Introduction
Computed tomography, CT scan
is a diagnostic imaging procedure that uses X-rays to construct 3D images of the
body. The volume of the object has attenuation coefficients of x-ray
measurement which reconstructs the cross sections. X-ray irradiated the image
of the object that is reconstructed from a great number of readings of attenuation coefficient. All the date
collects together from the elementary volumes of object through the detectors.
The elementary surfaces of reconstructed image present on the screen of
computer from the projection of data matrix reconstruction which attenuation
coefficients affect the tone. A contrast dye is used to create a clearer image
on the screen. CT images of internal organs, bony structure, blood vessels and
soft tissue provide better feature, especially soft tissue and blood vessels of
the organ than traditional x-rays. There are 3 method of image reconstruction,
back method, iterative, method and analytical method. There are 2 type of
motion of x-ray beam relative to patient’s body. First is movement of the beam
around the body. Second is the movement of beam along the length of body.
CT scanners bombard the human
body with x-ray beams. The detector at the opposite side of the x-ray beam
collects the image of the body section when the emitter of x-ray rotating
around the patient. The image is taken from
many angles over the patient in one complete rotation. X-ray tube rotates continuously in one
direction due to the development of slip ring technology and contributes the
development of helical CT.
Fan-shaped beam of x ray produces a
narrow when it passes through a part of the patient’s body .The calculation of
attenuation coefficient is to measure the density of the tissue when the x-ray
beam passed by .
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The number of dose indicates
the quality of the image resolution. The reduces in dose, increase the pitch by
increases the table speed caused a decreases in image revolution. The range of
effective doses is 1 to 10 mSv predicted by diagnostic CT scan . The product of
millisievert (mSv) is calculated the
radiation exposure to the patient and estimate the risk of radiation dose, as
known as absorbance dose.The dimension of the body part
examined , the kind of procedure, and the type of CT apparatus and its process
effect the radiation dose produces.
Discussion:
There are many benefit of computed tomography
scan. CT is able to capture image of brain, bony structure, soft tissue and
blood vessel at the same period. Fast image speed cause higher
image revolution and less motion artifact .CT scan usually complete in 5 min
and MRI needed about 10 minutes to 2 hours. MRI is more sensitive to the
patient than CT scan. Allergic reaction is rare occurs due to iodine covalently
bind to non-ionic iodinated agents. (Nikhilesh
Jasuja,2015)
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The NLST found that 15 to 20 percent lower risk of dying from lung
cancer to the participants who received low-dose helical CT scans than who received standard chest
X-rays. Three fewer
deaths per 1,000 people screened in the CT group compared to the standard chest
x-ray group (17.6 per 1,000 versus 20.7 per 1,000, respectively). 24.2 percent
of the low-dose helical CT screens were positive but chest X-rays has
6.9 percent positive. Low-dose helical CT detected squamous cell carcinomas and
adenocarcinomas lesser frequently at the earliest stage than chest x-ray. CT
scan save up to 20,000 patients per year.(Robert Glatter,2015)
There are several disadvantage of CT scan. CT
scan pose the risk of emit radiation. Radiation exposure brings the risk of
cancer such as leukemia, lung cancer and brain cancer. Pregnant women are not recommended for
CT scan. Baby in the uterus is in risk. CT give greater amounts of
radiation to a developing pregnancy through the study of abdominal and pelvis.
Mother should not breastfeed their baby within 24 hours indicated intravenous
contrast. Children are more sensitive to radiation and should always be done
with low-dose system. (radiologyinfo,2014)
During CT examinations, diagnostic X-ray
investigations constitute 20% of total dose to patient, even if CT scan only
creates 4% X-ray investigations. It might be due to the growing total of CT
scanners in process. The decrease in the time to perform and reconstruct the
image, increase the number of slices per patient. Therefore, decrease in the
dose per slice in order to enhance the image quality, quantum noise should be
reduced. The increase in the irradiation of patient is due to these reductions.
In late eighties of United Kingdom, the CT examinations were abdomen, chest and
pelvis and head as well. Their relative frequencies and effective doses are
listed in table 1. (Mikael,1995)
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Every 270 middle-aged women who undergo
CT coronary angiography there is 1 woman might get cancer. CT coronary
angiography is a high-dose diagnostic process that repeated scanning heart
vessels after injected contrast dye. Smith-Bindman says, young people have
higher risk to have cancer because cancer cell have enough time to develop
after a carcinogenic exposure. Middle-aged women have double lower risk of
getting cancer than the women who is 20.
One in 300 chance of a CT scan contributing to a cancer longer period of
time in which additional doses of radiation could lead to a
cancer.(Robert,2014)
As compared to the radiation
emitted from CT scan causes fatal cancer with the natural incidence, the chance
of a fatal cancer increased by 0.05 % in U.S. Radiation of CT scan causes
cancer at about 0.4% of all cancers in U.S.
Growing 20 to 20.05 percent of fatal tumor develop after a single CT
scan. Human body absorbs 150 to 1100 times radiation from x-ray during a CT
scanning, or absorb around a year of radiation from both natural source and
artificial source in the environment. (Carina, 2013)
The authors observed that CT irradiation
affected 37 out of 41 implantable cardiac rhythm management devices (ICRMDs).
Seventeen ICRMDs were affected at classic clinical doses and 20 at optimum dose
levels CT scanner. The investigation was carried out by using a 16-slice and a
64-slice. X-ray dose is very high may cause the irreversible damage to the
patient. The effects on the ICRMDs can be observed, when the x-ray beam was
straight over the devices .The newer scanners designed for faster scans may
cause CT scanner interference on implantable electronic devices. Increases the
x-ray dose to increases faster scans times. The increase in dose rate could increase
such interference. (McCollough ,2007)
Conclusion:
Computed tomography scan does bring a lot of
benefit to patient by construct a 3D image of internal organ. It does help
doctor to determine the tumour, damage of blood vessel and bone. However, CT
scan emits radiation to patients who undergo scanning when the x-ray beam
rotates around the patients and contribute the image. In my opinion, CT scan
should be ban in medical field since it will irradiate and causes a severe
damage and cancer to the patient. There is other scanner can replace CT scan
such as MRI which does not using x-ray to contribute image even it took longer
time .
Bibliography
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