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

Wed Mar 19 16:39:05 EDT 2025

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?

[cid:image001.jpg at 01DB98D1.E8757440]

[cid:image002.jpg at 01DB98D1.E8757440]

[cid:image003.jpg at 01DB98D1.E8757440]

[cid:image004.jpg at 01DB98D1.E8757440]

[cid:image005.jpg at 01DB98D1.E8757440]

[cid:image006.jpg at 01DB98D1.E8757440]
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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