Non-Invasive Coronary Angiography;

The Future Is Here “Fast MSCT”!

Provided by:

Alireza Zarrabi, M.D.Center for Vulnerable Plaque Research,

Texas Heart Institute and University of Texas - Houston

Editorial Slides VP Watch – October 16, 2002 - Volume 2, Issue 41

1979 Nobel Prize in Medicine and Physiology went to Hounsfield and

McCormack for invention of computed tomography.

Godfrey Hounsfield Allan MacLeod Cormack

Non-invasive imaging of coronary arteries has been a dream for cardiovascular medicine that is now coming close to reality.

However, imaging of small arteries (coronaries) on a moving target body (heart) is a complicated and challenging situation.

There is no time in which all portions of the

heart are at rest and this fact contributes to limitations for any tomographic imaging method that requires fixed exposure time.

CT, EBCT, and MRI are competing techniques for non-invasive imaging of coronary arteries.

Each of the above technology has some advantages and disadvantages that prevent them from being a unique solution superior to the others to completely serve the purpose of non-invasive diagnosis of future culprit lesions (vulnerable plaque) as a widely available clinical tool.

MR angiography has been a progressive process in recent years.

n Sensitivity Specificity

Post et al 1996 20 38% 95%Müller et al 1997 30 83% 94%Achenbach et al 1997 73 65% 88%Sandstede et al 1999 30 81% 89%van Geuns et al 1999 32 50% 91%Leithmonnier et al 1999 20 65% 93% Sardanelli et al 2000 42 82% 89%Regenfus et al 2001 50 87% 91%Kim et al 2001 107 83% 73%

The feasibility of MRI to quantify plaque morphology has been demonstrated ex vivo in human carotid tissue and in vivo in animal models. 1,2

MR Imaging and MR Angiography :

Advantages Non-invasive No need for contrast media Detailed plaque characterization

Disadvantages Poor spatial resolution Inadequate temporal resolution High cost

Milestone in CT

1967 Pattern recognition and reconstruction techniques using computer – G. Hounsfield

1971 The first clinical prototype CT brain scanner – Ambrose

1974 The first whole-body CT scanner – Robert Ledley

1979 Nobel Prize in Medicine and Physiology – Hounsfield and MacLeod Cormack

1979 The first principle and operation of the electron beam CT (EBCT) scanner – Douglas Boyd

1983 The first EBT scanner developed by Imatron and named cardiovascular computed tomography

1988 The first coronary calcium study

1989 The first report of a practical spiral CT scanner (single-slice spiral CT)– Willi Kalender

1992 Dual-slice spiral CT scanner

1995 The first CT coronary angiography

1998 Multi-slice CT scanner

In old conventional CT the x-ray tube and detectors rotate for 360 degrees or less to scan one slice while the table and patient were stationary which was time consuming.

In next generation In 1989 the first report of a practical spiral CT scanner was presented at RSNA meeting by Dr. Willi Kalender.

The next step forward has been the introduction of multi-slice CT (MSCT) scanner at the RSNA 1998.

CT screening has been the center of attention in the field of clinical diagnostic imaging during the past few years for different purposes such as coronary artery calcification, lung cancer, colonoscopy, and whole body scan.

CT claims several applications in the field of cardiovascular imaging: Coronary calcium imaging CT angiography Assessment of cardiac function

Electron beam computed tomography (EBT) can accurately identify presence of calcification in the coronary tree non-invasively.

Coronary calcification is not normal and clearly indicates presence of atherosclerosis.

Rumberger et al. stated important conclusion for using EBT: 6,7

Coronary calcium area per individual coronary artery and/or per whole heart as defined by EBT is highly correlated with histologically quantified coronary plaque area.

Guerci, Arad, and colleagues also found that in asymptomatic adults, EBCT of coronary arteries predicts coronary death and nonfatal MI and the need for revascularization procedures. 4

Rumberger and others showed the ranges for EBT coronary calcium score cutpoints that predict the likely severity of associated maximal angiographic stenosis severity to a high sensitivity, high specificity or optimal sensitivity/specificity. 5

Dr. AradDr. Guerci

Budoff, Raggi, and colleagues showed that EBT calcium scanning provides incremental and independent power in predicting the severity and extent of angiographically significant CAD in symptomatic patients, in conjunction with pretest probability of disease. 3

# of patients Sens. Spec.

Nakanishi et al. 1997 37 74% 91%Schmermund 1998 28 82% 88%Achenbach 1998 125 92% 94%Ropers 2000 118 90% 82%Achenbach 2000 36 92% 91%

Achenbach 1999 56 Occlusion 100% 100%

Stenosis 100% 97%

Sensitivity and Specificity of EBCT for Obstructive Coronary Disease As Compared With Invasive

Coronary Arteriography

Achenbach et al. for the first time established a protocol for the visualization of coronary arteries by EBT. 8

EBT has been used as a noninvasive 3D arteriography of the large epicardial coronary arteries, to visualize coronary artery bypass grafts, and also to characterize coronary artery anomalies.

