Non Hodgkin's Lymphoma
Cyberfamily
Diagnostic Imaging
Your doctor may order a variety of different diagnostic scans and tests to help monitor and diagnose your NHL. The variety of different scans is often confusing to patients, and many wonder why they are not getting one type of scan instead of another. The most important point to remember is that each type of scan has its purpose and place in treatment. No one scan type is superior to all the others because each serves a different purpose, and each is very valuable in its own right.
X-Ray
X-rays are the oldest type of diagnostic scan around, and they have been around since the late 1890's. X-ray images provide the doctor with an excellent image of the interior structures of the body. X-ray images 2 dimensional and are excellent for a variety of tasks, so they are the most widely used scan used in medicine in general. X-ray images are less useful in the diagnosis and monitoring of cancer because it does not provide enough 3D detail for monitoring. X-rays are very good for detecting fluid build up in major organs like the lungs ( pleural effusion ) Overall X-rays will not be a common choice for regular NHL monitoring or diagnosis.
CT scans
CT or Computed Tomography (often called CAT for Computed Axial Tomography) is the most common and useful type of scan for regular detection and follow up of NHL. CT's are still just X-ray images but they produce a near 3D image of the interior of the body. They do this by having the scanner spin around the body taking multiple pictures, or slices. A computer combines these images into a single image that looks like a slice taken right out of your body when looking down from the top of the head.
Click here to view a complete CT scan series
CT's are the most widely used scan because they allow the radiologist and doctor to look "inside" your body and see the structures that are there. They can see shape, size, and location of anything inside you. They provide far more detail than a simple x-ray image can. This is extremely important for finding tumours, and monitoring their growth, and seeing if they are threatening any nearby organs. Virtually all patients will undergo multiple CT scans throughout their journey with NHL. They are relatively inexpensive and give the doctors a great deal of information about what is going on. Even very small tumours can usually be spotted on a CT scan by an experienced radiologist. Since they have been around for a long time, there is a high degree of experience with them in the medical field so mistakes are less likely to happen.
PET scans
PET scans have been generating a lot of interest in the past few years. PET scans are quite different from CT scans and serve a completely different purpose. Many patients are under the very mistaken belief that PET scans are "better" than CT scans, but this is just not true at all.
PET scans detect metabolic activity in your body. This is accomplished by injecting you with a radioactive sugar substance called FDG (18F-fluorodeoxyglucose). Any area in your body that is undergoing a high rate of metabolic activity will absorb FDG quite readily since it contains sugar which provides energy for rapid growth. The PET scan works by detecting where the radioactive FDG is accumulating in your body and making an image of it. Many parts of your body will "light up" on a PET scan because many parts of your body are highly metabolically active. One example is 
your heart which is consuming all kinds of energy (sugar) to keep it going. But cancer cells also have a strong appetite for sugar and they will also light up very noticeably on a PET scan. A trained radiologist will know the difference between normal tissues that show up on the PET scan and abnormal tissues which indicate trouble. In addition to NHL PET scans are used for a variety of other health conditions.
Click here to see what a PET scan looks like (and a combined CT/PET)
Here is another excellent view of a PET scan
PET scans are superior to CT scans for detecting active cancer versus scar tissue. But this is one of the key reasons why both scans are so important. A large mass of scar tissue will not show up on a PET scan but will show up quite readily on a CT. On the other hand a small hidden mass of actively growing cancer may not show up on a CT scan but will show up very well on a PET scan.
PET Scans are most useful for those patients with intermediate or aggressive forms of NHL. In these patients it is critical to detect relapse or residual disease at the earliest possible point. Furthermore the use of PET scanning can help doctors determine the appropriate treatment. If the PET scan shows far less activity than was believed, then they may be able to choose less aggressive chemotherapy or less invasive surgery than planned. Likewise more activity than expected can indicate the need for a more aggressive treatment plan.
Those who have low-grade or indolent forms of lymphoma will benefit less from the use of PET. The slow growing nature of these types of NHL means that the tumours are not growing quickly and thus are less likely to attract the glucose. While most types of indolent lymphoma will show up to some extent on a PET scan there are some types which will fail entirely to show up. The important point though is that indolent lymphomas are generally only treated when the tumour burden begins to impact the quality of life, or threaten major organs. These conditions are easily detected by the patient (quality of life) or the CT scan (threatening major organs) so the cost of a PET scan can't usually be justified. Furthermore the PET scan is unlikely to change the treatment course so its value in low-grade lymphomas is limited.
A more recent advance is the combination CT and PET scanner. This machine does both types of scan at the same time, which is far more cost effective. It also allows the radiologist to combine the images for a more detailed view of what is going on. Click the first link above to see combined CT/PET images.
The following is the published practise guidelines by the National Comprehensive Cancer Network (USA) The information about PET scanning in lymphoma starts on page 18
NCCN Task Force Report: PET/CT Imaging in CancerA detailed look at Positron Emission Tomography
PET scans in the staging of Lymphoma
Can PET distinguish between indolent and aggressive NHL?
False positive PET scans with mediastinal lymphoma
Use of Positron Emission Tomography for Response Assessment of Lymphoma
Gallium scans
Gallium scans are very similar to PET scans. In fact due to the superiority of PET at detecting the smallest traces of cancer Gallium is quickly being replaced by PET as the scan of choice. Like PET Gallium is a radioactive substance. Tissues that are infected, or are cancerous have a very high affinity for Gallium and therefore it migrates to those tissues. This is often referred to as Gallium avid tissue. When the scan is performed those areas will light up quite vividly on the image. In general the patient will have the Gallium injection one day, then come back 3-4 days later for the actual scan.
Once again, Gallium scans have their place in diagnostic imaging so even though PET are considered superior there are times when a Gallium scan is the preferred scan. Gallium is very good at finding inflammation and infection. That combined with the fact that there are many professionals with more experience with Gallium Scintigraphy makes them a very useful tool.
MRI scans
Information coming soon (Not used often for NHL)
How much radiation am I getting from all these scans?
Looking for more information about the various types of scans? There is a ton of it on the Internet. Just use your favourite search engine to search for "FDG PET", or "Gallium Scintigraphy" or "Computed Tomography". You'll find lots of information.
One question that might occur to many patients is "Just how much radiation do I get from these various scans?" Of primary concern are X-rays, and CT's since they deliver radiation directly to your body. PET and Gallium scans inject radioactive substances into your body, but in only the most minute quantities.
It is a tough question to answer, but there is no doubt that a CT scan delivers dramatically more radiation to your body than any type of x-ray. A CT of the chest and abdomen can deliver the equivalent of 300 chest x-rays in radiation. While that sounds very frightening it is important to understand that this is still a small amount of radiation due to the very sophisticated equipment in use today. However if you are interested in reading a bit more about various radiation doses you get on a regular basis click the links below.
Ask the Expert - Medical radiation exposure
The FDA webpage "What are the risks from CT scanning"
Radiation and Risk. How much radiation do we get?
Radiation doses from typical nuclear medicine radiography
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