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Cardiac imaging using IQon Spectral CT

White Paper
Philips CT Clinical Science Philips Healthcare • USA

Purpose

Philips IQon Spectral CT, the world’s first and only detector-based spectral technology, is the only dual-energy solution that provides layers of spectral data without compromise. This paper demonstrates the use and performance of IQon with Philips iPatient technology at a premier healthcare institution in China.

MDCT in cardiac imaging

The use of multi-detector CT (MDCT) for cardiac imaging has become more prevalent, making it the standard clinical test for a variety of cardiovascular conditions. With its high sensitivity and negative predictive value, cardiac CT has become the noninvasive modality of choice for the assessment of coronary artery disease (CAD) and its impact on cardiac function and perfusion.1 Additionally, cardiac CT aids in the quantification of coronary plaque, the assessment of stents for in-stent restenosis, and the planning of complex coronary and structural interventions such as transcatheter aortic valve implantation (TAVI).

Challenges to cardiac imaging
There are multiple challenges in imaging coronary arteries. These arteries are typically small, with a caliber approaching 1 mm in size at their most distal ends. These small vessels exhibit complex 3D motion during the cardiac cycle, which is a major cause of artifacts during coronary imaging.2,3 This requires MDCT scanners to have the speed necessary to capture cardiac anatomy, good spatial resolution to visualize the small structures of coronary arteries, and fast gantry rotation (i.e., excellent temporal resolution, which is critical to imaging moving structures).

IQon Spectral CT in cardiac imaging
IQon Spectral CT is built upon the iPatient platform. With enhanced spectral capabilities and fast rotation speed (0.27 sec, standard temporal resolution of 135 ms in Step & Shoot Cardiac with added improvements via adaptive multi-cycle reconstruction in helical), IQon Spectral CT is ideally suited to address cardiac imaging challenges. Spectral results such as, but not limited to, monoenergetic (MonoE) and iodine no water, are always available either prospectively or retrospectively along with the standard conventional results.

Philips iPatient scanner platform
The Philips iPatient scanner platform enables users to achieve consistent cardiac image quality every day while managing dose appropriately. This intuitive user interface provides features that facilitate the use of patient-specific dose management tools for increased diagnostic confidence, while at the same time helping to improve workflow and efficiency with integrated functionality designed to enhance real-time decision-making.

Spectral CT vs conventional CT
In contrast to conventional results which represent polychromatic X-ray, MonoE results (also Hounsfield Unit [HU]-based) show attenuation as if a single monochromatic energy (keV) was used to scan. These results can be displayed in real time, representing 161 different single-energy levels between 40 and 200 keV. These MonoE results have multiple applications such as boosting of iodine signal (low MonoE), improvement of contrast-to-noise ratio (CNR) (low MonoE), and reduction in calcium blooming, beam hardening and metal artifact (high MonoE).

Unlike MonoE, which is an HU-based image, iodine no water is a material density image that represents the iodine component with the water component suppressed. The iodine content is shown within a Region of Interest (ROI) and reported in mg/ml. In general, while iodine no water is typically used to show iodine uptake, it has also been shown to enable assessment of the coronary arteries in the vicinity of calcium, while at the same time maintaining contrast enhancement in the lumen.

IQon Spectral CT at PUMCH
Peking Union Medical College Hospital (PUMCH, Beijing, China) was founded in 1921 by the China Medical Board. It is a Class A tertiary comprehensive hospital committed to delivering state-of-the-art clinical care, performing innovative scientific research and providing rigorous medical education. Designated by the National Health and Family Planning Commission as one of the national referral centers offering diagnostic and therapeutic care of complex and rare disorders, it is considered nationally a leader in diagnostic medical imaging. It maintains an excellent reputation for its full range of disciplines, cutting-edge technologies and outstanding specialties, consistently topping the “Best Hospitals in China” rankings since 2009.
PUMCH
PUMCH

As an early adopter of IQon Spectral CT, PUMCH has gained a tremendous amount of experience in non-invasive cardiac imaging, having scanned more than 1,500 patients on IQon. With the help of the dose management tools of the iPatient platform, scan and injection protocols were continuously adapted for patient body habitus (based on height, weight and body mass index [BMI]). Cardiac dose management tools such as Step & Shoot Cardiac and ECG-tube modulation in helical scans were employed for radiation dose optimization.

