Dual Energy Coronary CT Angiography for Evaluation of Chest Pain after RCA Revascularization

Ralf W. Bauer, MD, J. Matthias Kerl, MD, Thomas J. Vogl, MD,
Goethe University, Department of Diagnostic and Interventional Radiology, Frankfurt/Germany
 |  2010-07-07

History

A 54-year-old female patient underwent coronary stent percutaneous transluminal coronary angioplasty (PTCA) of the right coronary artery (RCA) four months ago for acute ST-elevation myocardial infarction of the inferioseptal wall. Now, the patient suffered from reduced physical power and labile blood pressure and had an event of syncope three weeks ago. Invasive coronary angiography was performed to assess stent patency. In-stent occlusion of the mid and distal RCA with moderate collateralization from the left anterior descending (LAD) and left circumflex artery (LCX) and a patent right ventricular (RV) branch were found (Fig. 1).
Recanalization was performed with placement of 2 drug-eluting stents in the distal and mid RCA. During intervention, a small contrast material extravasation was seen near the ostium in the proximal RCA.
A small intima dissection was suspected and another stent was placed to close the leakage.
Three hours after intervention, the patient developed chest tightness and retrosternal pain.
ECG showed signs of the known old infarction inferiorseptally (Q waves in II, III and aVF) but no signs of acute ischemia. She was sent to CT to rule out aortic dissection.
 

Diagnosis

Cardiac CT was performed in Dual Energy mode with retrospective ECG-gating. There was no sign of contrast material extravasation or aortic dissection. Dual Energy CT angiography revealed in-stent thrombosis with occlusion of the RCA 13 mm after its origin (Figure 2). While on cardiac cath the RV branch was still open, DECT showed an occlusion of the vessel due to the thrombus in the proximal RCA explaining the patient’s symptoms. Dual Energy myocardial iodine mapping showed a large hypoperfused area inferoseptal extending from the base down to the apex (Figure 3). Low-dose step-and-shoot late enhancement images 7 minutes after contrast injection showed corresponding delayed contrast material wash-out (Figure 1). On regular anatomical multiplanar reformates a moderate thinning of the left ventricular myocardium was present in that area (Figure 4).
 

Comments

In this case, Dual Energy coronary CT angiography was used to image a complication of interventional recanalization, i.e. acute in-stent thrombosis, while the initial clinical diagnosis of acute aortic dissection could reliably be ruled out. Due to the large thrombus formation beginning very proximally in the RCA, a further complication was the occlusion of the RV branch, which was patent prior to intervention. The new hybrid reconstruction algorithm for coronary CTA images preserves the high temporal resolution of 75 ms of the Dual Source system and allows for motion-free imaging of the vascular structures. According to the clinical history of the patient, assessment of the myocardium with Dual Energy first-pass perfusion and late enhancement imaging showed signs of chronic infarction in the inferoseptal wall of the left ventricle. Increased tube power as well as improved separation of the spectra by using a tin filter (140 kV + Sn) allow for artifact-free imaging of myocardial perfusion. Complete diagnostic work-up of the coronary arteries and the myocardium was achieved with a total dose length product of only 294 mGycm (227 mGycm CTA + 67 mGycm late enhancement).
 

Examination Protocol

Scanner SOMATOM Definition Flash
Scan mode Dual Energy
Scan area Heart
Scan length 155 mm
Scan direction Cranio -Caudal
Scan time 4.8 sec
Tube voltage 110 kV/ 140 kV
Tube current 165 mAs/ 140 mAs
CTDIvol 13.29 mGy
DLP 205 mGy/cm
Effective Dose 2.88 mSv
Rotation time 0.28 s
Slice collimation 64 x 0.6 mm
Slice width 0.75 mm
Reconstruction increment 0.4 mm
Reconstruction kernel D26f
Contrast  
Volume 70 ml
Flow rate 5 ml/s
Start delay Test bolus

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 labelling 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 a 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