How a CT scan works
A CT scan in Dehradun — computed tomography — uses X-rays to build cross-sectional images of the body. An X-ray tube rotates rapidly around you inside the gantry while an opposing arc of detectors records how much radiation passes through from every angle. A reconstruction algorithm then converts those thousands of projections into a stack of slices, which can be reformatted into any plane or rendered in three dimensions.
The practical consequences of that design are what make CT so useful. Acquisition is extraordinarily fast — a whole chest can be captured in a single breath-hold of a few seconds — and because the images are built from X-ray attenuation, dense structures like bone and fresh blood appear with excellent contrast. That combination of speed and bone sensitivity is why CT is the emergency department's default and why a suspected head injury or acute stroke goes to CT first, not MRI.
CT or MRI — a straight comparison
Patients frequently ask which is "better". Neither is. They answer different questions, and a good referral picks the one that matches yours.
| Factor | CT Scan | MRI Scan |
|---|---|---|
| Physics | X-rays | Magnetic field and radio waves |
| Radiation | Yes | None |
| Acquisition time | Seconds | 20–60 minutes |
| Bone detail | Excellent | Limited |
| Acute bleeding | Excellent | Good but slower |
| Soft tissue contrast | Moderate | Excellent |
| Lung parenchyma | Excellent | Poor |
| Discs, cord, ligaments | Limited | Excellent |
| Kidney stones | Gold standard | Poor |
| Early stroke | Often normal in first hours | Positive within minutes on DWI |
| Metal implants | Streak artefact but usable | Significant distortion |
| Claustrophobia | Short, open ring — rarely an issue | Long tunnel — can be difficult |
The short version
Bone, blood, stones, lungs and emergencies go to CT. Brain detail, spinal cord, discs, ligaments, cartilage and anything needing soft-tissue contrast go to MRI. If you are claustrophobic or have a device that rules out MRI, CT is frequently a workable alternative — ask us and we will tell you honestly whether it answers the same question.
The CT studies we perform
CT Head / Brain
The most frequently performed CT anywhere. Plain CT head takes seconds and reliably detects acute intracranial haemorrhage, skull fracture, large established infarcts, hydrocephalus and mass effect. In a head injury or a suspected bleed it is the correct first test — its speed genuinely saves lives. Its limitation is that an acute ischaemic stroke may look entirely normal on CT for several hours, which is why MRI follows in many stroke pathways.
CT Chest / HRCT
Lung tissue is one of the few places where CT decisively beats MRI, because air-filled alveoli produce almost no MRI signal. High-resolution CT of the chest characterises interstitial lung disease, bronchiectasis and emphysema, evaluates nodules and masses, and stages lung cancer. Low-dose CT is also the only screening test shown to reduce lung cancer mortality in long-term smokers.
CT Abdomen and Pelvis
Usually performed with both oral and intravenous contrast. This is the workhorse study for acute abdominal pain — appendicitis, diverticulitis, bowel obstruction, perforation, pancreatitis, abscess — and for staging abdominal malignancy. It is fast enough to be practical in an unwell patient who cannot lie still for an MRI.
CT KUB (stone protocol)
A plain, low-dose CT of the kidneys, ureters and bladder, performed without contrast. It is the definitive test for renal and ureteric calculi, detecting stones that ultrasound and plain X-ray miss, and showing their exact size, position and any resulting obstruction — the three facts a urologist needs. No preparation, no injection, complete in minutes.
CT Angiography
Timed contrast injection with acquisition during peak arterial enhancement produces a detailed map of the vasculature. CT pulmonary angiography is the standard test for pulmonary embolism. CT coronary angiography assesses the coronary arteries non-invasively. Cerebral, renal and peripheral CT angiography evaluate aneurysms, stenoses and vascular malformations.
CT for bones and trauma
Complex fractures — pelvis, acetabulum, calcaneus, wrist, facial bones, spine — are characterised far better on CT than on plain films, with three-dimensional reconstructions that surgeons use directly for planning. CT is also the most sensitive test for detecting subtle fractures that X-ray misses.
Iodinated contrast and its safety
CT contrast is an iodine-based agent injected intravenously. It is a different compound entirely from the gadolinium used in MRI, and the safety considerations differ.
Tell us before contrast
- Kidney disease, dialysis, or a raised creatinine
- Diabetes, particularly if taking metformin
- Previous reaction to contrast media
- Severe asthma or multiple drug allergies
- Thyroid disease, especially hyperthyroidism
- Pregnancy or possible pregnancy
- Myeloma or paraproteinaemia
What you will feel
A brief warm flush spreading through the body, a metallic taste, and a sensation of having passed urine that has not actually happened. All three are expected, harmless and settle within a minute.
