Cardiac CT-CCTADr.Sahar Gamal El-

Din ,CBCCTNational Heart Institute

Performing CCT

Patient Preparation:Ensure patient comfort•Explain breathing instructions clearly•Discuss contrast effects•Antecubital IV 18-20g suggested•Beta-blockade•Target heart rate 50-65 bpm•Nitroglycerine

Initial Scanning: Ca Score1. Helps to identify how the

coronary vessels will behave (especially the RCA) during the scan.

2. Points out the “ possible” atherosclerotic vascular tree.

3. High Ca score is not equivalent to “not to perform the test ( but be wise ).

Coronary Disease ProgressionCalcified Plaque Detected by

CT

• Atherosclerosis is the only disease process known to cause calcium to deposit in coronary artery walls.

• Calcification is not a degenerative disease, it is not a part of the “normal” aging process.

• Calcium is not found in normal

CA.Radiology 2002; 223:474–480.

• Since calcium deposits start to develop during the early stages of atherosclerosis and if we are able to identify the presence of calcium we are able to identify preclinical coronary artery disease during the asymptomatic stage.

• This can allow for the implementation of early aggressive risk factor reduction.

• Coronary artery calcification has been shown to be a marker for coronary artery atherosclerosis .

• Calcification can be seen with fluoroscopy and on chest x-ray.

• Computed tomography allows quantification of this calcium.

• The amount of calcium deposited in coronary arteries is added up and a “score” is given.

• The amount of calcium in the coronary arteries varies considerably with age and gender.

• For this reason, coronary calcium scores are presented as percentile scores telling you how much calcium you have compared to other men or women of your age.

Methods• Agatston Score :Traditional

method (EBCT : MDCT)

• Volume Score : Plaque area x slice thickness (mm³)

• Mass Score : Plaque volume x mean plaque density .

The Calcium Scale

The calcium scale is a linear scale with 5 calcium score categories:

0 none 1–99 mild

100–400 moderate >400 severe >1000 extensive

calcification

Image acquisition and reconstruction

• The acquisition of the dataset for coronary CTA consists of 3 steps :

1. Topogram

2. Contrast medium protocol : to ensure homogeneous contrast enhancement of the entire coronary artery tree

3. Coronary CTA scan

Topogram• Native coronary arteries # Begin 1–2 cm below the

carina # Tortuous aorta or

prominent upper left heart border – begin scan 1-2cm higher

• Bypass Grafts Veins: top of arch LIMA: above claviclesScan ending position• Image acquisition end 2

cm below the diaphragm

Scan Start Position

Contrast Injection1.Iodine Content 2.Volume3.Rate4.Synchronization Techniques:

a. Fixed Delayb. Test Bolusc. Bolus Tracking

Phase Synchronization

1.Retrospective ECG gating (Continuous Scanning).

2.Prospective ECG triggering (step-and-shoot technique).

Retrospective ECG gating

• The most commonly used data reconstruction technique

• Advantage: any desired phase of the cardiac cycle can be reconstructed

• Disadvantage: increased radiation dose

Prospective ECG gating Data are only acquired at predefined time points of the cardiac cycle when the data acquisition is considered relevant.

The X-ray tube is turned on at a priori chosen time interval from the last monitored R–R peak.

Advantage: dcreased radiation doseDisadvantage: limited information & no function

Scanning protocol

Post processing protocol• The axial source images obtained are

utilized for multiplanar reconstructions in at least 2 planes

• Commonly used techniques are :

Multiplanar reconstruction (MPR) Curved planar reconstruction (CPR) Maximum intensity projection (MIP) Volume rendering (VR)

Multiplanar reconstruction (MPR)

Curved MPR reconstruction (CMPR)

Maximum intensity projection (MIP)VRT reconstruction image

Anatomy & Views

Axial Sagital

Coronal

Normal Coronary Anatomy• Left Coronary Artery and its

Branches :• The left main artery normally arises

from the posteriorly positioned left sinus of Valsalva and bifurcates into the LAD & LCX .

• The LAD courses through the anterior interventricular groove and provides diagonal branches to the anterior left ventricle and septal branches to the anterior interventricular septum.

LMT

• The LCX gives off obtuse marginal branches (OM), which supply the lateral wall of the left ventricle.

• Occasionally, the left main artery can trifurcate into the LAD, the LCX, and a third vessel between the LAD and LCX termed the ramus intermedius artery.

