Multi-Slice CT for Coronary Calcium Scoring and Coronary Angiography

John D. Symanski, M.D., F.A.C.C

The Sanger Clinic, PA and Carolinas Medical Center

No Disclosures

Objectives

• Show lots of pretty pictures

• Overview fundamental principles of MSCT technology

• Review strengths and limitations of MSCT

• Raise awareness of current indications and clinical scenarios for which to consider CT angiography

Case Presentation

• 64-year-old female with stage 1 CLL

• Dyslipidemia (untreated); No HTN, diabetes, or tobacco use

• Negative stress echo previously

• Atypical chest pain

• Stress echo: septal hypokinesis at rest, LVEF: 50%

• Referred for calcium scoring and CTA

CT Angiogram Interpretation

• Calcium Volume Score: ZERO

• CT angiography:

– Left Main, Circumflex, and Right coronary arteries: normal

– LAD: eccentric, soft plaque adjacent to origin of first diagonal (~60% stenosis)

• Correlation recommended

SummaryCardiovascular Imaging - State of the Art

• Multi-slice CT (MSCT) not likely to replace conventional angiography

• Post-processing of images for MSCT angiography time & labor intensive

• Major strength of CTA is its high negative predictive value

• CMR to become the preferred cardiac imaging modality in the future

Which Test for Which Patient?

• All modalities are improving

• No single modality fits all applications and all patients

• Choice of initial test depends on the specific clinical question in individual patient

Cardiac Magnetic Resonance

Viability AssessmentCMR Delayed Hyper-Enhancement

Hazards of MRIMagnet-Seeking Projectiles

First whole-body CT cross-section through a human thorax, generated by Ledley et al in 1974 (Science 1974;186:207)

The Examination

Current Generation Scanners

• Spatial resolution 0.4 mm - conventional coronary angiography 0.15-0.25 mm

• Temporal resolution (shutter speed) improved to 166 msec with faster gantry rotation (330 msec) – conventional angiography 6 msec

• Up to 64 slices in one rotation

4 to 64 Slice ScansFive Heart Beats

10 mm detectorPitch ~0.25

3 cm in 5 sec

20 mm detectorPitch ~0.25

6.2 cm in 5 sec

40 mm detectorPitch ~0.25

12.5 cm in 5 sec

64-Slice CT Scanner

• More coverage (volume) with each heart beat

• Entire heart imaged in 5-15 seconds

• Less contrast required

• No increase in rotation speed, but with overlapping slices, can use segments from different heart beats to improve temporal resolution

3-D Volume Rendered Image

Maximum Intensity ProjectionSoft Plaque in Proximal LAD

Curved Planar Image

Quantification of Obstructive and Nonobstructive Coronary Lesions by 64-Slice

Computed Tomography

• 59 patients with stable angina subjected to CTA before catheter-based angio

• Diagnostic image quality in 55 of 59• Sensitivity for detection of stenosis

<50%, >50%, and >75%: (79%, 73%, and 80%, respectively)

• Excellent accuracy with proximal lesions

Leber AW et al. J Am Coll Cardiol. July 5, 2005;46:147-54

Diagnostic Accuracy of Noninvasive Coronary Angiography Using 64-Slice

Spiral Computed Tomography• 70 patients undergoing invasive cath• Of 1,065 segments, 935 evaluated (88%)• Quantitative assessment in 773 of 935

segments by MSCT and QCA• Sensitivity, specificity, (+) PV, (-) PV:

– By segment- (86%, 95%, 66%, and 98%)– By artery- (91%, 92%, 80%, and 97%)– By patient- (95%, 90%, 93%, and 93%)

Raff GL et al. J Am Coll Cardiol. Aug 2, 2005;46:552-7.

Coronary Calcium Scoring

• Initial ACC/AHA guidelines “may be useful in selected patients”…

• Added prognostic power to conventional risk stratification tools (Framingham)

• Revised guidelines (and reimbursement for service) likely forthcoming

Hn x-factor(Agatston Scoring)

130-199 1

200-299 2

300-399 3

>400 4

Area = 15 mmArea = 15 mm22

Peak CT = 450Peak CT = 450Score = 15 x 4 = 60Score = 15 x 4 = 60

Area = 8 mmArea = 8 mm22

Peak CT = 290Peak CT = 290Score = 8 x 2 = 16Score = 8 x 2 = 16

Total Score = S

Calcium Volume Scoring

The Calcium Scale

The calcium scale is a linear scale with 4 calcium score categories:

0 none

1–99 mild

100–400 moderate

>400 severe

*Calcium score correlates directly with risk of events and likelihood of obstructive CAD*

Ethnic Differences in Coronary CalcificationThe Multi-Ethnic Study of Atherosclerosis (MESA)

Bild DE et al. Circulation. 2005;111:1313-1320.

