Scans and tests explained
CT, MRI, PET-CT, ultrasound and the blood tests used in follow-up — what each one shows, what it cannot show, and how to read the words in the report.
6 min read · Part of Follow-Up & Surveillance
Written by The LifeAfterward editorial team from the sources listed at the end of this page.
Not individually reviewed by a clinician. This page is written from published clinical guidance, listed in full at the end, and is general information rather than medical advice — your own team knows your case. See our editorial standards.
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In short
- Different scans answer different questions; more detail is not always better, and no scan proves the absence of cancer.
- Radiology reports are written for clinicians. Words like "unremarkable", "indeterminate" and "stable" have specific meanings that are less alarming than they sound.
- Tumour markers are useful for some cancers and unreliable for others — they are interpreted as a trend, not a single number.
- Incidental findings are common and usually harmless. A finding is not a diagnosis.
What this means
Understanding what a test can and cannot show removes a great deal of unnecessary fear. A CT scan reporting "no evidence of recurrent disease" is genuinely good news; it does not mean every cell has been counted. Equally, an "indeterminate" nodule is usually just something the radiologist cannot classify from one image, which is why the answer is often another scan in three months rather than a biopsy.
The scans
- CT (computed tomography)
- X-rays taken from many angles and reassembled into cross-sections. Fast, widely available, good for chest, abdomen and pelvis. Uses ionising radiation, and often uses an iodine contrast injection.
- MRI (magnetic resonance imaging)
- Uses a strong magnetic field rather than radiation. Better than CT for brain, spinal cord, liver, pelvis and soft tissue. Slower, noisier, and not possible for some people with metal implants.
- PET-CT
- A radioactive sugar tracer shows where cells are unusually active, combined with a CT for anatomy. Very useful for some cancers, but inflammation and infection also light up, so a "hot spot" is not automatically cancer.
- Ultrasound
- Sound waves, no radiation. Good for thyroid, testes, liver, breast tissue and lymph nodes near the surface, and for guiding biopsies.
- X-ray
- A single projection image. Quick and useful for bones and lungs, but far less sensitive than CT.
- Contrast
- A dye given by injection or drink that makes blood vessels and some tissues stand out. Tell the team about kidney problems, diabetes medication, or previous reactions.
What the words in the report mean
- No evidence of disease (NED)
- Nothing on this scan looks like cancer. It is the phrase people wait for. It describes what the scan can see, at this resolution, today.
- Unremarkable
- Normal. Radiologists use it to mean "nothing worth remarking on".
- Stable
- Unchanged compared with the previous scan. In follow-up this is good news.
- Indeterminate
- The radiologist can see something but cannot say what it is from this image. Usually followed by a repeat scan after an interval, which is a normal and reassuring plan rather than a delay.
- Incidental finding
- Something unrelated to the reason for the scan — a cyst, a gallstone, a small nodule. Very common, usually harmless.
- Lesion
- A neutral word for an area that looks different from the tissue around it. It does not mean cancer.
- Sub-centimetre nodule
- A small spot, usually under 10 mm. Extremely common in lungs and thyroid, and the overwhelming majority are not cancer.
- Progression / recurrence
- The words used when cancer has grown or come back. If these appear, the report is normally discussed with you rather than left to be read alone.
Blood tests and tumour markers
Routine bloods in follow-up usually include a full blood count, kidney and liver function, and sometimes calcium, thyroid or vitamin D depending on your treatment. They are as much about the effects of treatment as about the cancer.
Tumour markers are substances measured in blood that can rise with certain cancers — for example PSA in prostate cancer, CEA in bowel cancer, CA-125 in ovarian cancer, AFP and beta-hCG in testicular cancer. Their usefulness varies enormously by cancer type. For some they are central to follow-up; for others they are unreliable enough that guidelines advise against routine testing.
- Markers are interpreted as a trend over several tests, not as a single number.
- They can rise for benign reasons — inflammation, infection, smoking, liver conditions, and in some cases nothing identifiable.
- A normal marker does not exclude recurrence, and a slightly raised one usually prompts a repeat rather than an immediate scan.
- Ask which markers apply to you, what your baseline is, and what change would actually prompt action.
Practicalities worth knowing
- Ask when and how you will get results, and who will explain them. Not knowing is the worst part for most people.
- Ask whether you can book scans and results close together — a long gap between them is a fortnight of waiting for nothing.
- If you are claustrophobic in MRI, say so in advance; there are practical options and, occasionally, medication.
- Bring previous imaging details if you are seen in a different hospital — comparison with the old scan is what makes "stable" possible.
- Keep a note of what scan you had, when, and what it showed. My Journey keeps this on your own device.
What to ask your healthcare team
- What is this scan or test looking for, and what would change my treatment?
- When and how will I get the results, and who will explain them?
- If something indeterminate is found, what happens next?
- Do tumour markers apply to my cancer, and what is my baseline?
- Is there an alternative to this test if I find it difficult — for example an MRI instead of a CT?
- How much radiation does this involve, and does that matter given the number of scans I have had?
Save questions to My Journey so you have them in the room, or use a ready-made list.
When to seek medical advice
Contact your healthcare team if you have:
- Results that were promised and have not arrived — chase them rather than assume no news is good news.
- A reaction after contrast: rash, itching, or feeling unwell in the hours afterwards.
- Any new symptom while you are waiting for a scan — it may change what is scanned.
Get emergency help the same day if you have:
- Difficulty breathing, facial or throat swelling, or collapse after a contrast injection — emergency help immediately.
If you are worried and unsure, contact your team anyway — they would far rather hear from you unnecessarily than late. What to do in an emergency.
Common questions
What does "no evidence of disease" mean?
It means nothing on that scan or test looks like cancer. It is a statement about what the test can detect, not a guarantee that no cancer cell exists anywhere — which is why follow-up continues.
Does a raised tumour marker mean the cancer is back?
Not on its own. Markers can rise for benign reasons and vary between tests, which is why they are read as a trend and usually repeated before anything else is done. Their reliability also differs a great deal between cancer types.
Is an indeterminate nodule serious?
Usually not. It means the radiologist can see something but cannot classify it from that image. The standard response is a repeat scan after an interval to see whether it changes — most do not.
Sources
This page was written from the guidance below and checked against it on . Links are re-checked at each review — see our editorial standards.
- National Cancer Institute (US). Follow-up medical care after cancer treatment
- ASCO (Cancer.Net). Survivorship
- National Comprehensive Cancer Network. NCCN Guidelines for Patients
- Cancer Research UK. Coping with cancer
- European Society for Medical Oncology. ESMO patient guides