AIM OF THE STUDYTo analyse the percentage of coronary artery stenosis with the help of C.TCoronary Angiogram.
INTRODUCTION Computed Tomography (CT combines X-radiation and radiation detectorscoupled with a computer to create cross- sectional image of any part of the body.The basic principle behind CT is that the internal structure of an object can bereconstructed from multiple projections of the body. The CT was first established as being relatively high dose X-ray imagingtechnique. At first the CT practice involved single slice scanners largely operatingin a slice-by-slice axial scanning mode. CT practice continues to evolve with theintroduction of multidetector rows to allow rapid imaging of large volume of thepatient by simultaneous acquisition of multiple slices. CT plays a central,increasingly influential role in medical imaging, the combination of faster scanningand improved image quality available with MDCT.AXIAL Vs HELICAL CT Axial is slice – by- slice scanning mode. In this, the exposure is made aftereach table incremenation according to the region scanned. Conversely, the helicalCT scanners acquire data while the table is moving as a result the X-ray sourcemoves in a helical pattern around the patient being scanned.
In helical CT, the total scan time required to image the patient can be mademuch shorter by simultaneous rotation of the X-ray tube and translation of thepatient table. Consequently, helical scanning allows the use of less contrast agentand increases patient throughput. In some instnces, the entire scan can beperformed within a single breadth hold of the patient, avoidind inconsistent levelsof inspiration. The speed of the table motion relative to the rotation of CT gantry is a veryimportant consideration in helical CT and pitch is the parameter that describes thisrelationship PITCH = TABLE MOVEMENT (mm)/360° GANTRY ROTATION NOMIAL SLICE WIDTH (mm)
CARDIAC CT Multislice CT (MSCT) is the latest technology in this decade, functioning byacquiring multiple simultaneous slices using multi-detector system. Most advancedand contemporary models are the 64-slices machine, dual source CT machine andthe 256-slices machine. One of the latest advances in CT is CT coronary angiogram all thesemachines are competing for better performance by improving the spatial andtemporal resolution. To date, a good CT machine can complete the scan in lessthan 0.3 seconds in optimal settings. Cardiac CT provides information about the heart morphology. In cardiacimaging, faster the data acquisition, better the image quality. Coronary CTA is ahighly accurate non-invasive diagnostic modality for the assessment of coronaryartery disease and its severity. CTA is a useful imaging modality for theElectrophysiological Cardiologist and Cardiac Surgeon. Coronary CTA allows forthe assessment of vessel wall morphology. Coronary CTA bridges a very large gap in diagnostic testing betweentraditional stress testing and selective coronary angiography. The extremely high
negative predictive valve of coronary CTA should reduce the number of normalcatherterization.PROSPECTIVE TRIGGERINGIt is an axial (step and shoot) mode of scanning where the acquisition is done onlyduring the diastolic phase of the cardiac cycle. (Snap Shot Pulse) X-RAY ONPROSPECTIVE TRIGGERING
PADDING In case if you suspect any variation in the heart rate, Padding can be appliedwhich exposes the patient for additional time before and after the center phase ofthe acquisition and utilizes the data for reliable reconstruction. Heart Rate Dependent Padding HR Range milli second 30 – 39 175 40 – 49 150 50 – 59 125 60> 100
RETROSPECTIVE GATING It is helical mode scanning where the acquisition is done throughout theentire cardiac cycle. (Snap Shot Segment) X-ray on Retrospectively gated reconstruction using data from 2/3 of a gantry rotationto create an image form one cardiac cycle. SNAP SHOT SEGMENT Heart rate 30 – 74 BPM Cycle 1 A retrospectively gated reconstruction, using data from 2 cardiac cycleswithin the same cardiac phase, to create an image at a given anatomic location.
