Computed Tomography (CT) is an imaging procedure commonly used to determine locations and sizes of tumors, so-called staging of disease. CT is often used to measure response to treatment, especially in clinical trials.
X-ray images are taken from different angles and then processed by a computer to create detailed pictures of the inside of the body. Each section of the test involves lying still for about 10-30 minutes. The images produced are in cross sections.
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ACR accreditation means: "Your hospital, clinic or health center has voluntarily gone through a rigorous review process to be sure it meets nationally accepted standards. The personnel are well qualified, through education and certification, to perform and interpret your medical images and administer your radiation therapy treatments. The equipment is appropriate for the test or treatment you will receive, and the facility meets or exceeds quality assurance and safety guidelines."
What to expect and how to prepare
Bring water with you so that you can drink after the test to more quickly eliminate the contrast material.
Depending on the area to be scanned, you may be asked not to eat for approximately 4-6 hours prior to the test.
When you arrive you may be asked to drink a solution that has contrast agent. This is used to enhance the image visibility of certain tissues or blood vessels. Before drinking the contrast, however, the nurse or technician will ask about your medical history to identify conditions, such as allergies, that may put you at higher risk of reaction to the contrast material, or indicate problems you may have eliminating the material after the exam.
About contrast agents
CT contrast are agents (liquids) and are sometimes referred to as "dye". CT contrast is used to make specific organs, blood vessels and/or tissue types "stand out" with more image contrast to better show the presence of disease or injury. Thus CT contrast highlights specific areas of the resultant CT image or "dyes" it." imaginis.com
Note: It is important that patients consult the imaging location performing their CT exam for specific instructions to follow when contrast will be used.
Minimizing Adverse Reactions to Contrast Agents
Adapted from, and with links to massgeneralimaging.org
Is Contrast Imaging Necessary?
Identifying the At-Risk Patient
Minimizing Contrast Agent Reactions and Nephrotoxicity
Scheduling and Reporting
Further Information
References
"Although significant adverse reactions to iodinated contrast agents are rare, they do, justifiably, arouse concern among patients, referring physicians, and radiologists.
Most reactions are mild and self-limiting, such as flushing, nausea, vomiting, pain at the injections site, pruritus [itching], headache, and mild urticaria [hives]. They are, nevertheless, unpleasant for the patient.
The very rare severe reactions, estimated to occur in 0.004 – 0.04% of patients, include life-threatening anaphylactoid reactions, cardiac dysrythmias and arrest, and cardiovascular and pulmonary collapse. These reactions are idiosyncratic and difficult to predict since they may happen once but never again."
Depending on the scan, IV contrast may be used.
The technologist begins by positioning the patient on the CT table. You may be given pillows to help hold still and in the proper position during the scan. The table will move slowly into the CT scanner.
Drink water after the test: "Hydration lowers the risk of renal failure and is especially important in patients who have mild renal insufficiency, diabetes, or multiple myeloma. Patients should be encouraged to drink plenty of clear fluids both before and after the procedure." massgeneralimaging.org
Ask for copies of the images
Patient-to-patient advice: "When you have these scans, remember to ask the technician for copies of the films (for your records). They don't mind printing an extra CD or print - as long as you tell them upfront BEFORE they sent the "number of copies". Everything is digitalized and it makes it so much easier to keep your records. In the olden days, we would have the big, heavy CT films or MRI films we carried around. So, the improvements are welcomed, however, I have also learned that computers crash and some digital films get lost, hence, my recommendation that you ask for copies. If you are nervous about asking for this, call them before you go and find out if you can bring a CD for them to back up to. In this way, you will learn if your facility is co-operative or not. And naturally, always ask for a copy of the radiology report to be mailed to your home for your records.
