Cardiovascular Imaging

ROLE OF ULTRASOUND SCAN,CT,MRI, & FLUOROSCOPY Mkhululi Ndlovu SRA(NUST)

ULTRASOUND SCANProvides a real-time view as either 2D slices or 3D reconstructions,with no radiation,making it the investigation of choice for a number of conditions.

ULTRASOUND SCANUses high-frequency sound waves to view soft tissues such as muscles and internal organs. Because ultrasound images are captured in real-time, they can show movement of the body's internal organs as well as blood flowing through blood vessels.

ULTRASOUND SCANIn an ultrasound exam, a hand-held transducer is placed against the skin. The transducer sends out high frequency sound waves that reflect off of body structures. The returning sound waves, or echoes, are displayed as an image on a monitor.

ULTRASOUND SCANThe image is based on the frequency and strength (amplitude) of the sound signal and the time it takes to return from the patient to the transducer.

ULTRASOUND SCAN

Its applications include echocardiography,with special applications such as transesophageal echocardiography[TEE],and Doppler ultrasound.

ULTRASOUND SCAN

Another special feature is Doppler fetal heart rate monitor,which is a hand held transducer used to listen to the fetal heart beat.

ULTRASOUND SCANEcho is a non-invasive and more accurate method for the quantification of left ventricular ejection fraction[ie,measurement of the amount of blood ejected from the left ventricle with systolic contraction].

ULTRASOUND SCANThis helps in ruling out systolic dysfunction.It may be used to calculate cardiac chamber size and wall thickness,and to diagnose the presence of valvular dysfunction and pericardial effusion.

ULTRASOUND SCANOther measurements such as stroke volume and cardiac output may be calculated with Echo.Echo will also diagnose complications of myocardial infarction[MI] such as papillary muscle rupture,ventricular septal defect,left-ventricular aneurysm and pericardial effusion.

ULTRASOUND SCANIt is the usual imaging test,together with chest x-ray,in the assessment of congestive heart failure.Echo also allows direct visualisation of cardiac anatomy accompanied by Doppler analysis of flow rates through valves and septal defects.

ULTRASOUND SCANIn special cases,ultrasound contrast agents may be injected to enhance the Echo.This may be mainly applied to visualise small intracardiac shunts such as atrial septal defect. Colour Doppler helps in the identification of septal defects and quantification of gradients across stenotic valves.

ULTRASOUND SCANDoppler US also helps in differentiating focal stenosis from diffuse disease and occlusion. Aneurysms, pseudoaneurysms and arteriovenous malformations[AVM] are well seen in Doppler US ,and is also useful for post operative graft surveillance.

ULTRASOUND SCANIn the case of abdominal aortic aneurysm,USS may be useful where CT is unaccessible or for follow-up measurement of a known asymptomatic aneurysm.USS provides the advantages of no ionising radiation, non-invasiveness,quick,and relatively cheap.However,it is operator dependent.

CT SCANUses conventional X-ray beams emanating from different directions through the patient,then reconstructed into a single image with the use of a computer.

CT SCAN

The resulting image(axial cut) shows cross-sectional views free from superposition.

CT SCAN

Cardiac CT(Contrast enhanced or non-contrast enhanced) is useful to diagnose heart disease.It helps to visualise heart anatomy,coronary circulation,and great vessels(i.e aorta,pulmonary arteries and veins).

CT SCAN

Several types are used that include total body heart scans(TBCT),calcium-score screening heart scans,and coronary CT angiography(CTA).

CT SCANThe screening(non-contrast enhanced) is done to detect calcium deposits found in atherosclerotic plaque in the coronary arteries,before symptoms develop.This helps in preventing future heart problems,coronary artery disease and in reducing their risk.

CT SCAN

CTA is a non-invasive and contrast enhanced(iodine is used) heart imaging test,useful to determine if either fatty or calcium deposits(plaques) have built up in the coronary arteries

CT SCAN CTA can determine coronary artery stenosis. It can non-invasively detect the soft plaque or fatty matter in the coronary artery walls that has not yet hardened but may lead to future heart problems without lifestyle changes or medical treatment.

