Thoracic Triple Rule-Out in Low Dose Acquisition Technique Using Prospective ECG Triggering

SOMATOM Definition scanning

Johannes Rixe, MD * Andreas Rolf, MD * Andreas Blaha **
*Kerckhoff Heart and Thorax Centre Bad Nauheim, Germany
**Business Unit CT Healthcare, Forchheim, Germany
 |  2011-03-10


A 28-year-old female patient (weight 55 kg, height 175 cm, Body Mass Index 18) presented with chest pain and shortness of breath under exertion. Additionally, she complained about backache that had initially occurred a few hours before admission.
She had an elevated blood pressure of 160/100 mmHg. D-Dimer testing showed very slightly elevated values (1.1 x upper-normal value), Troponin T was negative. The ECG documented no relevant S-T elevations. Because of the multiple but typical symptoms and the equivocal laboratory and ECG findings we referred the patient for ECG-triggered CT to rule out pulmonary embolism, aortic dissection and coronary artery disease (CAD).


The examination was performed using a SOMATOM Definition CT scanner. In order to obtain optimal image quality with a low radiation dose, nitroglycerine was given sublingually immediately prior to the examination.
At a heart rate of 61 bpm, a prospectively ECG–triggered scan was performed from the aortic arch to the diaphragm at a tube voltage of 80 kV and a tube current of 215 mAs. With an estimated radiation dose of only 0.94 mSv (using published conversion factor of 0.014¹) outstanding image quality could be achieved. With the CT Angiography coronary artery disease could be ruled out as well as pulmonary embolism and aortic dissection. Due to these results from the CT scan, no further medical treatment was necessary and the patient was discharged from hospital a few hours later.



Using an individually adapted scan protocol with prospective ECG–triggering, the SOMATOM Definition CT scanner allows accurate assessment of coronary arteries and intra–thoracic vessels with one Triple Rule-Out Examination providing excellent image quality at a very low radiation dose.

¹ See DLP in examination protocol

Examination Protocol (Dual Energy Lung PBV)

Scanner SOMATOM Definition
Scan mode Triple Rule Out
Scan area Thorax
Scan length 186 mm
Scan direction Cranio-Caudal
Scan time 14 s
Tube voltage 80 kV
Tube current 356 mAS/Rot
CTDIvol 3.58 mGy
DLP 67 mGy*cm
Rotation time 0.33 s
Slice collimation 64x0.6 mm
Slice width 0.75 mm
Spatial Resolution 0.33 mm
Reconstructed increment 0.4 mm
Reconstruction kernel B26f
Volume 140 ml
Flow Rate 7 ml/sec
Start delay 20 s

The information presented in this case study is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any health care practitioner reading this information is reminded that they must use their own learning, training and expertise in dealing with their individual patients. This material does not substitute for that duty and is not intended by Siemens Medical Systems to be used for any purpose in that regard.

The drugs and doses mentioned herein are consistent with the approval labeling for uses and/or indications of the drug. The treating physician bears the sole responsibility for the diagnosis and treatment of patients, including drugs and doses prescribed in connection with such use. The Operating Instructions must always be strictly followed when operating the CT System. The source for the technical data is the corresponding data sheets. Results may vary.


Effective Dose was calculated using the published conversion factor for an adult chest of 0.014 mSv mGyˉ1cmˉ1 [1].


[1] McCollough CH et al. Strategies for Reducing Radiation Dose in CT, Radiol Clin N Am 47 (2009) 27–40