Cardiac Calcification Imaging
By: Urmika Balaji, Contributing Writer
Edited by: Fauzia Haque, Editor; Elias Azizi, Editor in Chief
Cardiovascular disease accounts for one in every four deaths in the United States (CDC). The most common cause of cardiovascular disease is atherosclerosis, the narrowing of the arteries due to plaque accumulation, obstructing blood flow and causing blood clots in the blood vessels (Mayo Clinic). Plaque development is inevitable as a person ages. However, certain people can be more prone to cardiovascular disease than others, mostly due to factors related to their lifestyle and family history. Heart attacks, resulting from cardiovascular disease, are often unpredictable, so people prone to cardiovascular disease typically need to be taking medication and must be regularly monitored for symptoms, even before a heart attack is likely. Knowing how soon a heart attack might occur is dependent on how much the plaque is obstructing blood flow in the arteries, which cannot be seen directly by the naked eye. Images of blood vessels and the heart are obtained with the use of radiation and radiation-free imaging technology, such as Angiography, Magnetic Resonance Angiography, Fluoroscopy, and Computerized Tomography Scans. This article will discuss how each of these methods work and the procedures involved.
An angiogram is a procedure that uses static x-ray images to observe and detect blockages in one’s blood vessels (Cleveland Clinic). The patient is sedated and the doctor punctures a blood vessel, typically in the arm, leg, or groin with a long, thin tube called a catheter. The catheter travels through the vessel until it reaches the desired area of examination. Then, an intravenous dye, typically consisting of iodine, will be injected into the vessel to observe the flow of blood in the blood vessels in the area, and an x-ray is used to take a static image. A lack of visibility of the dye in a blood vessel indicates a plaque blockage in the blood vessel (Cleveland Clinic). An angiography is often coupled with a fluoroscopy, which helps guide the catheter into the area of examination. Due to the insertion of a catheter, other procedures, such as angioplasty—balloons or stents inserted to prevent narrowing of arteries—can also be provided to the patient. The radiation exposure of an angiogram is typically 500 chest x-rays (Vijayalakshmi). One chest x-ray is equivalent to the amount of normal radiation exposure in two and half days, so a patient is exposed to more than three years worth of normal radiation in just one angiogram.
Fluoroscopy is an imaging method that uses continuous x-ray beams to generate a real-time moving image of a body part (John Hopkins Medicine). A patient undergoing a fluoroscopy is often injected with intravenous dye, which will allow the blood vessels to appear more clearly as the dye is circulated through the blood (URMC). When it is coupled with more invasive cardiac procedures, such as an angioplasty (balloon/stenting), fluoroscopy will be performed while a patient is sedated or under anesthesia. Fluoroscopy is often used to guide the placement of catheters: thin, flexible tubes that can be used to insert stents or balloons against the artery wall to prevent the further narrowing of arteries due to plaque. The real-time imaging also allows for medical professionals to observe the circulation of blood, revealing any obstructions of blood flow due to calcified or noncalcified plaque. The radiation exposure of fluoroscopy can range from 250 to 3,500 chest x-rays (WebMD). As a result, a patient can be exposed to anywhere from 1.7 years to 24 years worth of normal radiation within one fluoroscopy. The radiation exposure is dependent on the type of procedure, length of exposure, and the quality of the imaging (FDA).
Magnetic Resonance Angiography (MRA)
Unlike an angiogram, an MRA does not use x-ray radiation to create images of the body, and it is much less invasive because it does not require a catheter. Instead, it uses radio waves and a magnetic field to generate a computerized image of the blood vessels (John Hopkins Medicine). Before the patient enters the MRI scanner, they must remove all metal objects on clothing or the body because metal can interfere with the magnetic field creating the image. While the patient is in the scanner, an intravenous dye is injected into the blood vessels to appear clearly in the image.
Source: Advanced Health Education Center Catheter inside a blood vessel
Computerized Tomography (CT) Scan (1971)
A CT Scan is an x-ray procedure that produces cross sectional images of the body with computer processing (Beckerman). A CT scan utilizes a motorized x-ray source that releases x-ray beams as it rotates around the body. X-ray detectors, opposite to the source, transmit the x-rays to a computer, which then generates an image of the cross-section of the body taken. During the procedure, a patient will be asked to hold their breath for 20 to 30 seconds, which will allow for a stable image to be produced (UMMS). Unlike an angiogram, it does not require the insertion of a catheter into the blood, making it a less invasive procedure. The CT Scan is a common device used for detecting plaque in blood vessels. The typical radiation exposure for a CT Scan is about 484 chest X-rays, or 3.3 years of normal radiation exposure.
CT Scan revealing calcified lesion in the heart. CT Scan Procedure
Calcium-score Screening Heart Scan
The Coronary Artery Calcium Scoring (CACS) quantifies the calcification detected by a CT Scan. Because intravenous dye is not used, non-calcified plaque is not taken into account in the scan. It is usually used as a general marker of the severity of atherosclerosis in a patient, correlated to their risk of death in the next decade. The score is calculated by adding the products of the area and density of each lesion of calcification. The scores are classified in the following way:
CAC=0: very low risk of death (< 1% at 10 years)
CAC=1-100: low risk of death (< 10% at 10 years)
CAC=101-400: intermediate risk of death (10-20% at 10 years)
CAC=101-400 and >75th percentile for age, sex, and ethnicity: moderately high risk of death (15-20% at 10 years)
CAC>400: high risk of death (>20% at 10 years)
Although the classification is associated with the mortality of the patient, CACS cannot predict exactly when a heart attack will occur.
CTA (Coronary CT Angiography)
CTA is a quick, non-invasive imaging method that provides a high resolution, 3-dimensional view of the heart and blood vessels to detect plaque build-up in coronary arteries (Mayo Clinic). Unlike a standard angiogram, a CTA does not require the insertion of catheters. Using different cross-sections of the area of examination, x-rays pass through the body and are picked up by detectors, which the computer can use to synthesize a 3-dimensional image. The 3-dimensional imaging aids in classifying the plaque as calcified or noncalcified plaque. A CTA Scan exposes a patient to the radiation of 600 chest x-rays, or about 4 years of normal radiation exposure (Duke Radiology). During the procedure, the patient is injected with intravenous dye in order for the area of examination to appear more clearly. It is also a quick procedure, typically lasting only 10 minutes.
CTA Scan of the heart
Source: Cleveland Clinic
The angiogram, magnetic resonance imaging, and computerized tomography scan methods yield success in diagnosing several heart conditions, such as atherosclerosis, coronary artery disease, arterial stenosis, and many others. However, issues with these methods arise from their level of radiation exposure. Many patients taking regular scans can be exposed to significantly large amounts of radiation in just one procedure, leading to risks of many other types of cancers. Because heart issues can risk unpredictable death, many heart patients are scanned periodically over several decades of their lives, so they are especially exposed to risks of other cancers, which can be extremely costly to both the patients and the hospitals. Thus, the goal of new imaging technology has been to reduce radiation exposure. One of these methods is the Electron-Beam Computed Tomography (EBCT), which uses a singular x-ray tube that partially surrounds the examination area and generates an image ten times faster than a CT Scan (Dutta). The quick procedure reduces the radiation exposure of a traditional CT Scan by 6 to 10 fold (Dutta). With the increasing prevalence of cardiovascular disease around the world, such methods will need to be implemented to reduce patients’ risks of developing further complications.