What is not expected is itching, a rash, swelling or difficulty breathing. Tell the technologist immediately if any of those occur — the team is trained and equipped for it.
Two practical points. First, metformin: current guidance is that most patients with normal kidney function can continue it, but those with impaired renal function are usually asked to withhold it for 48 hours after contrast. We will advise you specifically. Second, hydration: drinking well before and after a contrast study helps the kidneys clear the agent, and it is the simplest protective measure available.
Radiation dose, explained honestly
CT does use ionising radiation, and pretending otherwise would be dishonest. Here is the useful context.
| Examination | Typical dose | Equivalent background exposure |
|---|---|---|
| Chest X-ray | ~0.02 mSv | About 3 days |
| CT Head | ~2 mSv | About 8 months |
| CT Chest | ~5–7 mSv | About 2 years |
| Low-dose CT chest | ~1–2 mSv | About 6 months |
| CT Abdomen & Pelvis | ~8–10 mSv | About 3 years |
| CT KUB (low dose) | ~2–3 mSv | About 1 year |
| MRI (any region) | 0 mSv | None |
Natural background radiation in India averages roughly 2 to 3 mSv per year from cosmic rays, soil and radon, so a CT head is broadly comparable to what you receive anyway over several months. For a clinically justified scan, the diagnostic benefit overwhelmingly outweighs the theoretical long-term risk — a missed intracranial bleed is a far more immediate danger than a statistical increment in lifetime cancer risk.
The legitimate concern is unnecessary and repeated scanning. That is why we ask for a referral, why we check whether a previous scan already answers the question, and why we apply automatic tube current modulation, iterative reconstruction and paediatric weight-based protocols to keep dose as low as reasonably achievable. If MRI or ultrasound would answer your question without radiation, we will say so.
Preparing for your CT scan
- Plain CT. Head, chest, KUB or bones — no preparation at all. Eat, drink and medicate normally.
- Contrast CT. Fast for four hours, but keep drinking water. Bring a recent creatinine or eGFR if you have kidney disease or diabetes.
- Abdominal CT. You may be given oral contrast to drink over about an hour before the scan so the bowel is opacified.
- Clothing. Loose and metal-free over the area being scanned. You may be given a gown.
- Remove. Jewellery, glasses, dentures, hairpins and anything metallic in the scan field, since metal causes streak artefact.
- Tell us. If you are or might be pregnant, before anything else.
- Bring. Prescription, photo ID, previous scans and films, and your medication list.
What a CT scan feels like
Straightforward, and much less demanding than an MRI. You lie on a flat table which moves through a short, wide, well-lit ring — not a tunnel. Even patients who cannot tolerate MRI generally manage CT without difficulty.
The scanner is quiet apart from a soft whirr. You will be asked to hold your breath for a few seconds during chest and abdominal acquisitions, since breathing blurs the images. If contrast is used, a cannula goes into a vein in your arm and an injector delivers the agent while the scan runs; you will feel the warm flush described above.
Total time in the room is typically five to ten minutes for a plain study and fifteen to twenty-five for a contrast study. After a contrast scan we usually ask you to wait fifteen minutes before leaving, as a precaution.
CT scan cost in Dehradun
| Study | Indicative cost | Time in room |
|---|---|---|
| CT Head — plain | ₹1,800 – ₹3,000 {{VERIFY}} | 5–10 min |
| CT Head — with contrast | ₹3,500 – ₹5,500 {{VERIFY}} | 15–20 min |
| CT Chest / HRCT | ₹3,000 – ₹5,000 {{VERIFY}} | 5–10 min |
| CT Abdomen & Pelvis — contrast | ₹5,000 – ₹8,000 {{VERIFY}} | 20–25 min |
| CT KUB — stone protocol | ₹2,500 – ₹4,000 {{VERIFY}} | 5–10 min |
| CT Pulmonary Angiography | ₹6,000 – ₹9,000 {{VERIFY}} | 15–20 min |
| CT Coronary Angiography | ₹8,000 – ₹12,000 {{VERIFY}} | 25–35 min |
| CT Cerebral Angiography | ₹6,000 – ₹9,000 {{VERIFY}} | 15–20 min |
| CT any single bone / joint | ₹2,500 – ₹4,500 {{VERIFY}} | 5–10 min |
| CT PNS / Temporal bone | ₹2,500 – ₹4,000 {{VERIFY}} | 5–10 min |
Full cross-modality pricing detail is on our MRI scan cost in Dehradun page.