CT SCAN

CTA can determine whether symptoms of chest pain may be caused by coronary blockage,esp in persons that may be at risk;with a family history of cardiac events, diabetes, high BP, smokers,and those with elevated cholesterol

CT SCAN

CTA can also be used for assessment of coronary artery bypass grafts and stent patency.

CT SCAN

CT scan also plays a crucial role in mapping of the anatomy of the left atrium and pulmonary veins prior to radiofrequency catheter ablation for atrial fibrilllation.

MRI SCAN

Uses strong magnetic fields and radiofrequency waves to produce a signal that can be reconstructed into an image slice.

MRI SCAN

It results in production of cross-sectional images of organs and internal structures in the body.It does not use ionising radiation.However,the strong magnetic field used is unsafe for metal substances such as pacemakers.

MRI SCANBecause the signal detected by an MRI machine varies depending on the water content and local magnetic properties of a particular area of the body, different tissues or substances can be distinguished from one another in the study image.

MRI SCANThe term cardiac MR(CMR) is used because of its application in investigation of cardiac disease,described below.CMR is useful in evaluation of cardiac function.

MRI SCANIn this case,it enables calculation of ejection fraction,assessment of myocardial mass ,and regional wall motion where echocardiography may be equivocal.

MRI SCANIt also helps in determination of congenital heart disease, complementary to echocardiography

MRI SCANCMR is especially useful in assessing cardiac anatomy,to help rule out cardiomyopathy,left ventricular aneurysm,where echo is difficult/equivocal.Its increasing role is now ruling out myocardial viability(weakened myocardium).

MRI SCANAn infarct scan may be performed and the contrast media accumulates in the infarcted myocardium,allowing direct visualisation on a delayed scan.

MRI SCANCMR is also useful in ruling out great vessel disease,such as aortic dissection and coarctation.It can also assess cardiac masses and rule out pericardial disease.

MRI SCANMRI provides the advantages of no ionising radiation,no iodinated contrast media,good soft tissue differentiation,multiplanar imaging,and no interference from bone or air.

MRI SCANHowever,its drawbacks include relatively long scan times,general anaesthetic required for infants and young children,other contraindications including cardiac pacemakers.

FLOUROSCOPYProvides real time X-ray imaging,useful for guiding a variety of diagnostic and interventional procedures.

FLOUROSCOPYIn angiography(procedure that uses catheterisation),contrast media is injected through the catheter and images are obtained using the digital fluoroscopy.

FLOUROSCOPY

The entire coronary and artery system is visualized. Stenosis (blockages/narrowing) inside blood vessels which inhibits blood flow and causing pain can be assessed.

FLOUROSCOPY

For all structures,except the heart,images are taken using the technique,Digital Subtraction Angiography(DSA).

FLOUROSCOPY

DSA is achieved through obtaining a pre-contrast image and then subtracting the background after injection of a contrast media.This allows the column of contrast in the angiogram to be displayed without interference of the background.

FLOUROSCOPY

Thus fluoroscopy is useful in “road mapping” through real-time catheter guidance with a contrast background.

FLOUROSCOPY

This is achieved through digitally subtracting the initial non-contrast background, then contrast is injected into the vessel of interest and a new combined image of the contrast injection is superimposed on the real-time fluoroscopic image.

FLOUROSCOPY

Besides cardiac catheterisation[which helps to evaluate the presence of coronary blockages though assessment of blood flow through the conorary arteries],fluoroscopy is also useful in pacemaker Insertion.In this case,a central vein (ie subclavian, internal jugular, or axillary vein) is accessed via a percutaneous approach.

FLOUROSCOPY

A pacemaker can be implanted into the chambers of the heart under flouroscopic guidance.

FLOUROSCOPY

During the procedure,it helps in guiding the passage for guidewires,leads and sheaths.This is done under pulsed fluoroscopy.However,in some patients this may be technically difficult because skeletal landmarks are deviated. Hence,in this case,an initial brief fluoroscopic examination will be required.

FLOUROSCOPYThis will greatly reduce the time and complications associated with obtaining the access.Preoperative fluoroscopy may also be necessary for the arteriography of the aorta and great vessels to determine precise anatomical relations when proximal landing zone of the stent graft cannot be determined by non-invasive imaging.The major drawback of fluoroscopy is the high radiation dose to the patient.

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