As part of planning the diagnostic scan, the water equivalent diameter (WED) was detected from the surview (scout) based on which the DoseRight index (DRI) was calculated to optimize the tube output (mAs) to deliver consistent image quality. The energy output of the tube was set to 120 kVp, with the mAs determined using the DRI based on the WED from the surview. Because spectral is always on, low MonoE spectral results were used to boost contrast enhancement. This allowed for cardiac CT scans to be performed at lower prescribed thresholds of contrast volume, with only 36 ml of contrast medium along with 20 ml saline chaser injected at a flow rate of 3 ml/sec. An automated bolus-tracking technique was used to start data acquisition, with scans triggered six seconds after a threshold of 90 HU was reached in the descending aorta.

All scans were successfully performed, with a mean attenuation of 350 HU obtained in the aortic root (as measured with conventional results) across all cases. This value was further enhanced with the use of low keV MonoE spectral results (720 HU using 50 keV and 495 HU with 60 keV), which further helped with the coronary assessment. The optimized protocols resulted in coronary CTA scans of high quality, with 97% of the scans considered diagnostic. The reasons for non-diagnostic results are attributable to circumstances widely published in clinical literature (such as coronary motion).4-6

The robust performance of the IQon Spectral CT for cardiac imaging is demonstrated via the following examples:
Case study 1
This case study demonstrates the capability of IQon Spectral CT in performing low-dose cardiac examinations. A middle-aged male patient on medication for suspected cardiac disease and complaining of occasional chest pain underwent coronary CT angiography (coronary CTA) using Step & Shoot Cardiac (effective dose: 0.85 mSv, k = 0.014)*. A total contrast volume of 30 ml was injected at 3 ml/sec. Using the spectral Comprehensive Cardiac Analysis (sCCA) application on IntelliSpace Portal, spectral images such as MonoE 50 keV and iodine no water clearly demonstrate the small non-calcified plaque in the RCA. Analysis (sCCA) application, available on IntelliSpace Portal, curved multi-planar reformation (cMPR) images were generated using conventional and spectral results such as MonoE 50 keV for better visualization and characterization of structures based on spectral attenuation properties. A small non-calcified plaque was seen in proximal right coronary artery (RCA) that was well visualized using the MonoE 50 keV and iodine no water spectral results.

*Using AAPM Technical Report 96.

Case study 2
A middle-aged male patient with a history of hypertension and smoking complained of acute chest pain. His electrocardiogram (ECG) indicated myocardial infarction of the posterior wall and he underwent invasive coronary angiography with stents implanted in the RCA and the left circumflex (LCX). Because of recurring chest pain, he underwent coronary CTA using IQon. cMPR images of the LCX in the stent region were reviewed using conventional and spectral results, using sCCA application on the IntelliSpace Portal. The ability to perform an assessment of the lumen within the stent was extremely limited using the conventional image in spite of adjusting the window and level. The high MonoE (150 keV) result reduced the blooming artifact arising from the struts of the stent but at the expense of decreased contrast enhancement. The low MonoE (50 keV) result provided the benefit of increased contrast enhancement, with some indication of low enhancement in the proximal area of the stent but accompanied by increased blooming off the stent. In contrast, the iodine no water image clearly showed a drop in the enhancement in the proximal end of the stent and with reduced blooming off the stent struts. Additionally, a review of the short-axis images showed the presence of sub-endocardial defect in the inferior and inferolateral walls of the myocardium (RCA and LCX territories), more clearly seen in the spectral results (low MonoE 50 keV), with the Z Effective image showing the relevant color map.

