# CT scan v. MRI **URL:** \ **Category:** Factual Questions\ **Created:** [October 28, 2003, 3:29pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033 "2003-10-28T15:29:11Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![DaddyTimesTwo](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@DaddyTimesTwo](https://boards.straightdope.com/u/DaddyTimesTwo)\ **Post date:** [October 28, 2003, 3:29pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/1 "2003-10-28T15:29:11Z")
My son has a health condition that requires regular head CT scans, every six months or every year, depending on circumstances. These allow his neurosurgeon to make decisions as to his treatment etc. I understand that there is a different technology at work between the two (xray vs magnetic fields), but what makes CT scans better for my son? The result in either case would be a picture of his head, right? What criteria are used to decide between the two? I’d ask the surgeon about it but I never think of it when we’re there. ---
**Author:** ![Saranga](https://avatars.discourse-cdn.com/v4/letter/s/d6d6ee/32.png) [@Saranga](https://boards.straightdope.com/u/Saranga)\ **Post date:** [October 28, 2003, 6:14pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/2 "2003-10-28T18:14:12Z")
MRIs are more precise than CT scans and this makes them prone to false positives. I believe this has more to do with our incomplete understanding of the human body than any flaws in the technology. For example, an MRI may show a clump of tissue that appears to be a tumor. After a biopsy (and much discomfort to the patient), it is revealed to be merely a clump of tissue. Similarly, many patients on an MRI will appear to have a herniated disc, even though they have no pain or other problems. For this reason MRIs are restricted in use even though the high false positive rate is usually outweighed by the potential benefits. ---
**Author:** ![hlanelee](https://avatars.discourse-cdn.com/v4/letter/h/3bc359/32.png) [@hlanelee](https://boards.straightdope.com/u/hlanelee)\ **Post date:** [October 28, 2003, 6:21pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/3 "2003-10-28T18:21:02Z")
This has nothing to do with your son’s condition, it’s just my opinion but CT scans are reletively comfortable and getting an MRI is like being in HELL. I will never get another one if I’m concious. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 28, 2003, 6:32pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/4 "2003-10-28T18:32:54Z")
From: [http://www.cmicenters.com/info-healthpro/mrivsct.html](http://www.cmicenters.com/info-healthpro/mrivsct.html) > [@](#): > > Questions frequently arise regarding the utilization of CT versus MRI scans to obtain the best diagnostic outcome for the patient. In general, MRI is the procedure of choice for all neurologic and orthopedic diagnoses, while CT is the preferred modality for examining the chest, abdomen, pelvis, and skull base. Note that CT and MRI can also be used in cross-over problem solving from the alternative modality. There’s a lot more data at the site of the cite. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 28, 2003, 6:36pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/5 "2003-10-28T18:36:10Z")
> [@](#): > > \*Originally posted by Saranga \* > \*\* For this reason MRIs are restricted in use even though the high false positive rate is usually outweighed by the potential benefits. \*\* Um, no, not really. Not in my clinical experience. They’re each good in certain areas, and the combination use can be helpful too, as noted in my cite. Do you have a cite for your assertions? CT scans show a lot of disc protrusions which are asymptomatic also. That’s hardly a flaw of the test; it tends to reflect reality. Many people have asymptomatic disc protrusions. QtM, MD ---
**Author:** ![DaddyTimesTwo](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@DaddyTimesTwo](https://boards.straightdope.com/u/DaddyTimesTwo)\ **Post date:** [October 28, 2003, 9:16pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/6 "2003-10-28T21:16:34Z")
Hmmm. Thanks for the link, **QtM** , although it still doesn’t quite explain the CT scan preference. My son has a neurological disorder, okay, I’ll go ahead and say it, called hydrocephalus. the CT scans are done to examine the ventricles and make sure the shunts are working and placed correctly. The link indicates that MRI is the preferred “modality” for neurological work, which contradicts the treatment my son is receiving. I’ll have to be sure and ask the doc next time we’re in. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [October 28, 2003, 10:40pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/7 "2003-10-28T22:40:35Z")
Well **DaddyTimesTwo** , I don’t know if your doc will fess up to this or not, but the biggest reason CT is done over MRI in this case would most likely be money. MRIs are much more expensive than CTs. How old is your son? MRI requires longer scan times and therefore requires sedation in some children, which is also a deciding factor, but honestly, money is the biggest issue. Insurance companies may be the ones who decide CT is “good enough”. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [October 28, 2003, 11:24pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/8 "2003-10-28T23:24:32Z")
Add to that the possibility that all they need is a quick glance to see if the ventricles are enlarging or not. Quicker, less traumatic (not so much downtime in scary tube) and if there seem to be changes, then go on and have the MRI. That’s my wild ass semi-educated guess anyway. Ask your neurosurgeon. ---
**Author:** ![Major\_Feelgud](https://avatars.discourse-cdn.com/v4/letter/m/3be4f8/32.png) [@Major\_Feelgud](https://boards.straightdope.com/u/Major_Feelgud)\ **Post date:** [October 29, 2003, 12:29am UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/9 "2003-10-29T00:29:38Z")
Quick answer: CTs are for looking a bony structures. MRIs are for looking at soft tissues. A CT is merely a series of x-rays which software then uses to produce a series of 2-D films. A MRI excites hydrogen atoms which then vibrate and gives off signals which are detected. The more hydrogen a tissue has, the bigger the signal. Since some tissues have more water in them, so you can differentiate it from other types of soft tissues. Soft tissue is anything which isn’t bone. Some insiders have told me that no one really knows what the long term effects of MRI is since it hasn’t been that long since MRIs were commonly used. The strength of the magnetic field is extremely strong, stronger than can be found in nature. I’m wary of MRIs myself, at least the side effects of CTs (x-rays) are known. There has been a recent study done showing that the effects of many x-rays were not as bad as they thought. I don’t know why the neurodoc would be using CTs unless it was for cost or expediency. About 7 years ago, the joke amongst doctors was that the only reason why you gave a patient a CT was because an MRI was unavailable. ---
**Author:** ![DaddyTimesTwo](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@DaddyTimesTwo](https://boards.straightdope.com/u/DaddyTimesTwo)\ **Post date:** [October 29, 2003, 11:26pm UTC](https://boards.straightdope.com/t/ct-scan-v-mri/210033/10 "2003-10-29T23:26:00Z")
He has just this year been able to get the CT without sedation which is GOOD NEWS. The sedation was incredible as he would be increasingly irate until he fell asleep. I would guess that **QtM** is right on the money, and that $$$ plays a role as well. They just need a quick loook, CT is a piece of cake and much less expensive. Thanks.