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Pet, CT, MRI ???

Posts: 1598
Joined: Aug 2012

Wondering how these are typically used.   If I'm remembering correctly, my husband's last pet scan was in March - before surgery and only showed the rectal tumor.   Tumor was removed in April.  His CEA has been good since surgery.  Though it's been going up slightly, it's been under 1.0 since surgery (.5 in June, .6 in July and .7 in August)  Had a CT scan on Saturday and we find out the results this afternoon.   I read somewhere - think it was on colonclub, that CT is not the best for picking up lymph nodes.   He's stage 4 because of distant nodes (para-aortic) at diagnosis - those were removed in Sept and nothing else has lit up since, but he's been off chemo since March.

So, when is MRI typically used?  Tans - does your wife have yearly MRIs?   I know she had para-aortic nodes also - is MRI better at picking up nodes?  

 Onc said she didn't think she could get another Pet Scan approved at this point, unless something showed up on the CT.  Just wondering if monthly CEA checks and 6 month CTs are the standard?


LivinginNH's picture
Posts: 1456
Joined: Apr 2010


Hi Jen,

I don't know if this is standard or not, but Rick had a PET/CT with contrast every three months.  He never had an MRI for a cancer diagnosis of any kind.  Not sure, but maybe they only do a PET if the CT shows active tumors (???).  Sorry, can't help more than that.

Best wishes,


Posts: 2215
Joined: Oct 2011

I have had mostly Ct scans and CT/PET scans over the past 7 1/2 years. However I did do an MRI twice. Each time was after a CT scan where a suspicious spot appeared but was too small to confirm if it was cancer. The first time was 5 years ago and the MRI confirmed the spot wasn't cancer I think because it didn't show up. I just had my second MRI last month for the same reason. This time the spot was still visible but not as clear as the CT image. Therefore it was inconclusive.

tanstaafl's picture
Posts: 1144
Joined: Oct 2010


We used the MRI this time, the only time so far, especially for a diffusion weighted inspection of the peritoneum and an enhanced, high resolution liver scan.  Also the change of technology sometimes helps see something that the CT misses.  The MRI does not do as well on the air filled lungs as CT. The radiologist liked our quality (3+ hours), procedures can vary between MRI centers.  I believe that some centers have introduced an improved CT with PET/CT now, more comparable to enhanced solo CT.

She's stayed on mild UFT-LV chemo (non-US), cimetidine, PSK etc, etc everyday because we're worried about microscopic mets and stem cells, old and new, long term.  The surgeons said chemo forever.  

We are usually running 8-12 months between scans with low surgical residue, good immunochemo activity, and relatively good CEA, CA19-9 and liver function markers like LDH and GGTP (also occasional CA72-4, AFP markers 12-18 mo, d-dimer or fibrinogen).  She has heavy duty blood test coverage, usually done every 3-5 weeks depending on prior results. Even 2 weeks if I am concerned any about rise and testing more chemistry.  We "invest" in her bloodwork and supplements. 

Finding a balance between scans, tumor (in)activity and blood tests gets very personal. My wife avoids scans and handles the blood testing fairly well.  The family might be a little more comfortable if she scanned more regularly at 6-7 months, I'm thinking of midterm Xrays - quick, low dose, cheap and potentially effective.


annalexandria's picture
Posts: 2574
Joined: Oct 2011

but the CT scan alone didn't work at all for me.  It was never able to pick up the tumors until I had reached "doubled over in pain, head to ER, land in emergency surgery" status.  After finding this out the hard way, I switched (after some arguing with doc) to PET/CTs every three months (now out to 6 months).  And the first scan I did proved that this was the best course for me...CT failed to pick up a 2 cm tumor in the small intestines that the PET was able to "see".  I think it was a lot better for me to take it out before it got much bigger, so I'm glad I'm doing it this way.  It did, however, require the threat of a lawsuit.  Fun!

Keep us posted, Jen-thinking about you guys today.


traci43's picture
Posts: 689
Joined: Jul 2007

In my experience, a CT scan shows potential tumors and is used when CEA is low.  If CEA is over 5, then there is a chance of a PET scan picking up some activity.  PET scans generally show metabolic activity but aren't as good at defining tumors.  I'm not sure what an MRI would show, I've only had one and the doctor ordered the wrong one (bones instead of organs).  That's my experience, my HMO has the CT machines and contracts with a mobile PET Scan trailer that comes by weekly, which may affect how good the scans are.  My HMO has the same schedule monthly CEA tests with 6 month CT scans.  After a year they will go to every 2-3 months for CEA, still 6 month CT scans.  Good luck!

Anonymous user (not verified)

CT scans combine a rapid series of x-rays into slices of the body to differenciate anomolies from normal tissue, but they are not diagnostic unless the radiologist is looking for something known from a previous history or occurance. Unless one of the newer 3D scanners is used the margins of detail may not be as definitive.

MRI is a very strong magnetic field that aligns certain atoms within tissues so that a very definitive line and placement of margins of tissues is seen. But again the diagnostic capability is dependant on interpretation according to history and other laboratory results.

The PET scan is taken soon after injecting a radiotraceable glucose into the blood circulation.  Since cancer cells have a high metabolic rate, they absorb the glucose at a rapid rate and the radiographic glucose lights up in shades of red to bright yellow in the active cells. Most PET scans combine a 3D CT that shows the location and distribution and size of the active cells. A radiologist can interpret the size, activity, and definite location of even the small lymph nodes that are cancerous. Since certain parts of the body, such as the brain and lungs, also have a high metabolic rate the results may not be definitive unless other diagnostic lab, biopsies, and history are put together.

In short I prefer the PET/CT for a definitive look at the amount of activity in the cancerous cells. A PET/CT may show three active tumors and a few calcified (dead) ones. But an MRI will show all the tumors without knowing which ones are active.

My insurance pays for a PET/CT every 3 months, and a CEA once a month. I'll take the PET/CT over the CT or MRI any day. Still the docs are smarter than I am.    Dan

Posts: 1598
Joined: Aug 2012

Thank you all for weighing in.  I try to trust the doctor, but feel myself questioning everything.  She is very patient and tolerant with me. 

Posts: 1170
Joined: Sep 2012

Keep it up.  Question everything.  Hubby is super lucky to have you in his corner.

Posts: 2215
Joined: Oct 2011

I requested an mri for my next scan and will continue to do so since there is no radiation involved.

tanstaafl's picture
Posts: 1144
Joined: Oct 2010

The MRI is a lot slower for us (did a thorough job!), and doesn't give as good of coverage in the lungs. So coverage balance might become a factor.  To reduce the Xray dosage, we use newer CT machines  - which is partly hardware like 128 and 256 slice scanners and new 64s, and partly newer algorithms that simply crunch the existing detector data more completely.   Some pts have done scans of the lower abdomen and simple Xray (~1/50 dose) of the chest. 

MaryCarol5's picture
Posts: 96
Joined: May 2013

I wish I could help here.   My personal experience is limited to PET since I have a severe allergy to contrast.  I can tell you through my professional experience that PET seems to be the best at detecting most tumors regardless of size but of course, there are exceptions.  The problem is insurance covering these very expensive scans and most people opt for the adequate and less expensive ct/mri. 

All my best


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Joined: Oct 2009
Posts: 1598
Joined: Aug 2012

Interesting...thanks for posting the link.

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