Case study
A middle-aged female patient with a history of hypertension and symptoms of back pain and intermittent chest discomfort underwent a coronary CTA using IQon for the evaluation of coronary arteries. All coronary artery segments were assessed, with an ostial lesion of the RCA found (as shown in the cMPR view). In addition, an irregular thickening of the pericardium was observed that included a large tumor occupying the mediastinal area. Spectral tools were very helpful in examining the heterogeneous composition of this pericardium-occupying mass. In contrast to the conventional image, spectral low MonoE (40 keV), iodine no water and Z Effective images provided better visualization of the hypodense core of this mass. Drawing ROI (S1, S2 and S3) in three different areas helped differentiate these areas further, with the pericardial muscle (S1, S2) showing an iodine uptake at low MonoE with the central region (S3) showing a downward slope (or no iodine uptake – indicating a necrotic core). Based on the findings, a CT-guided pericardiocentesis biopsy was performed along with immunohistochemical staining analysis, which confirmed the existence of mesothelioma.

Conclusion

Spectral results from IQon Spectral CT offer additional clinical insights for assessment of cardiac diseases. Spectral results such as MonoE and iodine no water improved visualization of complex cardiac structures compared to conventional images. The case examples shown here demonstrate the benefits of IQon Spectral CT – with spectral information always available, prospectively and retrospectively.

Clinical relevance

Philips IQon Spectral CT with iPatient technology improves diagnostic confidence in everyday clinical practice by enabling assessment of various cardiac diseases and their impact on function.

All images courtesy of Prof. Yining Wang and Prof. Zhengyu Jin, PUMCH.

References

  1. Scot-heart T. CT coronary angiography in patients with suspected angina due to coronary heart disease (SCOT-HEART): An open-label, parallel-group, multicentre trial. Lancet. 2015;385:2383–2391.
  2. Vembar M, Garcia MJ, Heuscher DJ, Haberl R, Matthews D, Böhme GE, Greenberg NL. A dynamic approach to identifying desired physiological phases for cardiac imaging using multislice spiral CT. Med Phys. 2003 Jul;30(7):1683-93. PMID:12906185.
  3. Vembar M, Walker MJ, Johnson PC. Cardiac imaging using multislice computed tomography scanners: Technical considerations. Coron Artery Dis. 2006 Mar;17(2):115-23. PMID:16474229.
  4. Neefjes LA, Dharampal AS, Rossi A, Nieman K, Weustink AC, Dijkshoorn ML, Ten Kate GJ, Dedic A, Papadopoulou SL, van Straten M, Cademartiri F, Krestin GP, de Feyter PJ, Mollet NR. Image quality and radiation exposure using different low-dose scan protocols in dual-source CT coronary angiography: Randomized study. 2011 Dec;261(3):779-86. doi:10.1148/radiol.11110606. PMID:219696662.
  5. Leschka S, Stolzmann P, Desbiolles L, Baumueller S, Goetti R, Schertler T, Scheffel H, Plass A, Falk V, Feuchtner G, Marincek B, Alkadhi H. Diagnostic accuracy of high-pitch dual-source CT for the assessment of coronary stenoses: First experience. Eur Radiol. 2009 Dec;19(12):2896-903. doi:10.1007/s00330-009-1618-9. PMID:197602293.
  6. Budoff MJ, Achenbach S, Duerinck A. Clinical utility of computed tomography and magnetic resonance techniques for noninvasive coronary angiography. J Am Coll Cardiol. 2003 Dec 3;42(11):1867-78. PMID:14662244.


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White Paper
IntelliSpace Portal, IQon Spectral CT
calcium, Cardiac, chest pain, Comprehensive Cardiac Analysis, coronary angiography, coronary arteries, coronary artery disease, curved MPR, DoseRight, Effective Z, hypertension, image quality, Interventional, iodine no water, iPatient, lesion, low dose, MonoE, myocardial perfusion, plaque, prospective, RCA, retrospective, spectral CT, stenosis, stent, Step & Shoot Cardiac, TAVI, Vascular
 

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