SNAP SHOT BURST Heart rate 75 – 113 BPM Cycle 1 Cycle 2 A retrospectively gated reconstruction, using data from 4 cardiac cycleswithin the same cardiac phase, to create an image at a given anatomic location. Snap Shot Burst Plus Heart rate 114+ BPM Cycle 1 Cycle 2 Cycle 4 Cycle 3
Scan ResolutionThe 64 slices CT machine with narrow scan collimation provide significantlyenhances the reconstruction work of CT Coronary Angiogram.Radiation dose and Risk As the number of slices increase, radiation efficiency also increases.Radiation dose is affected by mAs (electric current of the machine) and kVp andboth have to be kept as low as possible. The radiation dose of coronary Angiogram64-slice CT machines is approximately 13-18 mSv respectively. The risk ofdeveloping severe allergic reaction with non-ionic contrast is about 0.2%-0.7% ofpatient. Single CT coronary angiogram is about 3 to 6 times the yearly radiationdose.
Spatial Resolution A good spatial resolution is important as we are scanning coronary arteries,which have diameter between 1mm to 4mm. The spatial resolution of about0.33-0.35mm is obtained by a 64-slice machine, with the isotropic voxel geometryof 0.5mm, and seems to be working well.Temporal resolution For complete motionless imaging of heart, we need the temporal resolution to be20msec. Better temporal resolution can be achieved by faster gantry (CT machine)rotation.
ANATOMY OF THE HEART AND ITS BLOOD VESSELSCORONARY ARTERIES
The two main coronary arteries are the left and right coronary arteries. The leftcoronary artery (LCA), which divides into the left anterior descending artery andthe circumflex branch, supplies blood to the left ventricle and left atrium. The right coronary artery (RCA), which divides into the right posteriordescending and acute marginal arteries, supplies blood to the right ventricle, rightatrium, sinoatrial node (cluster of cells in the right atrial wall that regulates thehearts rhythmic rate), and atrioventricular node.Additional arteries branch off the two main coronary arteries to supply the heartmuscle with blood. These include the following: • Circumflex artery (Cx) The circumflex artery branches off the left coronary artery and encircles the heart muscle. This artery supplies blood to the lateral side and back of the heart. • Left anterior descending artery (LAD) The left anterior descending artery branches off the left coronary artery and supplies blood to the front of the left side of the heart.
Smaller branches of the coronary arteries include: acute marginal, posteriordescending (PDA), obtuse marginal (OM), septal perforator, and diagonals. On theleft an overview of the coronary arteries in the anterior projection. • Left Main or left coronary artery (LCA) Left anterior descending (LAD) Diagonal branches (D1, D2) Septal branches Circumflex (Cx) Marginal branches (M1, M2) Right coronary artery o Acute marginal branch (AM) o AV node branch o Posterior descending artery (PDA). • Left Main or left coronary artery (LCA) o Left anterior descending (LAD)
Diagonal branches (D1, D2) Septal branches o Circumflex (Cx) o Marginal branches (M1, M2)• Right coronary artery o Acute marginal branch (AM) o AV node branch o Posterior descending artery (PDA)
• Left Main or left coronary artery (LCA) o Left anterior descending (LAD) Diagonal branches (D1, D2) Septal branches o Circumflex (Cx) Marginal branches (M1, M2)• Right coronary artery o Acute marginal branch (AM) o AV node branch o Posterior descending artery (PDA)
Left Coronary Artery (LCA)Left coronary (LC), right coronary (RC) and posterior non-coronary (NC) cuspThe left coronary artery (LCA) is also known as the left main.The LCA arises from the left coronary cusp.The aortic valve has three leaflets, each having a cusp or cup-like configuration.These are known as the left coronary cusp (L), the right coronary cusp (R) and theposterior non-coronary cusp (N). Just above the aortic valves there are anatomic dilations of the ascending aorta,also known as the sinus of Valsalva. The left aortic sinus gives rise to the left
coronary artery.The right aortic sinus, which lies anteriorly, gives rise to the right coronary artery.The non-coronary sinus is positioned on the right side.LCA divides into LAD and Cx The LCA divides almost immediately into the circumflex artery (Cx) and leftanterior descending artery (LAD). The LCA travels between the right ventricle outflow tract anteriorly and the leftatrium posteriorly and divides into LAD and Cx. • Cx with obtuse marginal branch (OM) • LAD with diagonal branches (DB)In 15% of cases a third branch arises in between the LAD and the Cx, known asthe ramus intermedius or intermediate branch. This intermediate branches behavesas a diagonal branch of the Cx.
