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

Thu Mar 20 11:22:07 EDT 2025

Kai,
            That is a very good question. Not only does radiation dose matter, but iodine contrast dose matters. The reality is coronary CTA is performed for more and more patients. The heart irregularity occurs more frequently. As Mathew suggested, watching the ECG from the CACs scan is helpful. However, the ECG may change or involuntary motion can occur after the contrast injection. PAC or PVC can occur during the scan. In fact, breath motion is major concern. In these cases, prospective gating may not work. A repeat may be the only option. The advantage of prospective gating is no longer there.
The unpredictability of the patient condition makes the task challenging. In our experience, effective instructions to patients before the coronary CTA can be of great help. If prospective gating as a default protocol benefits most of the patients, it may still be the way to go. It may not be adequate for some patients, such as those who’s BMI is 35+. Some vendors have smart gating algorithms, but I am not sure how reliable they are.

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 Yang, Kai, PhD via Intl_dxmedphys_wd_osu_list
Sent: Thursday, March 20, 2025 6:02 AM
To: Matthew Hoerner <mrh5038 at gmail.com>; Szczykutowicz, Timothy P <TSzczykutowicz at uwhealth.org>
Cc: 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

Thank you everyone for sharing your expert knowledge. I really learned a lot. Now I have a related naive question, if the heart rate irregularity affects the dose and quality of the prospective scan, to some extent that not even able to provide

Thank you everyone for sharing your expert knowledge. I really learned a lot. Now I have a related naive question, if the heart rate irregularity affects the dose and quality of the prospective scan, to some extent that not even able to provide
Thank you everyone for sharing your expert knowledge. I really learned a lot.

Now I have a related naive question, if the heart rate irregularity affects the dose and quality of the prospective scan, to some extent that not even able to provide sufficient image quality and requires rescan, what about to go with retrospective at the beginning? Is there any guidelines or rule of thumb when to use retrospective?

Kai

---------------------------------------------------------------------------------------------------------
Kai Yang, PhD, DABR, FAAPM

Medical Physicist, Department of Radiology
Massachusetts General Hospital
Assistant Professor of Radiology
Harvard Medical School

241-C, Suite 200
175 Charles River Plaza
Boston, MA 02114

Email: kyang11 at mgh.harvard.edu
Phone: (617) 724-7169
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From: Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu<mailto:intl_dxmedphys_wd_osu_list-bounces at lists.osu.edu>> On Behalf Of Matthew Hoerner via Intl_dxmedphys_wd_osu_list
Sent: Wednesday, March 19, 2025 9:01 PM
To: Szczykutowicz, Timothy P <TSzczykutowicz at uwhealth.org<mailto:TSzczykutowicz at uwhealth.org>>
Cc: intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto: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

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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
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<mailto: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<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<mailto: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<mailto:yuezhang1984 at gmail.com>>; intl_dxmedphys_wd_osu_list at lists.osu.edu<mailto: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

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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<mailto: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
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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?

[cid:image001.jpg at 01DB996C.7571C6B0]

[cid:image002.jpg at 01DB996C.7571C6B0]

[cid:image003.jpg at 01DB996C.7571C6B0]

[cid:image004.jpg at 01DB996C.7571C6B0]

[cid:image005.jpg at 01DB996C.7571C6B0]

[cid:image006.jpg at 01DB996C.7571C6B0]
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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