<b>Spiral CT Scans</b> 
are very sophisticated X-ray examinations.  They support faster, higher-quality image acquisition with less radiation exposure, typically eight to 10 times faster than conventional CT scans, and can usually be obtained during a single breath hold, and increase the rate of lesion detection.

CT [Computerized Tomography] scanning works very much like other x-ray examinations in that controlled amounts of x-ray radiation are passed through the body, and different tissues absorb the radiation at different rates. With CT, X-ray film is replaced by an array of detectors, which measure the x-ray profile emerging from the body that is being scanned. When the computer reassembles the image slices, the result is a very detailed, multidimensional view of the body's interior. You might think of it like looking into a loaf of bread by cutting it into thin slices. 

CT scans are very good for lung metastases. CT is used as an overall screener, and is probably more cost effective than MRI for that purpose.  Since the two most worrisome places are liver and lungs for metastases, and CT performs excellently for lungs and reasonably well for the liver, it is a good choice.  CT scans picked up adrenal tumors, and they will show problems in pancreas, spleen, kidneys, and bowel.   If lesions are small, CT can miss them.  The size of the smallest tumor picked up by CT varies with the machine...later models do 1/2 cm cuts instead of 1 cm cuts, but tumors of up to a centimeter can be missed if they happen to fall between the cuts.

CT can miss a lot of pelvic pathology.  If your pelvis is a primary site, you might want to use ultrasound scans as well, and MRI if there are any suspicious lesions.  CT scans are not good for bone, nor are they good for brain imaging. MRI is preferred for suspected brain and bone lesions.  MRI is also the scan of choice for extremity lesions.  CT is generally better for things that move, like lungs and bowel.  See the section below comparing CT and MRI scans of the liver.

There are higher resolution, swifter scanning multi-slice CTs being developed. The use of a four row scanner offers various options -- a large volume can be scanned quickly (e.g. chest, abdomen, and pelvis in a trauma patient in 20 seconds) OR a smaller volume can be examined with much finer slices (e.g. 1 mm slices through the chest in 20 seconds, with much more detail.)  CT scans are reaching towards the ultimate they can achieve - better resolution, increased speed, and lower power consumption are areas under development. They are often the imaging tool that gave the primary cancer diagnosis, and often the main tool for surveillance for recurrence.  CT limiting factors for patient exposure remain radiation dose, and potential kidney toxicity from the injected iodinated contrast medium.  

A new combination of PET and CT scan, done at one sitting, will allow for correlation between metabolic activity [PET scan] and the more exact physical picture of a lesion [CT scan].  However, some of the early combination scanners may have reduced resolution compared to their single-purpose counterparts.

British researchers announced that they have combined CT scans and magnetic resonance imaging (MRI) to help better identify cancerous tumors.  Dr. Peter Hoskin, a clinical oncologist at Mount Vernon Hospital in Middlesex, southern England, who helped to develop the technique, said it will initially be used in prostate cancer patients, but it could be helpful in treating other tumors, particularly those in the pelvis, head and neck. Combination scanners are not yet widely available.

<b>EXCELLENT British Medical Journal Article on Computed Tomography in Clinical Practice</b>
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