6814 men and women aged 45-84 years

Five-Year Mortality Rates in Framingham Risk Subsets by Coronary Calcium Score

Shaw et al. Radiology 2003; 228:826-833

*

*

**p<0.001

• MI in 41 pts during 3.2 + 0.7 years

• LDL levels similar in MI and non-MI pts

• Relative risk of MI in presence of CAC progression was 17.2-fold higher (P<0.0001)

Progression of Coronary Artery Calcium and Risk of First MI

495 Asymptomatic Patients Started on Statin Therapy

Raggi P et al. Arterioscler Thromb Vasc Biol. 2004;24:1272-77.

Coronary Disease Progression

? Role for CTA >60% stenosis (+)

stress/imaging

Calcified Plaque Detected by CT

Soft Plaque Visualization

CTA Limitations

• Rapid (>80 bpm) and irregular HR

• High calcium scores (>800-1000)

• Stents

• Contrast requirements (Cr > 2.0 mg/dl)

• Small vessels (<1.5 mm) and collaterals

• Obese and uncooperative patients

• RADIATION EXPOSURE

Effective Dose of Selected Radiologic Examinations

• PA/Lateral CXR 0.04-0.06 mSv

• Head CT 1-2 mSv

• Chest CT 5-7 mSv

• Abd/Pelvis CT 8-11 mSv

• Diagnostic Cor Angiogram 3-5 mSv

• MSCT angiography 9.3-11.3 mSv

Morin et al. Circulation 2003;107:917-22.

*Average annual background radiation in U.S ~ 3.6 mSv

Radiation Risks

• Exact quantification of harmful effects of radiation difficult to ascertain

• For a child under age 15, the risk of cancer death from a single CT scan is approximately 1 in 500

• For a 45 year old adult, the risk of death from cancer from a single CT exam is about 1 in 1,250

Brenner et al. Radiology, 231(2):440-445.

Clinical Indications for MSCT

• Calcium Scoring (CS) - risk stratification in the intermediate risk patient

• Non-invasive coronary angiography (CTA) in the symptomatic low-risk patient or asymptomatic intermediate-risk patient*A negative test (normal CTA) has a 98% chance of revealing normal coronary arteries on invasive angiography*

Test Selection According to Pretest Probability of CAD

Association for the Eradication of Heart Attacks (AEHA.org)

When to Consider MSCT

• Equivocal stress test or persistent symptoms despite negative stress test

• Prior to non-coronary cardiac surgery (valve or congenital repair)

• Patients with difficult access or on therapeutic warfarin

• Suspected coronary anomalies

Lt Main

CFX

RCA

LAD

• Idiopathic dilated cardiomyopathy

• Cardiac transplant evaluation

• Patients to undergo electrophysiologic intervention (AF ablation, BiV pacing)

• Selected patients pre- and post-bypass surgery (aortic pathology, graft patency)

When to Consider MSCT(continued)

Mikaelian BJ et al. Circulation. 2005;112:e35-e36.

Pulmonary Vein Stenosis

Vasamreddy et al. Heart Rhythm (2004) 1, 78-81.

Aortic Coarctation Visualized by 16-Row Detector MSCT

Fröhlich, G et al. Circulation. 2005;112:e81.

Pericardial CalcificationMulti-Slice CT Scanning Superior to MRI

Hoffmann et al. Circulation 108 (7): 48e Figure IG1

Nikolaou et al. Cardiology Clinics. 21;(2003):639-655.

Future Indications

The Great Promise of MSCTThe “Triple Rule-Out”

“an appropriate imaging study is one in which the expected incremental information together with clinical judgment exceed the expected negative consequences* by a sufficiently wide margin that the procedure is generally considered acceptable care and a reasonable approach for the indication.”

Appropriateness Criteria

*include risks of the procedure and the downstream impact of poortest performance such as delay in diagnosis (false -) or inappropriatediagnosis (false +)