128 slice CT Volume Multi-detector CT Scan
A regular CT has a tube rotation speed of 1 or 0.75 seconds. Volume CT has tube rotation speed of 350ms, i.e., approximately 3 rotations per second. Moreover, Volume CT has wide detector coverage of 40mm. This allows extremely fast and comprehensive scans of the body, such that routine chest and abdomen sequences can be completed in 3 - 5 seconds. Instead of slices, volume CT collects data in volume, and that is the reason why it is called Volume CT.
With such fast scanner, it is possible to "Freeze" the heart. After gating with the ECGs, it is possible to scan the heart in 5 seconds and to extract information about the coronary arteries and cardiac function from the dataset.
3 hours fasting is needed before the procedure. Patient's heart rate is stabilised with a betablocker. All old cardiac-related information from the patient is helpful. Once the heart rate is stabilised, a vein is cannulated. Breathing instructions are given so that the patient can hold his/her breath for around 4 to 7 seconds. A calcium scoring study is performed, and a dye is injected for the angiogram study to be performed. The angiogram time is 4 to 6 seconds. The entire procedure takes between 15 to 30 minutes depending on the heart rate.
The following three parameters are studied as part of the procedure:
- Calcium scoring
- Coronary artery assessment
- Functional assessment (wall motion and ejection fraction)
- Patients at high risk for developing coronary artery disease (high triglycerides, family history, smoking)
- Follow-up of known mild to moderate untreated disease
- Post-bypass assessment
However, in patients with ectopic beats and an irregular rhythm, it is difficult to perform a cardiac CT. X-rays involve radiation (though there are practically no dangers), and hence, should be done in pregnant women only after weighing all the risks and benefits. Cardiac CT cannot be performed on unconscious patients.
The majority of patients will be injected with a "dye" which enhances the ability of CT scans to pick up abnormalities. This is routine. Only a non-ionic dye (the safest) is used. However, 0.5 percent of patients may get nausea and redness of the skin. Though severe reactions are known, these are very rare and uncommon. Please inform the doctor, nurse or the receptionist, if you are at high risk for "dye" injection, i.e., if you have a history of drug reactions, bronchial asthma, cardiac or kidney disease, etc.
While visiting Amala Cardiac Centre, please get all old X-rays, sonography, CT and MR films along with other papers, operative notes, discharge cards, etc. relevant to the case. There should, preferably be an accompanying friend or relative.
- Cardiac CT for coronary arteries is essentially a screening tool.
- The negative predictive value is greater than 98%. That means that when the study is normal, it is almost definite that there is no coronary artery disease.
- If contrast is seen distal, to a stenotic lesion, occlusion cannot be excluded, since there is no flow information.
- It may not be possible to accurately assess instent lumens in stents < 3 mm in diameter.
- Soft plaques are best seen on CT and may not be seen on a conventional coronary angiogram.
- The functional information tends to be under-estimated by 5-10% as compared to MRI.