Technological advances increasingly mean that doctors are able to see and assess the function and structure of our organs without having to cut our bodies open or insert instruments into us.
Imaging methods like X-rays and ultrasound are familiar to us all, with many of us having undergone at least a chest X-ray (as part of a health check-up before being hired) or an abdominal ultrasound (for pregnant women).
Some of us with medical concerns or conditions might have undergone more advanced imaging like CT (computed tomography) scans, PET (positron emission tomography) scans and MRI (magnetic resonance imaging).
According to National Heart Institute (commonly known by its Malay acronym, IJN) consultant cardiologist Datuk Dr Ahmad Khairuddin Mohamed Yusof, CT scans are actually multiple X-ray images taken from various different angles.
“From there, we reconstruct images so we can see the anatomical structures in the patient’s body,” explains the specialist in cardiovascular imaging and interventional cardiology.
The multiple X-ray images are combined into a number of cross-sectional images – also known as “slices”– of the targeted body part via a computer programme.
“On the other hand, the PET scan is the mechanism of seeing the function of the organ by introducing a radioisotope into the patient’s body. Once the radioisotope gets into the patient’s body, it will decay, and the decaying process will produce gamma-radiation,” he says.
“This radiation will be detected by special detectors, which will produce and reconstruct images via multiple complex algorithms, and from there, we can see how the organ functions as a whole.”
For example, the radioisotope fluorine-18 is commonly combined with glucose to form fluorodeoxyglucose, a common tracer for PET scans.
As a form of glucose, fluorodeoxyglucose is taken up by cells as part of their energy-producing process, thus enabling its concentration in various tissues and organs to be measured.
Cancer cells, for example, tend to use far more glucose than ordinary cells, making PET scans useful for identifying malignant tumours.
There are also PET-CT scan machines that combine both these methods into one piece of equipment. This allows for more accurate imaging as the anatomical images from the CT scan and the functional images from the PET scan, which are done consecutively in the same session, can be combined into a precise picture of the targeted organ.
IJN Imaging Centre manager Norizam Mois explains: “This advanced hybrid imaging modality or scanner has been shown to be superior to conventional imaging in terms of diagnostic accuracy, efficiency and lower dose.
“The primary purpose of using this scanner is to improve the evaluation of the functions of the heart and associated thoracic oncology.”
She adds: “IJN not only receives referrals for cardiovascular disease, but also for cases of thoracic surgery involving tumours, as well as other cancerous areas. We also offer PET-CT services to other hospitals for diagnostic evaluation.”
One of the main differences between PET scans and CT scans, she says, is that the PET scan reveals metabolic changes in an organ or tissue earlier at cellular level. “So, the use of the PET-CT scanner with the 128 slices, will help us manage these patients more effectively.”
Norizam adds: “IJN is also committed to establish an imaging centre that offers a comprehensive range of non-invasive diagnostic imaging for a wide scope of medical needs.”
Advantages of PET-CT
“We handle a lot of patients with heart disease, so PET-CT is one way of assessing the function of the heart,” says Dr Ahmad.
“Although we do have SPECT, or single-photon emission computed tomography, which is another method of assessing the function of the heart, we consider PET-CT another newer method with advantages over the older one.”
One advantage is reduced radiation exposure for the patient, as the radioisotope dose profile for PET-CT scans are lower than those for SPECT.
Another is the ability to measure coronary flow reserve, which is the maximum increase in blood flow through the coronary arteries that supply the heart, above the normal resting volume.
This is usually done for patients suspected of having at least 50% stenosis, or narrowing, of one or more of their coronary arteries to see if they require treatment.
“By introducing a nitrogen-13–ammonia or rubidium-82 tracer, which are the special radioisotopes for this PET-CT scan, into the patient, we will be able to assess the coronary blood flow during rest and during stress.
“With these two pieces of information, we will be able to calculate the ratio and come up with the coronary flow reserve of this patient.”
Previously, the patient would have to undergo coronary angiogram, which requires inserting a catheter into a blood vessel in the groin or arm all the way up to the heart. If the cardiologist decides that there is a narrowing of 70% or more based on the angiogram, treatment will proceed.
