Working of CT Scan

 

What is a CAT Scan or CT Scan?

     A CAT scan (also called a CT scan) is a noninvasive, painless medical test that helps physicians diagnose and treat medical conditions. CAT scans allow physicians to rapidly create detailed pictures of the body allowing them to more easily diagnose problems such as cancers, cardiovascular disease, infectious disease, trauma and musculoskeletal disorders. CAT scans may also be used to guide surgeons to the right area during a biopsy. CAT scans are one of the more common imaging technologies used by physicians to analyze the internal structures of various parts of the body. There are approximately 52 million CAT scan test performed each year making this one of the more common imaging technologies used by the medical field.

Why do CAT scan cost vary so much?

     CAT scan cost vary based upon the type of CAT scan you're getting (abdominal versus brain for example) as well as where you have the procedure performed. Similar to the price of a new automobile. Everyone knows that the "sticker price" is just an asking price. There's a nice mark-up included in that price and often if you ask the dealer to come off that price they will. Medical procedures are often no different. Most hospitals and imaging centers have a "sticker price" which are often on the high end. If you ask and work with most facilities they will often offer a substantial discount to individuals and insurance carriers due to the form of payment and the volume of procedures they pay for on an annual basis. There's more on this below so keep reading.

How does a CAT Scan work?

     CAT scans use special x-ray equipment to produce multiple pictures of the inside of the body. Software joins the pictures together in cross-sectional views for detailed examination. CAT scans can be used to view internal organs, bone, soft tissue and blood vessels. These scans provide greater clarity than conventional x-ray exams. Often a special dye, called contrast, may be ingested to further enhance the scan images and the various structural relationships of the areas of interest. so that specific areas inside the body are highlighted. CT scans are often used to defining the structural relationships of the spin, the spinal cord, and its nerves. CT scans are also used in the chest to identify tumors, cysts, or infections that may be suspected on a chest x-ray. CT scans of the abdomen are extremely helpful in defining body organ anatomy, including visualizing the liver, gallbladder, pancreas, spleen, aorta, kidneys, uterus, and ovaries. CT scans in this area are used to verify the presence or absence of tumors, infection, abnormal anatomy, or changes of the body from trauma.

Examination	Typicaleffective dose (mSv)	(millirem)	Real dose(mGy)[27]	Dose in number of years it would take the irradiated body part to absorb the same energy from background radiation	Dose in number of DNA double strand breaks that are induced per cell[11]
X-ray Personnel security screening scan	0.00025	0.025[28]
Chest X-ray	0.1	10
Head CT	1.5[27]	150	64	21	2.24
Screening mammography	3[19]	300
Abdomen CT	5.3[27]	530	14	4.6	0.49
Chest CT	5.8[27]	580	13	4.3	0.45
CT colonography (virtual colonoscopy)	3.6–8.8	360–880
Chest, abdomen and pelvis CT	9.9[27]	990	12	4	0.42
Cardiac CT angiogram	6.7-13[29]	670–1300
Barium enema	15[19]	1500
Neonatal abdominal CT	20[19]	2000

For purposes of comparison, the average background exposure in the UK is 1-3 mSv per year.

Radiation dose units

The radiation dose reported in the Gray or mGy unit is proportional to the amount energy that the irradiated body part is expected to absorb, and the physical effect (such as double strand breaks) on the cell's chemical bonds by x-ray radiation is proportional to that energy.
The volume weighted CT dose index (CTDI_vol) is used to report an absorbed dose in the Gray unit, that is proportional to the average of the energy that is absorbed by the body part, since the amount of energy that is absorbed is greater at the skin, and lower at the center of the body part.
The Sievert unit is used in the report of the effective dose. The Sievert unit in the context of CT scans, do not correspond to the actual radiation, that the scanned body part absorb, but rather to an other radiation level of an other scenario, in which the whole body is subjected to the other radiation level, and where the other radiation level is of a magnitude, that is estimated to have the same probability to induce cancer, as the CT scan.^[30] Thus, as is shown in the table above, the actual radiation that is absorbed by a scanned body part is often much larger than the effective dose disclose.
Note, that even though the stated objective of the effective dose is to report a whole body radiation value, that is proportional to the biological effect of the actual radiation, the effective dose measure the biological effect based on statistical studies of cancer rates in a population, that was exposed to radiation from a nuclear blast, and thus its fulfillment of its objective is questionable, due to the possibility that the biological effect of radiation from a nuclear blast is different, due to the fact that exposure to a nuclear blast during war is a psychologically traumatic event in itself, due to covering only one biological effect, namely cancer, and due to a very limited theoretical understanding.
The dose length product (DLP) is the multiplication of the CTDI_vol with the length of the portion of the body part that was scanned, and has the units of Gray*Centimeter. It is used, by multiplication with constants, to derive the effective dose, and cancer risk, that correspond to the irradiation of a portion of a body part, and can be used in other calculations, which include the multiplication, that the CTDI_vol include.