Dr. Hofmeyer Viljoen, a renowned radiologist and a senior partner in SCP Radiology in Northern suburbs of Cape Town, shares valuable insights on the role of radiology in health screening. Trained as a medical doctor in Bloemfontein and later as a radiologist at Stellenbosch University, he has worked across the globe, providing radiology reports to patients worldwide.
Understanding Radiology Tests
Radiology uses three types of energy: sound energy for ultrasounds, electromagnetic energy for CT scans and x-rays, and strong magnetic fields for MRIs. However, the radiation dose is associated only with x-rays and CT scans. These high-energy photons are shot through the body and absorbed by a detector. Ultrasounds and MRIs are generally very safe, with the only potential risk in MRIs being the strength of the magnetic field if metal objects are accidentally brought into the enclosure.
Radiation dose is measured in Sievert, specifically Milli-Sievert (mSv) for the levels dealt with in radiology. To give a reference, living for one year on this planet exposes you to about 2.4 mSv of radiation, equivalent to what you'll get from a coronary calcium score. An x-ray might expose you to 0.2 mSv, a mammogram to 0.4 mSv. CT scans and angiograms have significantly higher doses but are still relatively low.
The Principle of Radiology
The principle of radiology is to keep the radiation dosage as low as reasonably possible. We won't expose anyone to ionizing radiation if we don't believe there will be a benefit from it. For instance, we wouldn't send someone off the street for a pancreas CT scan without substantial evidence that the benefits outweigh the risks. If someone requests an MRI scan, we might discuss the financial risk versus the benefit, but at least there's no medical risk.
Dexa Scan for Body Composition
One of the common tests we use is the Dexa scan. This is a low dose x-ray system that we sometimes order to gauge the body composition of some of our clients. It helps us determine muscle mass versus visceral fat, something that is often disputed by clients despite what their blood work shows. The Dexa scan is an extremely low dose, about 0.3 mSv, which is about a tenth of a chest x-ray.
The Dexa scanner can also be used to look at the bone density to stratify the risk. For younger patients, we compare you to your age group, while for older patients, postmenopausal women or men after the age of 60, we use a general reference value to determine whether you are on par, osteopenic (one standard deviation below), or osteoporotic (two standard deviations below), which could significantly increase the risk of having a fracture.
Screening for Osteoporosis
As our practice continues to grow, we are starting to see a need for screening for osteoporosis, particularly in our clients aged between 35 and 55. Currently, we use the Dexa scan more for body composition than for osteoporotic type of screening. However, all modern Dexa scanners can measure body composition, and we definitely appreciate its potential in patient care.
Understanding Coronary Arterial Calcium Scoring & CT Angiography
Coronary Arterial Calcium Scoring (CAC) and CT Angiography are two critical diagnostic procedures used to assess the health of the heart. Despite being routine, these procedures are often misunderstood. We delve into what these procedures entail and how they contribute to cardiovascular health management.
Coronary Arterial Calcium Scoring
A CAC scan is a non-invasive diagnostic procedure that measures the amount of calcium in the artery walls. The procedure takes place in a CT scanner, a donut-shaped machine, and the entire process is quick, painless, and uneventful. The radiation dose is about 2 to 3 mSv, equivalent to one year of natural background radiation.
The calcium in the artery walls is graded during the scan, and an algorithm generates a score. This scoring system, known as the Agatston score, was established in the 1980s. There's a linear relationship between the amount of calcium and cardiovascular risk; the more calcium, the higher the risk.
A CAC score is an excellent tool for risk stratification and treatment follow-up, and is particularly useful for asymptomatic patients in their 50s who are resistant to taking statins or other cholesterol-lowering drugs. However, a zero score doesn't mean the absence of plaque formation, it simply means there are no calcifications in the plaque.
CT Angiography
If further diagnostic scrutiny is required, a CT angiography may be performed. This procedure is similar to a CAC scan but involves the injection of an iodine-based contrast agent to outline the heart vessels. Before the procedure, patients are often required to take heart rate-lowering medications (beta blockers) to keep the heart rate as slow as possible inorder to image the heart.
A CT angiography provides a more detailed analysis of the heart vessels, but it also comes with slightly more risk due to the use of contrast. The main risk is an allergic reaction to the contrast agent, which occurs in about one in 4000-5000 patients.
The Significance of Early Screening
CAC scans and CT angiographies are valuable tools in cardiovascular health management, primarily when used for early screening. The idea is not to catch symptoms when they manifest but to track potential issues 20 or 30 years before symptoms like chest pain arise.
Even if a patient's CAC score is under 200, we advise starting preventative treatment; the presence of any calcification indicates that atherosclerosis has started. While some guidelines suggest waiting until a score of 200 to institute statin therapy, we believe in early intervention to manage the disease effectively.
Low Dose CT Screening
Over the past four or five years, low dose CT scans have emerged as an important tool in screening for lung conditions, especially lung cancer. The evidence has shown clear benefits, with the potential to save one life for every 320 scans. This is a much higher benefit than mammography, which requires 1340 scans to save one life.
The criteria for low dose CT scans are clearly defined in the guidelines. Starting at the age of 50 or 55 (depending on the country), the patient needs to have at least 20 pack-years of smoking and should have stopped smoking less than 15 years ago. The annual CT scan continues until the age of 80 or until more than 15 years after smoking cessation.
The CT scan is uncontrasted, similar to a calcium score, and checks for nodules. AI software assists in identifying and measuring each nodule, and any nodule larger than 6mm is followed up, ensuring rapid detection and treatment if necessary.
Mammography
Mammography is an essential part of women's health screening. While the specificity and sensitivity of mammograms may not be on par with CT scans, they are still vital. Every woman can benefit from mammography starting from the age of 40. The international recommendation is an annual mammogram from the age of 40, which reduces mortality by 20 to 30% after the age of 50.
Despite mammography's low specificity, any suspicious findings often lead to a biopsy. The threshold for recommending a biopsy is quite low; if there's a risk of 5 to 10% of a malignancy, a biopsy is usually recommended. This ensures that no potential cancers are missed, even though not all biopsies confirm the presence of cancer.
Prostate MRI
In men, prostate MRIs are a crucial aspect of medical screening. If a patient has a high PSA level, a urologist often requests an MRI for biopsy planning. Prostate MRIs have enhanced doctors' ability to target biopsies, reducing the trauma and uncertainty of blind biopsies.
Whole Body MRI
While whole body MRIs are gaining popularity, there's currently no compelling evidence to support their routine use. Before adopting this practice, we're waiting for guidelines to demonstrate their benefit. The risk of over-investigation and unnecessary biopsies is a valid concern. However, as the technology evolves and guidelines are updated, this could change in the next five years.
The Role of AI in Medical Screening
AI is gaining traction within the field of radiology. It promises to make the screening process faster and more accurate by automating mundane tasks, reducing mistakes, and improving pattern recognition. For instance, AI can count nodules, align scans, and help limit dictation errors. While it's not set to replace human expertise anytime soon, AI can complement and enhance the work of radiologists.
In conclusion, medical screening plays an invaluable role in early disease detection and treatment. From low dose CT scans for lung cancer to mammograms for breast cancer and prostate MRIs for prostate cancer, these procedures have saved countless lives. Moreover, with the integration of AI in screening processes, we can look forward to even more accurate and efficient screenings in the future. It's essential to continue advocating for regular screenings to catch diseases early and increase the chances of successful treatment.
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