Putting CT dose in terms you can actually use
Original research
Natural background radiation in India averages roughly 2–3 mSv per year from cosmic rays, soil and radon. Against that baseline, a CT head at about 2 mSv is comparable to eight months of simply living here, and a CT abdomen and pelvis at 8–10 mSv to about three years. {{VERIFY}}
The useful conclusion is not that CT is dangerous. It is that a single clinically justified CT is a rounding error against background exposure, while five unnecessary repeat scans are not. That is why we ask whether a prior scan already answers the question before booking another.
Method: typical effective doses compared against Indian average background exposure. Actual dose varies with scanner, protocol and patient size.
Which parts of Dehradun we cover
We serve the whole of Dehradun district, with complimentary pick-up and drop inside city limits. Patients travelling from Rishikesh, Haridwar, Mussoorie and Vikasnagar should mention their location when booking so we can confirm what transport is possible.
- Rajpur Road
- Dalanwala
- Clement Town
- Prem Nagar
- Vasant Vihar
- Jakhan
- Sahastradhara Road
- Race Course
- Patel Nagar
- GMS Road
- Ballupur
- Kaulagarh
- Doiwala
- Selaqui
- ISBT Dehradun
- Mussoorie
- Rishikesh
- Haridwar
- Vikasnagar
Common reference points patients use when giving directions: Clock Tower, Doon Hospital, the ISBT, Graphic Era, Max Super Speciality Hospital and Pacific Mall. If you are coming from Mussoorie, allow extra time on Rajpur Road in the afternoon.
Recommended spoke pages
Build-order recommendation from competitor internal-link anchors. Not yet written.
- CT KUB Stone Protocol in Dehradun —
/ct-kub-dehradun/ - CT Coronary Angiography in Dehradun —
/ct-coronary-angiography-dehradun/ - HRCT Chest in Dehradun —
/hrct-chest-dehradun/ - CT Head in Dehradun —
/ct-head-dehradun/
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Frequently asked questions
How much does a CT scan cost in Dehradun?
A plain CT head typically runs ₹1,800 to ₹3,000. CT chest ₹3,000 to ₹5,000. CT abdomen with contrast ₹5,000 to ₹8,000. CT angiography ₹6,000 to ₹12,000 depending on territory. Contrast studies cost more because of the agent, the cannulation and the extra acquisition phases.
How long does a CT scan take?
The scan itself takes seconds. A plain CT head is usually complete within five to ten minutes of lying down. Contrast studies run fifteen to twenty-five minutes because of cannulation and multi-phase imaging, plus a fifteen-minute observation period afterwards.
Is CT radiation dangerous?
CT uses ionising radiation and the dose is higher than a plain X-ray — a CT head is roughly comparable to eight months of natural background exposure. For a clinically justified scan the diagnostic benefit far outweighs the small theoretical risk.
The real issue is unnecessary repeat scanning. We use dose-modulation and iterative reconstruction, and if MRI or ultrasound would answer the same question without radiation, we will tell you.
Should I have a CT or an MRI?
Your referring doctor decides, but broadly: CT for bone, acute bleeding, stones, lungs and emergencies; MRI for brain detail, spinal cord, discs, ligaments and cartilage. If a device or claustrophobia rules out MRI, CT is often a workable alternative — ask us.
Do I need to fast?
Only for contrast studies — four hours, with water allowed. Plain CT of the head, chest, bones or KUB needs no fasting. We confirm which applies when you book.
Can I have a CT scan if I am pregnant?
Tell us before anything else. CT is generally avoided in pregnancy, particularly for the abdomen and pelvis. Where imaging is unavoidable, ultrasound or MRI is preferred. If CT is genuinely necessary the dose is minimised and shielding applied, and the decision is made jointly with your obstetrician.
Can I have a CT scan with metal implants?
Yes. There is no magnetic field, so implants pose no safety risk. The only issue is streak artefact radiating from dense metal, which can obscure adjacent structures. Metal artefact reduction reconstruction reduces this considerably. This is one situation where CT is easier than MRI.
Will I be enclosed in a tunnel?
No. A CT gantry is a short, wide, open ring rather than a long tunnel, and you pass through it in seconds. Claustrophobia is rarely a problem with CT even for patients who cannot tolerate MRI.
