowicz, Timothy P via
Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:

> TI says 0. 8 seconds, that is very long, I am not sure how a FORCE reports
> when it does an extra beat or two if an irregularity is detected, but I bet
> it scanned 1 or more rotations and what you see there is the sum of
> multiple rotations. I would
>
> TI says 0.8 seconds, that is very long, I am not sure how a FORCE reports
> when it does an extra beat or two if an irregularity is detected, but I bet
> it scanned 1 or more rotations and what you see there is the sum of
> multiple rotations.
>
>
>
> I would ask Lior Molvin, he was at Stanford, now at Duke. He is a cardiac
> Siemens super user, gives great talks on this topic. I don’t have his Duke
> email, he is on linkedin.
>
>
>
> Timothy P. Szczykutowicz, Ph.D., DABR
> Associate Professor
> Departments of Radiology, Medical Physics and BME
> University of Wisconsin Madison
> Cell# 1-716-560-7751 <(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 *Zhou, Yifang (Jimmy), Ph.D.
> via Intl_dxmedphys_wd_osu_list
> *Sent:* Wednesday, March 19, 2025 3:39 PM
> *To:* Yue Zhang <yuezhang1984 at gmail.com>;
> intl_dxmedphys_wd_osu_list at lists.osu.edu
> *Subject:* Re: [Intl_DxMedPhys] [External] Higher doses (CTDIvol) for
> Prospective Cardiac scans on Siemens Force CT
>
>
>
> WARNING: This email appears to have originated outside of the UW Health
> email system.
> DO NOT CLICK on links or attachments unless you recognize the sender and
> know the content is safe.
>
> Dear Yue, The highest mA per tube from Siemens is 1,300. 1,935 mA is the
> sum of the mA from both tubes. Therefore, each tube’s mA in the case was
> 1,935/2 = 966 mA. The mAs in the dose report is the mAs per rotation, which
> is related to each
>
> Dear Yue,
>
>   The highest mA per tube from Siemens is 1,300. 1,935 mA is the sum of
> the mA from both tubes. Therefore, each tube’s mA in the case was 1,935/2 =
> 966 mA. The mAs in the dose report is the mAs per rotation, which is
> related to each tube’s mA by a factor of 2.
>
>   In my opinion, the follwoing may be possible reasons for the high dose.
>
>    1. Patient size and modulation strength. For cardiac, the reference
>    patient thickness is 29.4 cm per Siemens. This would make the patient in
>    your case use “very strong” modulation. I would suggest to change the
>    strength either to “strong” or  to “average”. The CACs series used 12.4
>    mGy, which also indicated the strength of “very strong” being used.
>    2. ECG irregularity due to A-fib, PAC, or PVC. It would demand more
>    cardiac cycles.
>    3. Whether the gated window used millisecond from the R-peak or R-R
>    percentage matters. If the latter was used, a slower heart rate could
>    extend the beam-on time. There are different suggestions as where to gate
>    the CT beam. Either at diastole when the heart rate is not high or at
>    systole when the rate is high (>=90 bpm). Some even use systole for all
>    cases with approximately 280 ms to 440 ms after the R-peak.
>
>   Hope this helps.
>
>
>
> Jimmy Zhou
>
> Cedars-Sinai Medical Center
>
>
>
> *From:* Intl_dxmedphys_wd_osu_list <
> intl_dxmedphys_wd_osu_list-bounces+yifang.zhou=cshs.org at lists.osu.edu> *On
> Behalf Of *Yue Zhang via Intl_dxmedphys_wd_osu_list
> *Sent:* Wednesday, March 19, 2025 12:15 PM
> *To:* intl_dxmedphys_wd_osu_list at lists.osu.edu
> *Subject:* [External] [Intl_DxMedPhys] Higher doses (CTDIvol) for
> Prospective Cardiac scans on Siemens Force CT
>
>
>
> Hi List, We are experiencing higher doses (CTDIvol) for Prospective
> Cardiac scans on Siemens Force CT. I am trying to figure out the reason.
> This was a prospective cardiac acquisition (DS_Cor Seq) that exceeded the
> 60 mGy limit, reaching 121.
>
> Hi List, We are experiencing higher doses (CTDIvol) for Prospective
> Cardiac scans on Siemens Force CT. I am trying to figure out the reason.
> This was a prospective cardiac acquisition (DS_Cor Seq) that exceeded the
> 60 mGy limit, reaching 121. 49
>
> Hi List,
>
>
>
> We are experiencing higher doses (CTDIvol) for Prospective Cardiac scans
> on Siemens Force CT. I am trying to figure out the reason.
>
>
>
> This was a prospective cardiac acquisition (DS_Cor Seq) that exceeded the
> 60 mGy limit, reaching 121.49 mGy. Our prospective cardiac scan is done in
> the sequential mode. CarekV is on. The DICOM tag for pitch, (0018, 9311) is
> 0.  Patient Weight = 227 lb. The patient was not very big, from our point
> of view.
>
>
>
> Unfortunately no ECG on PACS, I can't see the exact heart beat pattern.
> But from PACS, Cardiac Series showed 63, 59, 57, 60 bpm, and 1935 mA
> constantly. From the scout, the heart position is a little higher on the
> table. What do you think?
>
>
>
> Why did the scanner choose to use such high mA? The only things I can
> think of that might trick the AEC in a wrong way, are the wires on the
> patient, or the jewelry or metals on the side of cheek (red arrows in the
> 3rd pic). But, can those little things trigger the AEC to choose such high
> mA during the acquisition?
>
>
>
>
>
>
>
>
>
>
>
>
>
> In the above picture, the cardiac CARE Dose curve was changed in June 2023
> from the default average to the current ones. Because the radiologists
> complained about image quality. We don't know how Siemens defines Adult
> slim or obese.
>
>
>
> My question is, what could be the reason to cause such a high dose in
> prospective cardiac scans? Thank you very much.
>
>
>
> --
>
> *Yue*
>
>
>
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