Having CTs spaced on different days is very, very common. Personally, I had to have them several days apart because I am very sensitive to the contrast dye. I also have to be pre-medicated with Benadryl and Prednisone. It is one of the reasons that I "gave up" CTs for monitoring remission. You don't have this type of control while in a clinical trial and you must comply with the demands of the trial protocol. Those of us who have already participated in a trial understand how confusing it can be when they request something of you and you don't understand the why of it.
One way that you might look at the four areas of scan is "insurance" - while it is not necessary to have, it is good backup against unseen or undiagnosed areas of disease involvement. Also, a head/neck scan now, if clear, will be your baseline for the future. Hopefully, you will never have evidence of disease from the neck up, but if you should have questions, you could refer back to those scans.
One of my patients has a little "thumb" drive (USB 2.0 flash driver) or other named device she carries with her for her scans. The local imaging center copies her scans onto her zip/flash driver and she has it to go back to her home computer. I was with her when she had her physician's appointment (who didn't have the "films" yet) so Linda just popped her little flash drive into his laptop and up came her scans. It worked out so well, but I think it depends on your facility and their "spirit of cooperation". Some imaging centers act like they are guarding the secrets of the universe and YOU are not allowed to know the secrets of the universe because you don't wear a white jacket!!! "You must ask your doctor!!" ~ Jama Beasley (advisor to PAL, and patient navigator)
Factors that can influence interpretation of results
Size of lymph nodes can be influenced by inflammatory reactive conditions.
"diffuse lymph node enlargement secondary to infectious or granulomatous diseases cannot be discriminated from metastases or systemic lymphoma." Oncologic Imaging: A Dilemma Still Waiting to Be Solved
Scar tissue - CT cannot distinguish between scar tissue and viable tumors.
Following treatment "a residual mass persisting on CT after treatment poses a common clinical dilemma: it may indicate the presence of viable lymphoma, which requires further treatment, or it can be benign, consisting of only fibrotic and necrotic tissues." PMID: 12644887 For this reason PET or Gallium scans may be used after treatment to help differentiate active disease from scar tissue.
Small changes in the size of nodes could be accounted for by the angle of the equipment in relation to the patient.
"In a multiplanar reconstruction CT program (CT/MPR), the altered gantry angle corresponding to the patient's position during scanning for multiplanar reformatted CT may cause distortion of the image. The aim of this study was to quantitatively assess the distortion in reformatted central panoramic and cross-sectional images owing to the change of gantry angle. " birjournals.org
Recommended Resources
About CT Cancer Help. Org | radiologyinfo.org
Minimizing Adverse Reactions to Contrast Agents massgeneralimaging.org
Q & A iowaimaging.com
What is a CT Scan? | What will the exam be like? | What is a contrast media?
How long will the exam take? | When will I know the results?
PET/CT
"The highly sensitive PET scan detects the metabolic signal of actively growing cancer cells in the body and the CT scan provides a detailed picture of the internal anatomy that reveals the location, size and shape of abnormal cancerous growths.
Alone, each imaging test has particular benefits and limitations but when the results of PET and CT scans are "fused" together, the combined image provides complete information on cancer location and metabolism.
The bottom line is that you can have both scans - PET and CT - done at the same time." petscaninfo.com
PET/CT Imaging radiologyinfo.org
PET/CT: Patient Preparation massgeneralimaging.org
Also See
Comparing CT and MR Images Lymphomation.org
Side-by-side comparison of MR and CT images
Comparing CT with MRI Lymphomation.org
Abstracts and resources on the subject.
About Long Term Risks of CT Imaging
CT risks: Debate continues about risks, and for which populations? cancernetwork.com
The authors recommend better equipment and techniques to lower radiation exposure and the alternative use of MRI and ultrasound, ***especially for infants and children.*** They urge physicians to avoid inappropriate CT utilization. ...
Arl Van Moore, Jr., MD, chair of the ACR board of chancellors, worried that patients may mistakenly avoid what the ACR characterized as "life-saving medical imaging care," because of the article. "They may be terribly confused and unduly distressed by some of the statements in this study," he said.
"Radiation effects are lat