CT Angiography

EBT MSCT

True temporal resolution 50-100 ms 230-1000 ms

Spatial resolution 1.5 mm vessels 1.0mm vessels

Practical heart rate limitations for a Dx study

50-100 bpm <60-65 bpm

Cardiac function & myocardial perfusion

Yes No

Radiation exposure, mSv 1-2 2-10

Clinical availability Increasing slowly Expanding rapidly

Coronary calcium quantitation

Yes, extensively validated Yes, limited validation

EBT vs. MSCT

Adapted from: Noninvasive Coronary Angiography Using Computed Tomography: Ready to Kick It Up Another Notch? Circulation. 2002 Oct 15;106(16):2036-2038

Comparing MSCT and Invasive Angiography

n Sens SpecNieman et al 2001 31 81% 97%Achenbach et al. 2001 64 91% 84%Knez et al. 2001 42 78% 98%Nieman et al. 2002 59 95% 86%

As reported in VP Watch of this week, Nieman and colleagues performed ECG-gated MSCT angiography with a 16-slice MSCT scanner (0.42-s rotation time, 12x0.75-mm detector collimation) in selective patients with suspected obstructive coronary artery disease.

Additional ß-blockers were given 1 hour before the procedure to those patients with a resting heart rate >65 beats/minute. Average heart rate during study was 56 beats/min.

MSCT scanner used for this study has a rotational speed of 440 ms and can achieve cardiac tomographic slice thicknesses of <1.0 mm.

They showed the overall sensitivity and specificity to detect significantly stenosed coronary arteries was 95% and 86%.

The predictive value of MSCT angiography to detect patients with no, single, or multivessel disease in this study was 100%, 75%, and 74%, respectively.

Conclusion:

The use of 16-slice CT scanner with 400ms rotation time, combined with ß-blocking agent has significantly improved the diagnostic accuracy of MSCT to non-invasive detection of coronary stenosis.

Fast MSCT is moving fast to become the first screening imaging technique for detection of coronary artery disease.

Questions:

Which one of the following should be considered as first step imaging in screening for vulnerable plaques in vulnerable patients?

EBT

MSCT

MRI / MRA

Questions: Despite improvements in rotational

acquisition speed above most current helical scanners, resting heart rate would still be a major factor in image quality by MSCT. What is the next step:

Faster CT (decrease rotation time)?

Or Larger detectors (32, 64, or more slices)?

1) J.F. Toussaint, G.M. LaMuraglia, J.F. Southern, V. Fuster and H.L. Kantor, Magnetic resonance images lipid, fibrous, calcified, hemorrhagic, and thrombotic components of human atherosclerosis in vivo. Circulation 94 (1996), pp. 932¯938.

2) S.G. Worthley, G. Helft, V. Fuster, Z.A. Fayad, O.J. Rodriguez, A.G. Zaman, J.T. Fallon and J.J. Badimon, Noninvasive in vivo magnetic resonance imaging of experimental coronary artery lesions in a porcine model. Atherosclerosis 150 (2000), pp. 321¯329.

3) Continuous probabilistic prediction of angiographically significant coronary artery disease using electron beam tomography. Circulation. 2002 Apr 16;105(15):1791-6.

4) Prediction of coronary events with electron beam computed tomography. J Am Coll Cardiol. 2000 Oct;36(4):1253-60.

5) Electron beam computed tomographic coronary calcium score cutpoints and severity of associated angiographic lumen stenosis. J Am Coll Cardiol. 1997 Jun;29(7):1542-8.

6) Rumberger JA, Sheedy PF, Breen JF. Use of ultrafast (cine) x-ray computed tomography in cardiac and cardiovascular imaging. In: Giuliani ER, Gersh BJ, McGoon MD, et al, eds. Mayo Clinic Practice of Cardiology. 3rd ed. St. Louis, Mo: Mosby; 1996: 303–324.

7) Rumberger JA, Simons DB, Fitzpatrick LA, et al. Coronary artery calcium areas by electron beam computed tomography and coronary atherosclerotic plaque area: a histopathologic correlative study. Circulation. 1995; 92: 2157–2162

8) Achenbach S, Moshage W, Bachmann K. Coronary angiography by electron beam tomography. Herz. 1996; 21: 106–111

References