Left Anterior Descending (LAD)CT image of the LAD in RAO projection The LAD travels in the anterior interventricular groove and continues up to theapex of the heart. The LAD supplies the anterior part of the septum with septal branches and theanterior wall of the left ventricle with diagonal branches. The LAD supplies most of the left ventricle and also the AV-bundle.Mnemonic: Diagonal branches arise from the LAD. The diagonal branches come off the LAD and run laterally to supply the antero-lateral wall of the left ventricle. The first diagonal branch serves as the boundary between the proximal and midportion of the LAD (2). There can be one or more diagonal branches: D1, D2, etc.
Circumflex (Cx) The Cx lies in the left AV groove between the left atrium and left ventricle andsupplies the vessels of the lateral wall of the left ventricle. These vessels are knownas obtuse marginals (M1, M2...), because they supply the lateral margin of the leftventricle and branch off with an obtuse angle. In most cases the Cx ends as anobtuse marginal branch, but 10% of patients have a left dominant circulation inwhich the Cx also supplies the posterior descending artery (PDA).Mnemonic: Marginal branches arise from the Cx and supply the lateral Margin ofthe left ventricle.Right Coronary Artery (RCA)
RCA, LAD and LCx in Anterior projection The right coronary artery arises from the anterior sinus of Valsalva and coursesthrough the right atrioventricular (AV) groove between the right atrium and rightventricle to the inferior part of the septum. In 50-60% the first branch of the RCAis the small conus branch that supplies the right ventricle outflow tract. In 20-30%the conus branch arises directly from the aorta. In 60% a sinus node artery arises assecond branch of the RCA, that runs posteriorly to the SA-node (in 40% itoriginates from the Cx). The next branches are some diagonals that run anteriorly to supply the anteriorwall of the right ventricle. The large acute marginal branch (AM) comes off withan acute angle and runs along the margin of the right ventricle above thediaphragm. The RCA continues in the AV groove posteriorly and gives off abranch to the AV node. In 65% of cases the posterior descending artery (PDA) is abranch of the RCA (right dominant circulation). The PDA supplies the inferiorwall of the left ventricle and inferior part of the septum. LEFT: RCA comes off the right sinus of Valsalva RIGHT: Conus artery comes off directly from the aorta
On the image on the far left we see the most common situation, in which theRCA comes off the right cusp and will provide the conus branch at a lower level(not shown).On the image next to it, we see a conus branch, which comes off directly from theaorta. The large acute marginal branch (AM) supplies the lateral wall of the rightventricle.In this case there is a right dominant circulation, because the posterior descendingartery (PDA) comes off the RCA.Coronary Anomalies Coronary anomalies are uncommon with a prevalence of 1%. Early detectionand evaluation of coronary artery anomalies is essential because of their potentialassociation with myocardial ischemia and sudden death (3). With the increased useof cardiac-CT, we will see these anomalies more frequently.
Coronary anomalies can be differentiated into anomalies of the origin, the courseand termination The illustration in the left upper corner is the most common and clinicallysignificant anomaly. There is an anomalous origin of the LCA from the right sinusof Valsalva and the LCA courses between the aorta and pulmonary artery. Thisintra-arterial course can lead to compression of the LCA (yellow arrows) resultingin myocardial ischemia. The other anomalies in the figure on the left are not hemodynamicallysignificant.
