Medically reviewed by Prof. Dr. Aamer Nadeem Chaudhary, M.B.B.S., D.M.R.D., F.C.P.S. (Diagnostic Radiology), Consultant, Al-Nasar Lab & Diagnostic Centre. Updated August 2026.
Quick answer: The slice count of a CT scanner is how many image slices it captures in a single rotation. A 640 slice scanner covers up to 16 cm of the body in one rotation, which means far faster scans, thinner and sharper images, less blurring from movement, and often a lower radiation dose than older 16 or 64 slice machines.
Book a CT scan: call 0300 0341944 or request an appointment here. See our 640 slice CT scan page for details and pricing.
What does 640 slice mean on a CT scanner?
A CT scanner works by rotating an X-ray tube around you while detectors on the opposite side record the beam. Each rotation produces a set of thin cross sectional images, called slices, which a computer stacks into a detailed picture of the body.
The slice number refers to how many of those images the detector array captures per rotation. A 16 slice machine captures 16. A 640 slice machine captures 640. More slices means more of the body is covered in a single pass, and each slice can be thinner.
Does a higher slice count give a better scan?
For many routine scans, a 64 or 128 slice machine produces perfectly diagnostic images. The difference becomes significant when the body part is moving, when the patient cannot hold still, or when very fine detail is needed. That is where a 640 slice scanner changes the result rather than just the comfort.
| Feature | Standard scanners (16 to 64 slice) | 640 slice scanner |
|---|---|---|
| Coverage per rotation | Roughly 2 to 4 cm | Up to 16 cm |
| Heart imaging | Multiple rotations, images stitched across several heartbeats | Whole heart in a single rotation, often one heartbeat |
| Breath hold required | Longer | Very short, sometimes none |
| Movement blurring | More likely | Greatly reduced |
| Suitability for children | Sedation more often needed | Speed often avoids sedation |
| Radiation dose | Higher for equivalent coverage | Lower for equivalent coverage |
Which scans benefit most from a 640 slice CT?
Cardiac CT and coronary angiography. The heart never stops moving, so imaging it is the hardest job a CT scanner faces. A 640 slice machine can capture the entire heart within a single heartbeat, which removes the motion blur that forces repeat scans on slower machines. Read more about CT coronary angiography in Lahore.
Children and anxious patients. A scan that finishes in seconds rather than minutes often removes the need for sedation, which is safer and far less distressing for a child and family.
Stroke and trauma. In an emergency, speed is clinical value. Faster imaging means faster decisions about treatment.
Chest, abdomen and vascular studies. Wide coverage in one breath hold produces cleaner images in patients who are breathless or in pain.
Is a 640 slice CT scan safe?
Yes. CT uses X-rays, so there is a radiation dose involved, but a higher slice count generally reduces that dose rather than increasing it, because the machine covers the required area in far less time. Modern scanners also use dose reduction software that adjusts output to your body size.
Tell your radiographer if you are, or might be, pregnant. As with any scan, a CT is performed when the diagnostic benefit outweighs the small radiation risk, which is a decision your doctor makes with you.
How should you prepare for a CT scan?
- If contrast dye is being used, you may be asked to fast for about four hours beforehand
- Tell the team about kidney problems, diabetes medication, asthma, or any previous reaction to contrast
- Wear comfortable clothing without metal, and remove jewellery
- Bring any previous scans and reports, which help the radiologist compare
- Most scans take only a few minutes once you are positioned
What is the difference between a CT scan and a city scan?
They are the same thing. City scan is simply how CT scan is commonly pronounced and written in Pakistan. If your prescription says city scan, a CT scan is what has been requested.
CT scanning at Al-Nasar Lab
Al-Nasar Lab & Diagnostic Centre operates advanced CT technology at its main Johar Town campus, which is the full service diagnostic site offering CT, MRI, ultrasound, X-ray and nuclear medicine under one roof. We also run 128 slice CT and provide reporting by qualified consultant radiologists.
Explore all CT scan services in Lahore, find your nearest branch, or call 0300 0341944 to book.
Frequently Asked Questions
How long does a 640 slice CT scan take?
The scan itself usually takes seconds to a couple of minutes. Including preparation, positioning and any contrast injection, expect to be at the centre for roughly 20 to 30 minutes.
Is a 640 slice CT better than an MRI?
They answer different questions. CT is faster and better for bone, lung, bleeding and emergency assessment. MRI gives superior soft tissue detail with no radiation. Your doctor chooses based on what needs to be seen, not on which machine is newer.
Do I need contrast dye for my CT scan?
It depends on what is being examined. Contrast highlights blood vessels and certain tissues, so it is standard for angiography and many abdominal studies, and unnecessary for others such as most bone or lung scans.
Can I have a CT scan if I have kidney problems?
Often yes, but tell the team beforehand. If contrast is required, a recent kidney function test may be requested and precautions taken, or a different scan may be recommended.
How soon will I get my CT report?
Al-Nasar Lab provides same day digital reporting for most CT studies, with complex cases reported as soon as consultant review is complete.
This article is for general information and is not a substitute for medical advice. Please discuss your scan and results with a qualified doctor.
