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Why your doctor might recommend a PET/CT?
CT scan
MRI
4 Difference between ct scan and MRI
MRI gives higher detail in soft tissues. One of the greatest advantages of MRI is the ability to change the contrast of the images. Small changes in radio waves and magnetic fields can completely change the contrast of the image. Different contrast settings will highlight different types of tissue.
For purposes of tumor detection and identification, MRI is generally superior. However, CT usually is more widely available, faster, much less expensive, and may be less likely to require the person to be sedated or anesthetized.
Bones are virtually void of water and therefore do not generate any image data. This leaves a black area in the images. MRI scanners are best suited for imaging soft tissue.
CT scans are widely used in emergency rooms because the scan takes fewer than 5 minutes. An MRI, on the other hand, can take up to 30 minutes. An MRI typically costs more than a CT scan.
Cost. CT Scan costs range from $1,200 to $3,200; they usually cost less than MRIs (about half the price of MRI). MRI costs range from $1,200 to $4,000 (with contrast), which is usually more expensive than CT scans and X-rays, and most examining methods. Time taken for complete scan. Usually completed within 5 minutes.
CT, Computerized Axial Tomography, uses x-rays to generate images of the body, including bone. In the CT scanner the x-ray tube, (source) rotates around the patient laying on the table. On the opposite side of the patient from the tube is the x-ray detector. This detector receives the beam that makes it through the patient. The beam is sampled via some 764 channels, (approximate number of channels). The signal received by each channel is digitized to a 16 bit value and sent to the reconstruction processor. Measurements are taken about 1000 times per second. Scan rotations are usually 1 to 2 seconds long. Each view/channel chunk of scan data is compared to calibration scan data of air, water and polyethylene (soft plastic), previously acquired in the exact same relative location. The comparisons allow the image pixels to have a known value for a particular substance in the body regardless of differences in patient size and exposure factors. The more samples or views, the better the picture.
For more information, see this video, which further discusses different types of imaging scans, including the ultrasound, CT scan, MRI, and PET scan .