• The course and vascular territory of the ramus intermedius artery are similar to those of the diagonal and/or obtuse marginal arteries.

OM

Diag.

LMT

Different types of LMCA bifurcation. Oblique transverse thin-slab maximum-intensity projection images.The LMCA is shown bifurcating into the LAD and LCX (Panel A), the LM with trifurcation into the LAD and the LCX, and in between an intermediate branch (IMB, Panel B). Note the high diagonal branch (D)from the LAD (Panel B).

Curved MPR of LAD

Curved MPR of LCX

• Right Coronary Artery and its Branches:

• The RCA arises from the anteriorly positioned right sinus of Valsalva and courses through the right AV groove.

• The conus artery is the first branch of RCA in 50% of cases, and it supplies the right ventricular infundibulum. In the remaining 50% of cases, the conus artery arises directly from the aorta.

• The sinoatrial (SA) nodal branch arises from the RCA in most patients (60%) & courses posteriorly. In the remaining patients it arises as a branch of the LCX.

• Other branches supply the right atrium and free wall of the right ventricle.

• The largest of these arises from the RCA at the acute margin of the heart and is termed the acute marginal branch.

• At the crux of the heart the RCA gives off the posterior descending artery ( PDA ), which supplies the posterior interventricular septum.

• The posterolateral branch (PLB) is a continuation of the RCA in the posterior atrioventricular groove & supplies the posterior and inferior wall of the LV

PL

Curved MPR of RCA

Maximum intensity projection (MIP)  of RCA

Dominance• Generally, the artery that supplies the

inferior 1/3 of the interventricular septum is considered to be the dominant coronary artery.

 • The RCA is dominant in most subjects

(85%), while in 7% to 8% of cases the LCX gives rise to the posterior descending artery (PDA), a left dominant system.

• In the remaining patients, a codominant, or balanced circulation, system exists; examples include a small PDA originating from the RCA with posterolateral branches from the LCX artery, and PDAs from both the RCA and LCX.

PL

Rt.Dominant

RCA

LCX

Lt.Dominant Co.Dominant

• The coronary artery nomenclature is based on the intermediate and distal vascular territory of the artery; this is particularly important when vessels are anomalous.

• In these circumstances, the proximal course or coronary origin cannot be considered when defining or naming the respective coronary artery.

• For example, a subepicardial artery that courses through the anterior interventricular groove and provides septal branches is termed the LAD, regardless of its origin from the aorta.

• Similarly, for an artery to be defined as the LCX, it should course through the left atrioventricular sulcus and provide at least one obtuse marginal (OM) branch.

• The RCA is defined as an artery that runs in the right atrioventricular sulcus and gives off RV or acute marginal branches.

Coronary artery assessment

• The best evaluated coronary artery is the LAD as it runs along the axis of the scan and is not significantly affected by cardiac movements.

• The LAD is well visualized in 76-96% of cases

• The left CX artery may be affected by cardiac motion artifacts and can be assessed in 52-95% of cases.

• RCA is most affected by cardiac movement

• Proximal coronary segments are better visualized than distal ones.

Normal Coronary Artery Diameter

–Each coronary artery vary, ranging from 5 mm (LMT in males) to 2 mm (PDA in females).

–Abnormal dilatation to more than 1.5 times the diameter of an adjacent normal coronary artery is defined as ectasia.

Coronary artery aneurysms• Classification :• Vessel wall composition• True aneurysm Vessel wall composed of three layers:

adventitia, media, and intima• False aneurysm Vessel wall composed of one or two

layers• Shape/gross structure• Saccular aneurysm Transverse > longitudinal diameter• Fusiform aneurysm Longitudinal > transverse

diameter• Giant aneurysm• Adults >20 mm–150 mm in diameter• Children >8 mm in diameter

Types of plaques1. Non-calcified 2. Partly calcified3. Mixed4. Calcified

• Positive remodelling : outward plaque growth leading to arterial wall expansion in an attempt to avoid luminal stenosis.

Eccentric - Concentric

Recommended stenosis grading

• Normal : Absence of plaque & no luminal stenosis.

• Minimal : Plaque with < 25% stenosis.

• Mild : Plaque with 25% to 49 stenosis.

• Moderate : Plaque with 50% to 69 stenosis.

• Severe : Plaque with 70% to 99 stenosis.

• Occluded.JCVCT 2014;342-358