Why are the coronary arteries important?Since coronary arteries deliver blood to the heart muscle, any coronary arterydisorder or disease can have serious implications by reducing the flow of oxygenand nutrients to the heart, which may lead to a heart attack and possibly death.Atherosclerosis (a build-up of plaque in the inner lining of an artery causing it tonarrow or become blocked) is the most common cause of heart disease.SUPERIOR VENA CAVAThe superior vena cava is one of the two main veins bringing de-oxygenated bloodfrom the body to the heart. Veins from the head and upper body feed into thesuperior vena cava, which empties into the right atrium of the heart.INFERIOR VENA CAVAThe inferior vena cava is one of the two main veins bringing de-oxygenated bloodfrom the body to the heart. Veins from the legs and lower torso feed into theinferior vena cava, which empties into the right atrium of the heart.
AORTAThe aorta is the largest single blood vessel in the body. It is approximately thediameter of your thumb. This vessel carries oxygen-rich blood from the leftventricle to the various parts of the body.PULMONARY ARTERYThe pulmonary artery is the vessel transporting de-oxygenated blood from the rightventricle to the lungs. A common misconception is that all arteries carry oxygen-rich blood. It is more appropriate to classify arteries as vessels carrying blood awayfrom the heart.PULMONARY VEINThe pulmonary vein is the vessel transporting oxygen-rich blood from the lungs tothe left atrium. A common misconception is that all veins carry de-oxygenatedblood. It is more appropriate to classify veins as vessels carrying blood to the heart.RIGHT ATRIUM
The right atrium receives de-oxygenated blood from the body through the superiorvena cava (head and upper body) and inferior vena cava (legs and lower torso).The sinoatrial node sends an impulse that causes the cardiac muscle tissue of theatrium to contract in a coordinated, wave-like manner. The tricuspid valve, whichseparates the right atrium from the right ventricle, opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle.RIGHT VENTRICLEThe right ventricle receives de-oxygenated blood as the right atrium contracts. Thepulmonary valve leading into the pulmonary artery is closed, allowing the ventricleto fill with blood. Once the ventricles are full, they contract. As the right ventriclecontracts, the tricuspid valve closes and the pulmonary valve opens. The closure ofthe tricuspid valve prevents blood from backing into the right atrium and theopening of the pulmonary valve allows the blood to flow into the pulmonary arterytoward the lungs.LEFT ATRIUMThe left atrium receives oxygenated blood from the lungs through the pulmonaryvein. As the contraction triggered by the sinoatrial node progresses through theatria, the blood passes through the mitral valve into the left ventricle.
LEFT VENTRICLEThe left ventricle receives oxygenated blood as the left atrium contracts. The bloodpasses through the mitral valve into the left ventricle. The aortic valve leading intothe aorta is closed, allowing the ventricle to fill with blood. Once the ventricles arefull, they contract. As the left ventricle contracts, the mitral valve closes and theaortic valve opens. The closure of the mitral valve prevents blood from backinginto the left atrium and the opening of the aortic valve allows the blood to flow intothe aorta and flow throughout the body.PAPILLARY MUSCLESThe papillary muscles attach to the lower portion of the interior wall of theventricles. They connect to the chordae tendineae, which attach to the tricuspidvalve in the right ventricle and the mitral valve in the left ventricle. The contractionof the papillary muscles opens these valves. When the papillary muscles relax, thevalves close.CHORDAE TENDINEAEThe chordae tendineae are tendons linking the papillary muscles to the tricuspidvalve in the right ventricle and the mitral valve in the left ventricle. As the
papillary muscles contract and relax, the chordae tendineae transmit the resultingincrease and decrease in tension to the respective valves, causing them to open andclose. The chordae tendineae are string-like in appearance and are sometimesreferred to as "heart strings."TRICUSPID VALVEThe tricuspid valve separates the right atrium from the right ventricle. It opens toallow the de-oxygenated blood collected in the right atrium to flow into the rightventricle. It closes as the right ventricle contracts, preventing blood from returningto the right atrium; thereby, forcing it to exit through the pulmonary valve into thepulmonary artery.MITRAL VALUEThe mitral valve separates the left atrium from the left ventricle. It opens to allowthe oxygenated blood collected in the left atrium to flow into the left ventricle. It
closes as the left ventricle contracts, preventing blood from returning to the leftatrium; thereby, forcing it to exit through the aortic valve into the aorta.PULMONARY VALVEThe pulmonary valve separates the right ventricle from the pulmonary artery. Asthe ventricles contract, it opens to allow the de-oxygenated blood collected in theright ventricle to flow to the lungs. It closes as the ventricles relax, preventingblood from returning to the heart.AORTIC VALVEThe aortic valve separates the left ventricle from the aorta. As the ventriclescontract, it opens to allow the oxygenated blood collected in the left ventricle toflow throughout the body. It closes as the ventricles relax, preventing blood fromreturning to the heart.
