Is a CT scan "tuned" for what you are looking for example bone or soft tissue abnormalities?

CT examination can be tailored to enhance the depiction of bone, not only through the use of bone windows as described above, but also by the use of specific filters - a bone filter will enhance fine detail and edge detection at the expense of increased image noise, which would be unacceptable in the evaluation of soft tissues. This said, if you have had CT imaging, it is possible to depict blood vessel calcifications that are related to atherosclerosis.  The significance of these calcifications are variable.  The best body of data has to do with the significance of coronary artery calcifications.  Sometimes, dense calcifications can be also seen to narrow important other important arteries providing supply to the brain, kidneys, and legs, for example. Radiologists are trained to review all body parts included on a given CT scan.   Your doctor can review your study, and can typically consult with a radiologist, if there are questions about any possible incidental findings that you may be concerned about.This answer is not a substitute for professional medical advic...

There are at least 3 stages at which variables can be modified, allowing a wide variety of tissues to be visualized for any given CT scan, but that doesn't mean that one type of scan covers all disease processes! 1) Initial planning (protocoling) and acquisition: decisions are made as to which type of scan is required, depending on the organs and type of disease being assessed. The variables include (but are not limited to) the region of the scan; the presence or absence and timing of intravenous contrast (a.k.a. dye); the type, presence or absence of bowel contrast; the radiation dose and related parameters, such as "pitch"; the number of phases of the scan (I.e. the number of ties the scanner will pass over the area of interest), reconstruction algorithm/kernel etc. Once the scan has been performed, the die is cast to a certain degree. For more information on CT protocols, which will give you an idea of how some protocols are vastly different from others, try looking under the heading of "Scanner Protocols" (on the left hand side) at http://www.ctisus.org. This is a wonderful resource a lot of radiologists use, run by Elliot Fishman at Johns Hopkins University. 2) Postprocessing: usually automated and defined by the elements decided on while setting the protocol. This is where the information is made into pictures for the radiologist to interpret. Many options and preferences exist. This is where we may choose to view the information reconstructed into several different planes or even curved planes. Surface shaded 3D reformats and angiography projections can be obtained. Thin cuts or thick MIPs (maximum intensity projections) can be made. Virtual colonography fly-through images can be reconstructed. A lot of this has to do with software. The raw data takes up a lot of hard drive space and can't be kept forever. If you want to add on any other reconstructions you have a limited time in which to do this. If, for example, I see a subtle brain lesion on a sinus scan (which usually has a computer reconstruction algorithm optimized for bone and soft tissue, not brain),I  have to make sure I get the recons done before the computer deletes the raw data. Until that time, however, all the information I need is available for manipulation. 3) Readout: the radiologist reads the images provided and can manipulate the "window" width and level to optimize visualization of the various tissue densities. For example, if I am looking at a head CT I look at it on windows optimized for visualization of the brain, then a "stroke window" that brings out subtle differences in grey-white differentiation, then a bone window (also good for assessing the included sinuses), then a "blood window" for intracranial hemorrhage, then a soft tissue window to make sure I have assessed the scalp, orbital contents, etc. Similarly for a belly scan I look at it on soft tissue, liver, air and bone windows. Plus I make subtle adjustments to better visualize any abnormalities I find. So, in answer to your question, you can tune the scan to assess the area of interest, but that doesn't mean you won't see anything else. Coronary calcium scoring CT is performed with a specific protocol, but we still notice if there is coronary calcification on any CT that covers that area of the body. We just can't apply a score to the finding because it's not visualized well enough. If you are doing a scan to assess for a pancreas mass you do a very specific protocoled examination. If you just do a "regular" generic body scan you will still see the pancreas and the tissues around the pancreas. Perhaps not as well as if you had optimized the scan to look at them, but with some degree of usefulness. There are some types of diseases or lesions which can, however, be completely missed if the protocol is not optimized to look for them. Some liver lesions can be very tricky to see unless the scan is timed exactly right. Similarly pancreatic mass lesions can blend into the background depending on when you scan the pancreas in relation to when the maximum concentration of contrast is in the pancreas. Some liver lesions have to be scanned in several phases to help differentiate them from one another, as the different types of lesions (i.e. metastases, primary liver cancer and various benign tumors) have different "enhancement patterns". The scans performed for blood vessel assessment have to be very carefully timed in order to be diagnostic. For example, pulmonary thromboembolism CT scans have to be timed nearly perfectly or else they are near useless. A good scan is optimized to answer a specific question and thus careful history and physical examination is STILL critical, possibly moreso when undergoing CT! The last thing you want is to have a scan twice (with twice the dose of radiation) because it wasn't optimized the first time.

Yes, CT scanners have various presets depending on what you want to see. This allows to adapt the dose to what is needed. That said, it's entirely possible that an unrelated exam can be used for something else. Why don't you ask your doctor?