If it is less than 70%, the patient would need to go for another test, a dopamine-stress test, to see if there is a significant disruption in coronary blood flow during stress.
“However, once we have this PET-CT scanner, this issue can be addressed by asking the patient to undergo this scan. From there, we can immediately decide whether the patient needs ballooning or angioplasty,” he says.
The third advantage is being able to assess the viability and functionality of heart muscle. Says Dr Ahmad: “Let’s say the heart muscle is weak, and we want to know if the weakness is due to poor blood supply, or damaged or dead heart muscle.”
He explains that when the heart muscle has poor blood supply, it adapts by changing its metabolic activity. “Instead of using fat as the source of energy, it will use glucose as the source of energy. But this glucose is limited in supply, so the ability of the heart to pump is reduced,” he says.
Therefore, when the tracer fluorodeoxyglucose is introduced, it would be avidly taken up by the poorly-supplied heart muscle, which can be seen on the PET-CT images. If the muscle is damaged or dead, there would be no difference in the fluorodeoxyglucose levels.
This helps the cardiologist to decide on whether or not to treat any narrowed coronary arteries – yes, if the problem is poor blood supply, and no, if the heart muscle is already dead or damaged.
Upgraded CT scan
IJN recently acquired a brand new PET-CT scanner. In addition, the institute upgraded one of its CT scanners, which now provides 512 slices, compared to the 64 slices of the older machines.
“This CT scan has less radiation exposure to the patient,” says Dr Ahmad. “The detector is bigger, so we will be able to image the heart at high quality without exposing the patient to high radiation, as compared to the old CT scanner.”
Due to the faster image capture, patients need only hold their breath for one to two seconds, compared to around 12 seconds for the older one. Most anxious patients can also skip a beta-blocker drug to slow down their heart rate, as this scanner can capture high-quality images in a heartbeat.
“This CT scan also has the capability of doing fractional flow reserve, which is a special technology not available in our previous CT scanner,” says Dr Ahmad.
Fractional flow reserve is the blood flow through a specific segment of the coronary artery. It is used to determine whether or not the narrowing of the artery results in a disruption of blood flow through it, and thus, whether or not it needs to be treated.
He added that the upgraded CT scanner can also function similarly to a cardiac MRI where it can detect stress-induced ischaemia, i.e. inadequate blood supply to the heart during physical stress. It does this by taking images while the patient is at rest and under drug-induced stress.
“So, in the future, we can offer this CT scan to those patients who are not able to get into a cardiac MRI scanner because of claustrophobia – fear of a closed environment,” says Dr Ahmad.
He explains that for an MRI, the patient’s body is fully enclosed by the machine, while only half of their body is enclosed for a CT scan.
“We, being the National Heart Institute, are at the forefront of technology, and cardiac imaging is the area where the advancements are,” says IJN CEO Datuk Seri Dr Mohd Azhari Yakub.
“We are investing in this technology to provide patients non-invasive cardiac imaging, which can give us a lot of information without the patient having to go for an invasive technique.”
He added that they have also invested in their people by sending two doctors and four medical technicians overseas to be trained and certified in reading the PET-CT images and handling the machine respectively. While PET-CT scans are available in Malaysia, they are focused in the area of oncology, or cancer.
“Here we are providing not only screening or investigation for oncology patients, but also sub-specialising in cardiac PET-CT,” says the senior consultant cardiothoracic surgeon.
The two new and upgraded machines were sponsored by Permodalan Nasional Bhd (PNB) as part of their corporate social responsibility (CSR) efforts. “With their contribution, we are able to provide a very competitive fee for the imaging, which will benefit the patients,” says Dr Azhari.
He adds that IJN will be charging a maximum of RM3,000 for oncology screening by PET-CT. PET-CT cardiac imaging will cost slightly more than RM3,000 due to the more expensive radioisotope they have to use, he says.
He adds that IJN will be reducing the cost of CT scans in their centre with the addition of the two new machines, as they now have three CT-capable machines in total. “This is all part of the vision of IJN: to provide high-quality care, which is affordable to the ordinary Malaysian,” he says.