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

Fri Mar 21 09:32:58 EDT 2025

Hi Yue,

The case you’ve listed below shows heart rate with min 61 max 63. The heart rate is regular and low. This would be a perfect candidate for gated flash on Siemens Force. 😊

For your DS_CroSeq, you should check the triggering setting. The scan is 25% dose region and range is 100% range. You want to limit your range if you want to reduce the CTDI. See the screen capture below.

I’ve also included the siemens recommendation for the scan modes for different heart rate and irregularities. Again, please work with your radiologists/cardiologists to optimize your cardiac scan strategy.

e 

From: Yue Zhang <yuezhang1984 at gmail.com> 
Sent: Thursday, March 20, 2025 5:08 PM
To: Troy Zhou <troyxzhou at icloud.com>; yifang.zhou at cshs.org; TSzczykutowicz at uwhealth.org; mrh5038 at gmail.com; Kai Yang PhD <kyang11 at mgh.harvard.edu>; Mark Supanich <Mark_Supanich at rush.edu>
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 very much, Troy, Yifang, Timothy, Matthew, Kai, and Mark. I learned a lot. Unfortunately, the tech didn't send this patient's ECG records to PACS. So I can't verify if this patient had ECG irregularity, or large variation in heart rate.

If we don't have any ECG graph, and we only knew the patient's average heart rate was 60 bpm, can we still calculate or estimate the RR interval? Is the following calculation correct? RR interval = 60 seconds / Heart Rate (bmp) = 60 / 60 = 1 second.

I want to share another example below: another patient who was scanned on another Siemens Force CT, with ECG graphs. It was also a prospective cardiac acquisition (DS_Cor Seq) that exceeded the 60 mGy limit (so it also triggered a Radimetrics CT alert), reaching 101.24 mGy. The prospective cardiac CT protocol should be the exact same for the two patients: in the sequential mode, and CarekV and CareDose is on. The DICOM tag for pitch, (0018, 9311) is 0. Patient Weight = 117.93 kg = 260 lb, which was heavier than the first patient of 227 lb.

The 6th picture was the ECG graph: is there any ECG irregularity? It took 5 cardiac cycles to complete the scan. The X-ray beam fully on time (solid horizontal line) was very long, but only a small portion (rectangle) was used for image recon. Does this mean the majority of X-ray beam fully on time is a waste? What determines the length of the solid line (beam fully on)? Did the patient's slow heart rate result in a longer full X-ray beam-on time? Could half of the solid horizontal line become a dash line (only 20% of X-ray beam on)? What could be the reason to cause such a high dose in this prospective cardiac scan? 

Thank you very much.

On Thu, Mar 20, 2025 at 8:47 AM Troy Zhou 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:

Siemens has their recommendations for which protocols e. g. flash spiral, adaptive cardio sequence or retrospective gated spiral, to use depending on the heart rate and irregularity. You can use it as a starting point to fine tune your protocols

Siemens has their recommendations for which protocols e.g. flash spiral, adaptive cardio sequence or retrospective gated spiral, to use depending on the heart rate and irregularity. You can use it as a starting point to fine tune your protocols to match your radiologist’s preference.

Troy 

On Mar 20, 2025, at 9:06 AM, Yang, Kai, PhD 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:

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:  <https://urldefense.com/v3/__http://kyang11@mgh.harvard.edu__;!!KGKeukY!zVnn-xcloCcJrHjoHnM02sJzK6Yl6w2PDVX_6VKsC924Csh7VUxOh3ZfxKUAmFCvPfr3Zs1chPFoukQqf5Zzxx6P18r25Cf2jKMu3lp2$ > kyang11 at mgh.harvard.edu

Phone: (617) 724-7169  

---------------------------------------------------------------------------------------------------------

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
To: intl_dxmedphys_wd_osu_list at lists.osu.edu <mailto: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?

<image001.jpg>

<image002.jpg>

<image003.jpg>

<image004.jpg>

<image005.jpg>

<image006.jpg>

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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