Get clinical history about the patient which should include present complaints, family history patient’s weight, height, blood investigation reports, ECG, Echo, TMT reports, conventional angiogram reports if done.PREMEDICIATION If heart rate < 65, proceed with the examination If heart rate > 65, to reduce the heart rate. Beta-blockers are prescribed – Metaprolol – EsmololContraindications for beta-blockers Pre-existing bradycardia Bronchial asthma Cardiac failureAllergy to beta blockers 18G Venflon in anticubital vein preferably in right hand.
Ensure proper placement of ECG leadsPRE PROCEDURAL INSTRUCTIONS • Explain the procedure to the patient • Demonstrate Breath-hold instructions.Two important factors that contribute to successful coronary angiogram Stable low Heart rate Good breath holdINDICATIONS Non specific chest pain TMT – Positive Altered ECG signal Post PTCA, Stenting, CABG – follow up Dyspnoea Detection of coronary anomalies
METHODSGATING Imaging must be synchronized to the heartbeat, so that we can acquire dataduring a consistent cardiac phase. We achieve this with ECG gatingECG GATING The ECG waveforms allow us to predict heart motion. We use a percent R-to-Rvalve to control at what cardiac phase image are generated. The goal is to generateimages with the least amount of motion.RETROSPECTIVE GATING Retrospective gating acquires image data and times it to the cardiac cycle duringreconstruction Acquires data from the entire cardiac cycle. It is faster and contiguousacquisition. ECG trace is recorded simultaneously with the scan. Algorithms sort data from different phases by shifting temporal window ofacquired helical projection data. Every position of heart covered at every point incardiac cycle.
Partial scanning and segmented adapted algorithms. Projections of the mid-diastolic phase are selected to reconstruct images from the slow motion diastolephase of the heart.PROSPECTIVE GATING Prospective means that the scan is timed to and triggered from the beats of theheart during the acquisition. Prospective gating is the technique that occurs duringimage acquisition, as opposed to retrospective gating. Redundant radiation occurring during exposure can be substantially reduced withprospective ECG tube current modulation. The technique reduces half the radiationdose to a patient with a heart rate of 60 beats per minute. Image reconstruction with sufficient quality is still possible at anytime within thecardiac cycle. In coronary CT angiography firstly calcium scoring is done followed by thecontrast studyContrast: 1.2-ml/Kg body weight (visipaque)Saline: 30ml.
CONTRAST ADMINISTRATION • Nonionic contrast media • Volume of contrast based on patient weight (Pt. wt x 1.25 ml) • Flow rate – 5 - 5.5ml/sec
CALCIUM SCORING Cardiac calcium scoring uses a special X-ray called a computed Tomography(CT) scan to find the buildup of calcium on the walls of the arteries of the heart(coronary arteries). This test is used to check for heart disease in an early stage andto determine how severe it is. Cardiac calcium scoring is also called coronaryartery calcium scoring. The coronary arteries supply blood to the heart. Normally, the coronary arteriesdo not contain calcium. Calcium in the coronary arteries is another risk factor likehigh cholesterol or blood pressure.
