1.
INTRODUCTION
A CT scan is a computerized
tomography scan. It uses x-rays and a
computer to create detailed images of the inside of the body which provide
exceptionally clear views of internal organs by combining data from multiple
x-ray images. Of all the internal
imaging procedures available, CT scan is the most detailed. CT scan examination is useful and widely used
in diagnosing cancer. The CT scan
procedure in noninvasive and painless, and also quick and convenient for most
patients and most systems can be scanned, from brain to leg.
Because of advances in computer
technology, CT scan now much faster than in the past and this improved patients’
comfort. These improvements have also
led to higher resolution images which help doctors to visualize small nodules
or tumors which cannot be seen with a plain film x-ray.
However, there are also disadvantages
of CT scan. CT scan deliver a relatively
high dose of radiation to the patient compared to other diagnostic tests. For a single scan this is not a problem, but
for patients who need to undergo repeated tests, this can be a problem
subjected to a significant level of radiation, increasing their cancer risk.
In most cases, CT scan procedures
are safe and many think that the benefits of having a scan outweigh any
potential risks. Even though CT scan
does expose patient to radiation, the amount of dose is actually small and will
not cause any harm. However, CT scans
until now is still not recommended for pregnant women because many researchers
suggested that there is a small risk that the x-rays used could harm the unborn
baby. As for children, CT scan will only
be recommended if a child has a serious condition that puts them at greater
risk only because children are more at risk than adults are from developing a
build-up of radiation.
CT scan only provides images in
shades of grey. Because the shades are
similar, making it difficult to distinguish between two areas. This is when contrast enhancement is needed
to overcome this problem. Contrast
enhancement used is gastrografin and contrast media. Gastrografin is commonly used to outline the
gastrointestinal tract via rectal and oral.
Intravenous contrast media is used to outline arterial blood vessels. Most patients that undergo CT scan will need
to get a contrast injection. This is to
help distinguish normal tissues from abnormal tissues and also helps to
distinguish blood vessels from other structures such as lymph nodes.
2.
LITERATURE
REVIEW
Researchers reported that widespread
overuse of CT scans and variations in radiation dose caused by different
machines are subjecting patients to high radiation doses that will lead to ten
of thousands of new cancer cases and deaths (Maugh, 2009). Each year that today’s scanners are used,
14,500 deaths could result. Maugh (2009)
noted that when healthy people are exposed to the radiation, the imaging may
create more problems than it solves.
Lee and Chhem (2010) noted that the
increasing use of CT has sparked concern over the effects of radiation dose on
patients, particularly for those who had repeated CT scans. The effective dose from a CT scan on average
is ∼10mSv. CT scan has consistently been found to result
in higher effective dose than other medical imaging procedures and cardiac CTA
and whole organ CT perfusion studies are among the highest dose studies of medical
imaging procedures (Lee and Chhem, 2010).
Brenner (2011)
reported that CT scans are the most important contributor to the estimated
worldwide collective effective dose from diagnostic imaging with approximately
4 million people-Sv per year. However,
there have been significant technological advances in reducing the dose per
scan and it can be done by adjusting the MAs setting manually for individuals
of different sizes or by automated current modulation (Brenner, 2011).
Recent research,
Wesolowski and Lev (2005) noted that successful attempts have been made in
pediatric radiology to decrease dosages by lowering milliamperage based on
patient age and body weight. Within the
area of neuro radiology, work has also been done to limit dosage imparted
during CT examination of brain, especially in regard to those undergoing
multiple studies, also by decreasing the milliamperage in a manner that does
not degrade image quality (Wesolowski and Lev, 2005).
Chou et al.
(2011) said that their study show persistent renal enhancement at non-contrast
CT is loosely associated with a higher risk for developing contrast-induced
nephropathy. However, Chou et al. (2011)
noted that the increased frequency and striking appearance of delayed renal
enhancement in patient who received intra arterial versus intravenous iodixanol
is multifactorial and also relates to high contrast material dose, short time
until CT imaging, high baseline renal function, and other predisposing factors.
Recent research
from Nazim et al., (2011) found that with the advancement and widespread use of
CT imaging techniques, the proportion of incidentally discovered tumors in
asymptomatic individuals have risen steadily where the statistic show
incidentally discovered tumors were only 10 percent in early 1970s but is has
risen to 60 percent in 1990s. Nowadays,
multidetector row CT has been a major advancement in imaging which provide thin
slice collimation, high speed of acquisition and allow reformatting of imaging
in any planes which can provide excellent anatomical details (Nazim, 2011).
According to
Tabibian et al. (2011), the latest generation of CT scanners is continuing the
developmental efforts toward improving tissue characterization, spatial and
temporal resolution, and image analysis and also being directed at improving
functional CT capabilities, lowering CT contrast agent usage, utilization of
novel contrast agents in CT applications, and achieving the lowest possible
radiation doses.
