New Cardiac Imaging
Computed Tomography scanners, or CT scanners, first appeared in the 1970s. The basic principle is similar to an x-ray scanner. There is a source and detector, with the source sending x-rays through the patient to the detector. The x-rays passing through to the detector create a shadow, which creates an image. Unlike flat, black and white x-rays, CT scans are often in color with a 3 dimensional appearance.
“The real innovation with the CT is that you have a source and detector that are moving around the patient, shining x-rays on multiple different angles,” explains Dr. Sridhar Charagundla, a Cardiovascular Imaging Radiologist with the University Of Pennsylvania Hospital.
“Instead of creating a 2-D image you can create a 3-D image. “
Advantages
Within the last 10 years, the innovation has been multiple detector (or “slice”) CT scanning. Multiple detectors allows for more efficient x-ray distribution and collection.
“The dramatic improvement is speed,” notes Dr. Charagundla. “In the first generation of CT Scanners it would have taken an hour to do a study that study today takes 15 seconds.”
Faster studies are more resistant to problems, such as patient movement or instability.
“If you take a picture of a moving object, the faster the shutter speed – the less blurry the image,” explains Dr. Charagundla. “The heart is always beating, and the patient is breathing. This is two kinds of motion that are very difficult to control for. It’s hard to get everybody to hold there breadth for 25 seconds, especially someone with heart disease. It might not seem a big deal from the outset, but dropping a few seconds can improve the study.”
Patients undergoing most cardiac imaging are given an injection of contrast, x-ray dye. The contrast is injected into the patient’s vein, allowing for crisp and clear images to be taken while the material circulates through the blood stream. But the non-toxic contrast quickly dissipates, so quicker imaging produces the best scans. This is true for both cardiac imaging and vascular imaging.
Innovation
The latest model in multi-slice CT scanning is the 64 slice scanner, one of which is owned by the University of Pennsylvania Hospital. With the 64 slice scanner, resolution and speed are unbeatable. 64 slice scanning is now the preferred imaging in both cardiac and vascular imaging, while cardiac imaging is driving the development of this technology.
“Cardiac imaging has made incredible leaps, and our vascular imaging is off-the-map having gone from 16 to 64,” says Dr. Charagundla.
In the days before cardiac CT, the only way to image the arteries was to insert a catheter, inject contrast, and take x-rays. With CT, you’re only inserting in tiny IV, essentially non-invasive. While catheter technology is known to be a safe technique, there are still a known very small percentage of patients who might have complications. With CT scanning, the complication percentage decreases since the patient is barely touched.
Now 64 slice imaging is comparable with cardiac catheterization when detecting lesions or narrowing of the coronary arteries. While catheterization is still the gold standard, data indicates that 64 slice CT is comparable. 64 slice CT also indicates structure of the walls in a coronary artery, information that catheterization will not. Data on vascular walls can help in diagnostic assessment tremendously.
“There are 5 to 10 institutions including the University of Pennsylvania doing these types of studies, there’s no clear leader. But from a local stand point, we are the only game in town.”
University of Pennsylvania is now doing 5 to 8 patients a day for cardiac imaging. Penn is getting a second and more advanced scanner to help with the increase in volume.
Risks and Concerns ?
Some in the medical field feel cardiac multi-slice CT carries very real risks since it exposes the subject to the equivalent of 500 chest x -rays in terms of radiation. The relationship of radiation exposure to increased risk in cancer has yet to be definitively explored.
“Any time there is new technology it has to be met with some skepticism.” Dr. Chargundla states, “Doing a cardiac 64 slice CT does involve more x-rays, but a comparable dose to a cardiac catheterization. In terms of a risk to patients, the increased risk of the x-rays is outweighed by the improved results, and is balanced by the decreased complications. The FDA has signed off on this. It’s not a study you want to do every week or every month, but once or twice in a patient’s lifetime.”
Another concern is that many multi-slice CT technicians are trained cardiologist as opposed to radiologists. The positive and negative predictive values of the scan are calculated on the basis of a knowledgeable staff.
“CT is scanning is what radiologists do. The key point here is that people need to get adequately trained. Radiologists have the training in place, and the proper skill sets.
“But I’m a radiologist, so I am biased,” laughs Dr. Chargundla.”The key is training, it’s not magic, and as long as you’re properly trained it is fine.”