SCAN PROTOCOLPARAMETERS PROSPECTIVE RETROSPECTIVEScan type Axial HelicalGantry rotation time 0.35sec 0.35secDetector coverage 40mm 40mmSlice thickness 0.625mm 0.625mm Based on HRPitch - (0.16 – 0.24)kV 120 120 • Based on BMImA Based on BMI • ECG modulated mA
ECG LEAD PLACEMENTLead of the right arm (RA) should be placed in the sterna notch. Lead of the leftarm (LA) should be placed in the xyphysternum. Lead of the left lower (LL)should be placed in the left costal margin.MECHANICS OF THE STUDYPerformed as routine Chest CTI/V established for contrast injectionECG leads for cardiac gating10-15 seconds breathe hold.
PROCEDURESCANNING PROCEDURE The patient lies supine on the CT scan table and the ECG leads are placed. Theaim is to get a good, regular signal. The patient lies still for almost 5 minutes toestablish and regularize the heart rate. The breath – hold instructions are gonethrough once again with a practice session.POSITIONING:
All the radio opaque materials are removed from the patient’s body. Patient ispositioned supine on the table same as for thorax study. The ECG leads are placedon the patient’s chest. Breathing instructions are given to the patient. Contrastfilled pressure injector is connected to the patient. Contrast filled pressure injectoris connected to the patient’s I/V line.SCANOGRAM: The scanogram is combined as for a chest CT calcium scoring (axial images),from the lower neck to up to just before the diaphragms. For planning the contrastphase from carina to base of the heart.CALCIUM SCORING: CT and in particular, electron-beam CT (EBCT) is the most sensitiveradiographic method to detect coronary artery calcification. The value of EBCTcan be summarized as follows:Absence of Detectable Coronary Artery Calcification EBCT*
• Does not absolutely rule out the presence of atherosclerotic plaque, including unstable plaque • Highly unlikely in the presence of significant luminal obstructive disease • Observation made in the majority of patients who have had both angiographically normal coronary arteries and EBCT scanning • Testing is gender independent • May be consistent with a low risk of a cardiovascular event in the next 2-5 yearsPresence of Detectable Coronary Artery Calcification EBCT* • Confirms the presence of coronary atherosclerotic plaque • The greater the amount of calcification (i.e., calcium area or calcium score), the greater the likelihood of obstructive disease, but there is no one-to-one relation, and findings may not be site specific • Total amount of calcification correlates best with total amount of atherosclerotic plaque, although the true "plaque burden" is underestimated • A high calcium score may be consistent with moderate to high risk of a cardiovascular event within the next 2-5 year
Coronary calcification score • Threshold CT density > 130 HU for pixel areas > 1mm2 • Lesion Score 1 = 130 - 199, 2 = 200 - 299, 3 = 300 - 399, 4 > 400 • Score each region of interest by multiplying the density score and the area • Total coronary calcium score determined by adding up each lesion score for all sequential slicesSMART PREP TECHINQUE
Smart prep is software used in angiogram CT coronary angiography is triggered by the arrival of the main contrast bolus.A pre-scan is taken at the level of aortic root and a region of interest is identified inthe ascending aorta. Repeated scanning is performed at the same level everysecond once contrast injection begins. CTA acquisition is triggered to start as soon as density values in the ascendingaorta reach 2000 HU, at which point patients are instructed to their breath.
ANGIOGRAM PLANNING RANGE: Based on the calcium scoring study, the range is selected. The inferior marginis at the inferior margin of the heart. The superior margin is above LM. Usually weadd at least a three-four heart beat margin superiorly to allow stabilization of theheart rate, after and inspiration is achieved. Then injecting the contrast agentperforms the coronary CT angiogram.
POST PROCESSING TECHINQUESSnap shot burst pulse • Multi Planar Reformation (MPR)/ Curved MPR • Maximum Intensity Projection (MIP) • Volume Rendering (VR) POST-PROCEDURAL CARE • Extravasation
• Allergic Reaction• Hydrate the patient• Reassure patient comfort
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