Verdun et al.
(2007) noted that one problem in CT that requires closer study, especially with
the continuous increase in the size of the beam collimation, is the length of
the over scanning of the acquisition where this length represents the exposure
of anatomy that is not to be imaged, but that is required to reconstruct the
first and last slices of the volume investigated.
In one study
where the researchers want to determine the impact of a reduced 100 kV tube
voltage on image quality and radiation exposure, Bischoff et al. (2009)
concluded that reducing the CT angiography cardiac tube voltage to 100 kV in
non obese patients is associated with a significant reduction in radiation
exposure while maintaining diagnostic image quality. Thus, the researchers suggested that the 100
kV scan technique should be considered for CT angiography cardiac dose
reduction in adequately selected patients.
Recent research,
Sorantin et al. (2012) noted that the most recent developments like the 320 row
detector facilitate volume CT helps to avoid the over beaming effect of helical
scanning and thus significantly contributes to dose minimization for pediatric
CT, additionally speeding up the investigation and decreasing sedation needs
and duration. For example, in children
the neck is relatively short, therefore the 16 cm detector can cover the entire
area using the volume mode which is one single rotation without any pitch. Furthermore, in small infants the entire
chest can be scanned by a single rotation of the 16 cm detector, thus allowing
ultrafast scanning (Sorantin et al., 2012).
Other than all
this, in new advanced of CT technology, Yang et al., (2006) stated that cone
beam CT scan provides a new method to acquire the 3D images of teeth in living
individuals and by using this 3D images the ratio of tooth volume can be
calculated. According to Yang et al.,
(2006), the presented research shows promising results for age estimation based
on tooth volume ratio. The newest cone
beam CT modalities and optimization of the ratio measurement software can
therefore make the technique mature in forensic odontology research.
Now, there is
also modern CT acquisition and 3D conversion, combined with the direct laser
metal forming (DLMF) process, allows the fabrication of custom made, root
analogue implants, perfect copies of the radicular units that need replacing
(Figliuzzi et al., 2012). This report
demonstrates the successful clinical use of custom made, root analogue DLMF
implant. In their experiment, result
shows at the one year follow up examination, the custom made implant shows
almost perfect functional and aesthetic integration.
3.
DISCUSSION
3.1 Issues Related to CT Scan
Today whole body CT scans are common
among healthy patients to look for hidden tumors or other illnesses even though
they rarely find anything wrong. By
exposing healthy people to radiation, the scans can create more problems than
they solve (Maugh, 2009). However, many
researchers agree that when the screening is used for diagnostic purposes, the
benefits outweigh the risks. Even though
manufacturers design instruments that use lower doses of radiation, but many
older machines rely on higher doses.
Moreover, many diagnostic centers cannot afford to purchase new CT scan
machine that use lower doses of radiation.
Furthermore, machine settings for particular procedures are not
standardized, and individual radiologists use the technology differently for
different patients, leading to wide variance in doses delivered to the
subjects.
Noted that
the use of pediatric CT is rapidly increasing in frequency and probably more so
than for adult CT. Verdun et al. (2007)
reported that one has to consider that for a given effective dose, a child is
more likely to develop a malignancy than a 50 year old adult and one pass
through the abdomen of a young girl results in a risk factor of 10_3. Although this risk factor remains small for
an individual when it is balanced by a medical benefit, researchers noted that
the use of CT becomes a public health issue when the small individual risks are
multiplied by the number of procedures performed each year.
There are also some issues raised regarding
that CT scans being undertaken when they may not be clinically helpful. Brenner (2011) noted that it is likely at
least 25 percent of CT scans fall into this category where actually it can be
replace with another alternative imaging modalities or could be avoided
entirely. This issues happen at some
local hospital in Malaysia where the consultant unnecessarily request for CT
scan examination for some particular case but according to radiologist that
particular case actually need not do under CT examination where plain x-ray
itself can show the diagnosis very well.
Most of CT scan cases need IV
injection of contrast media. The problem is if patient have history of kidney
problem that cause urea and creatinine level high, injection of contrast media
is not recommended. However, for
emergency cases like pulmonary embolism, the embolism cannot be seen without an
IV injection. Because of that, now the
manufacturer produce one contrast media that is save for patient with kidney
problem, the visipaque 320. Visipaque
320 is a isoosmolar or isotonic contrast medium. Barrett et al. (2006) suggested that isotonic
contrast media may have better renal tolerance in high risk patients compared
with low osmolar contrast media has had considerable impact in the scientific
community. Low osmolar contrast media is
Iopamiro 370 which is used for patient with normal creatinine level. Until now, more studies done on regarding
this contrast agent, and one of study from Kuhn et al. (2008) pointed that there
is no significant different in incidence of contrast induced nephropathy in
patients with chronic kidney disease after CT scan using contrast medium
Iopamiro 370 and Visipaque 320. Because
of this, when contrast media is really needed for diagnosis during CT scan,
radiologist usually asked to proceed the scan with an injection only if patient
or patient relative agree with it and will suggest for hemodialysis after scan or
flush with 1 pine of saline.
