Headache: Do You Need a CT or MRI Scan?

At a Glance

Emergency first: when not to book a scan appointment

Go straight to a hospital emergency department, not an outpatient scan centre, if a headache comes with any of these (call 108 for an ambulance if needed):

• A sudden, severe headache that peaks within about a minute: the worst headache of your life
• Weakness or numbness of the face, arm or leg, slurred speech, confusion, drowsiness, or sudden loss of vision, double vision or a drooping eyelid
• A first fit (seizure)
• A head injury followed by a blackout, vomiting, drowsiness or confusion, or any head injury while taking blood thinners
• Fever with a stiff neck, or a rash that does not fade when pressed
• A severe new headache in pregnancy or in the weeks after delivery
• A painful red eye with blurred vision or haloes around lights

These can mean bleeding, a stroke, a clot or an infection, and a hospital can scan and treat in one place.

Most headaches do not need a scan

Tension-type headache (a band-like pressure on both sides) and migraine (throbbing, often one-sided, with nausea or sensitivity to light, sometimes preceded by flashing lights or zigzag lines called an aura) are diagnosed from the story of your headaches and a normal examination. In these headaches a scan almost never shows a cause, so headache and radiology guidelines advise against routine scans.

Painkillers taken on roughly 10 to 15 or more days a month for three months or more can themselves keep headaches going (medication-overuse headache). A scan does not show this, but your doctor can help.

In Hindi, headache is सिरदर्द (sirdard); in Marathi, डोकेदुखी (dokedukhi).

When doctors ask for a brain scan for headache

Your family doctor, physician or neurologist may ask for imaging when there are warning features, such as:

• A new headache after about 50 years of age, or a clear change from your usual pattern
• Headache that keeps getting worse over weeks, or wakes you from sleep with vomiting
• Headache brought on by coughing, straining or exercise, or clearly worse on standing or on lying down
• Headache with a seizure, unsteadiness, a change in personality, or problems with vision or speech
• Swelling of the optic nerve at the back of the eye (papilloedema) found by an eye doctor: this usually needs a scan the same day
• Headache in someone with cancer, HIV or other low immunity
• An unusual migraine aura (starting for the first time after 50, or lasting more than an hour), or one-sided attacks around the eye with a red, watering eye (cluster-type headache)

If any of these comes on suddenly, or new weakness, numbness or speech trouble appears, use the emergency list above.

CT or MRI for headache: which test for which question?

For a headache that has built up over weeks, MRI is usually preferred: it shows the brain in more detail and uses no radiation. CT is chosen when fresh bleeding or a head injury is the question, usually in an emergency department, or when MRI is not possible:

• MRI brain: tumours, including small ones and those at the back of the brain, the pituitary gland, inflammation, infection, multiple sclerosis, signs of raised or low pressure, and Chiari malformation (the lowest part of the back of the brain sitting lower than usual, into the top of the spinal canal). No radiation. See brain MRI.
• CT brain: seconds to scan; shows fresh bleeding, fractures, swelling, enlarged fluid spaces (hydrocephalus) and calcium, but can miss small changes. Uses X-rays. Suits people who cannot have MRI. See CT brain.
• Sinuses: headache over the cheeks and forehead is often migraine. If an ENT doctor suspects chronic sinusitis, usually when symptoms continue despite treatment, a CT PNS (HRCT PNS, sinus CT) shows the sinuses in detail.

Prescriptions may say NCCT brain (plain CT), CECT brain (CT with contrast) or 'MRI brain with angio' (MRI with MR angiography).

When the blood vessels are the question: MRA and MRV

MR angiography (MRA) shows the brain's arteries, usually without an injection; MR venography (MRV) shows its veins, with or without a contrast injection. Both are usually added to a brain MRI in the same visit. Doctors ask for them:

• MRA: to look for an aneurysm (a bulge in an artery wall) when two or more parents, brothers, sisters or children have had one, in some people with polycystic kidney disease, or to follow up a known aneurysm
• MRV: for a suspected clot in the brain's veins, such as a headache that worsens over days, sometimes with blurred vision, particularly after childbirth, on the contraceptive pill or other hormone tablets, or with a clotting disorder; and when pressure in the head is raised

Most aneurysms that have not bled cause no headache, so MRA is not a routine test for migraine. A suspected clot in the veins is often urgent: follow your doctor's advice on where and how soon to be scanned. See MR angiography and venography.

How to prepare

Our team confirms the exact preparation when you book on WhatsApp. In general:

• Plain MRI, MRA, MRV without contrast, or plain CT: no fasting; take your usual medicines.
• If contrast is planned: about 4 hours without food; water is allowed. A recent kidney function (creatinine) report may be requested; if you do not have one, the test can be done at the centre before your scan.
• Mention allergies, any earlier reaction to contrast, kidney disease and diabetes medicines such as metformin: for CT contrast we check your kidney function (eGFR) and advise you. Do not stop any medicine on your own.
• If you are or could be pregnant, tell us before booking, especially before any CT or X-ray.
• When you book an MRI, tell us about any pacemaker, implant, aneurysm clip, cochlear implant, brain shunt (some shunt valves need checking after MRI) or metal in the eye, and bring the device card. Some pacemakers and MR-conditional implants can be scanned here under supervision, following the device's conditions; others cannot. See our MRI preparation guide.
• If sedation is planned, our team gives you separate fasting instructions; an adult must accompany you home, and you should not drive for the rest of that day.
• Bring your prescription and earlier brain scans and reports.

What happens, and is it safe?

In the MRI you lie still with a light coil around your head. The Fujifilm ECHELON Smart 1.5T uses quieter scanning with in-scanner music. A brain MRI usually takes about 20-45 minutes, longer when MRA, MRV or contrast is added. If closed spaces worry you, tell us when booking: sedation is available when needed, under the supervision of an anaesthesiologist. For a CT, you lie on a table that moves your head into a short, wide ring, and a plain scan usually takes about 10-15 minutes in the room.

MRI uses no radiation. A plain head CT gives a dose roughly similar to several months to a year of natural background radiation (see CT scan radiation explained); children are more sensitive to radiation, so outside emergencies MRI is usually preferred for them. Contrast is added only for specific questions, such as a suspected tumour, infection or low-pressure headache; you are told first, and serious reactions are rare.

If you are pregnant, tell us first: MRI without contrast can be done when needed, MRI contrast is usually avoided in pregnancy unless essential, and a head CT gives the baby very little radiation, but your doctor and our radiologist decide together. In an emergency, pregnancy should not delay a head CT that a hospital doctor advises.

Your brain scan at AV Scan, Dadar West

Unsure whether your prescription asks for MRI, CT, MRA or MRV? Send us a photo on WhatsApp; our team checks it with you and confirms the preparation and the exact price before your visit.

• Reported by our radiologists, Dr. Avinash Bansal and Dr. Vaishnavi Bansal (both MD Radiology), who compare it with any earlier scans you bring
• Fujifilm ECHELON Smart 1.5T MRI; Fujifilm Supria CT
• Most reports the same day, sent to your WhatsApp; if something needs urgent attention, we contact your referring doctor directly
• Cashless with most major insurers and TPAs; empanelled for CGHS, ECHS and MJPJAY (see insurance and TPA)
• Open Monday to Saturday 8am-10pm and Sunday 8am-5pm; ground floor with step-free entry, near Shivaji Park and Siddhivinayak Temple