Topic: Ultra sound ,CT Scan,MRI and PET/CT-a reprint message
Hi, The following is a reprinted message about CT and MRI scan,it may be easier and of value to those new members who try to search for this info if I duplicated it here again.
Ultrasound (US)of the liver or abdominal area provide the most inexpensive way to check on the hepatobiliary system.It is of great value too when it is used intraoperatively to detect tumors that the liver surgeon cannot see with his/her naked eyes during surgery.But its result is depended on the person who performs the US as well as the interpretation of the image; when the US result is inconclusive,CT scan or MRI is recommended.
Cat Scan is for diagnosis purpose.(including initial diagnosis and follow up after resection or chemo treatment for CC. Both MRI and Cat Scan are used to look for structural changes.PET scan is used to look for functional changes(activity) of the tumor.
According to one study compared 20 intrahepatic patients images ,the extent of the tumor enhancement was similar with both MRI and CT methods,however the relationship of the tumor to the vessels and surrounding organs was more easily evaluated on CT scan as opposed to MRI.But for perihilar tumors CT also has limited sensitivity for extra regional nodal disease(ie metastases to the periaortic,pericaval or celiac artery lymph nodes.)---from uptodate .com.
(My own experience told me that MRI with contrast is a good "follow-up" alternative to use right after initial CT with contrast shown inconclusive report in the early stages of CC development .Using MRI or PET to rule out recurrence or give the patient an early and more options to treat the recurrence while the CC is smaller than 2-3cm.MRI can also find additional small lesions which CAT SCAN missed.
I will recommend PET scan right after CAT or MRI if recurrence is confirmed or small lesions detected by MRI but not sure whether they are cancerous or not.This will give the doctor more info about the lesion such as whether the lesion has metastasized or give the doctor a more informed idea what he/she saw on the M R I or CAT scan indeed is a tumor that has metabolic activity(maxSUV) value and required immediate attention such as chemo therapy or resection,RFA,chemoembolization, radioembrolization, PDT,SBRT .
By doing so,the doctors will not be confused with and discard the lesion as being part of the artery or hepatic vein or other forms of lesions and ask the patient to return in 3 months to repeat the scans to make sure.As you all know, 3months is a lot of valuable time for patients as well as caregivers. Who wants to wait for another three months? I think this is the part of early detection that we,ourselves, can monitor and provide the early benefit of more treatment options to the patient.
PET can find or confirm cancer metastasized activities in the other parts of the body.PET may not be a good choice to locate NEARBY metastasized cancer activity such as the lymph nodes that are very close to the primary site of CC because the closest distances between the lymph nodes and the CC.)
However the result of PET may be also related to inflammation status of the organ systems rather than indications tumor activities .(such as infections that is not related to the cancer)
PET Scan allows visualization of CC because of the high glucose uptake(SUV) of the bile duct epithelium(the lining )-- the "Hot spots" will light up on the PET scan and show the relative cancer activity of the lesion by the SUVmax value.
A PET scan therefore can help to tell if the bile duct obstruction is caused by a cancer or benign lesions.PET scan can be useful in determining the cancer may have spread or return after treatment.
In general SUVmax value>3.9 is an indication of cancer activity of the lesion while value<3.9 may not.In general, the more aggressive cancer,the higher the FDG uptake it will be.But the diagnosis must also be made in conjunction with the size or the volume of the lesion that shows the SUV max activity. (the SUVmax range that I saw so far is between 2.0-36.4 in CC);and PET is more accurate when using in intrahepatic lesions than extrahepatic lesions in cholangiocarcinoma diagnosis.
Check the link below for additional information about PET (#5 item of the message)
Some hospitals equipped with machine that is able to perform both A PET and CT scan at the same time(PET/CT scan) ;this allows the radiologist to compare areas of higher radioactivity on the PET with the appearance of the affected area on the Cat scan. But according to the radiologist I talk to , A (PET/CT scan ) is not the SAME as if you take them SEPARATELY;(PET/CT scan is PET plus CT scan WITHOUT contrast).
Remember Ct scan is for structural and PET is for functional (activity) visualization of the lesion. That is why sometimes doctors order a PET scan on this 3 month checkup and on the next checkup, he/she orders a CAT Scan with contrast or MRI instead.
The current recommendation from NCCN in the States for extrahepatic and intrahepatic cholangiocarcinoma are the same for re-sected patients(R0 )with clear margin-for surveillance purposes--consider imaging every 6 months for 2 years.(But based on my personal experience EVERY 3-4MONTH is more realistic and it can provide more early options for treating the recurrence since the sizes and extended involvement of the tumor is still relatively small.It is because in general,the tumor lesion will be double in size every 3 months ,some are slower,some are faster in grow. depend on the type of cancer cells.)
Additional info. from uptodate.com
MRI and CAT SCAN (CT) have similar resolution for liver lesions.
CT has been considered to be superior to MRI for evaluating extrahepatic organs and calcifications. MRI is more specific than CT for differentiating cavernous hemangiomas,diffuse hepatic steatosis and focal fatty infiltration.
Also MRI should be reserved for the evaluation of lesions less than 2 cm,or lesions located adjacent to the heart or to major intrahepatic vessels.
If you are allergic to the IV iodinated contrast agent used for CT,then MRI is the alternative because the contrast agent used is different than CT. and MRI is not involved radiation .
I hope the above info. helps.