Another issues regarding contrast
media used during CT scan is allergic reaction and extravasations. Even though contrast media are usually safe,
severe or life threatening reactions can occur.
If patient is allergic to contrast media, the reaction will occur
immediately after an IV injection. The
reactions include patient could be sneezing nonstop, the skin will turn red or
sometimes rashes appear, and patient will have difficulty in breathing. This is when radiographer and radiologist should
be aware and be prepared to manage it.
Usually patient will be injected with one drug name hydrocort 200 mg and
patient will be observed or be pushed to emergency department. Extravasation can occur mostly by using power
injection of contrast media. The
elderly, infants, children, patients with altered consciousness and those with
underlying vascular disease are more prone to extravasation (Singh and Daftary,
2007). The only option to solve the
extravasation is by elevating the hand and applied cold compression.
The early and accurate diagnosis of
injuries is important for treating trauma patients. Almost all the time the consultant will
request CT scan for diagnosis especially CT brain for trauma patient. But CT scanning is actually time-consuming
due to technical and logistic reasons.
The issue is in many hospitals here, CT scanner is not located in or
near the emergency department, but it is located at the x-ray department and
far from emergency department and this will require patient transfer and in
house transport. This could lead to
delay in diagnostic information and treatment decisions. According to Jin et al., (2009), because of
this several centers have attempted to shorten these delays by moving the CT
scanner into the emergency department itself.
Other than that, with the increasing role for CT scanning in trauma
patients, CT scan usage will increase in a group of patients that arrives at
unexpected moments. This can interfere
the flow of CT scan waiting list and with other patient care, since trauma has
the highest priority and will lead to extended waiting times and overtime for
patients and personnel. To anticipate
for this trend, most centers have adjusted their planning to facilitate for
unexpected CT scanning for trauma patients and some large centers invest in
extra CT scanners (Jin et al., 2009).
3.2 Advanced In CT Scan
Nowadays, the automated techniques
to reduce the dose per CT scan are now built in to most of the newer CT
scanners. Radiographer can manually
adjust the mAs setting according to patient size or just click ‘on’ to dose
reduction button where it will automatically reduce the dose given to the
patient during scan without reducing image quality. This is especially important for children and
to patient who have to come for CT scan annually for follow up or
restaging.
Tabibian et al. (2011) pointed that
the use of cardiac CTA studies has increases 223 percent worldwide in the
Medicare population from year 1996 to 2005.
In Malaysia, most of hospital use 64 slice and 128 slice CT scanner
which can provide imaging protocols for CT cardiac. However, this multislice CT scanner only can
provide good image of coronary arteries if the patient can tolerate well where
patient need to hold breath and not move for at least 15 seconds during
scanning. Even though most of patients
can put up with this, there still many patients where the scanning cannot be
proceeded due to patient cannot hold breath that long and some patient is
anxious on table. To solve this issue,
the manufacturers come up with one new advance technology of CT scan where it
is able to cover the whole organ in a single rotation. This faster scan times can reduced motion
artifact and patient need not hold breath that long.
Another development and advance in
CT scanning is regarding stroke imaging.
Earlier days CT images can only rule out hemorrhage or tumor as the
cause of a patient’s symptoms. After
that, faster axial or single slice helical image acquisition allow consultant
to see the immediate and chronic effects of ischemia and infarction. But now multislice scanning can provide
detailed depictions of cerebral blood supply and perfusion scanning allow to
see the effects on brain parenchyma directly.
Lobo and Antunes, (2012) noted that
recent advances in CT technology with multi detector equipment which widely
available in many centers, allowing a highly detailed evaluation of chest in a
short time period has resulted in expanding indications of chest CT in
pediatrics patients. Improved in
diagnostic means increase number of CT examinations in children which brings to
issue on radiation dose. However apart
from dose, there are many other advantages of this advances CT technology for
pediatric patients. There are some
problems related to children that usually are not encountered in adults which
may interfere with the quality of CT examinations, such as lack of visceral fat
and mostly is patient motion. To prevent
motion, most children need to give sedation during or before the start of CT
examination which is time consuming. This
newer technology which provides faster scanners, allow a more exquisite
technique with lower rate of sedation, greater optimization of intravascular
contrast and less image deterioration from respiratory artifacts in non
cooperative children (Lobo and Antunes, 2012).
Another advanced in CT scans is the
use of 3D reconstructions of spiral CT in the musculoskeletal system. It is beneficial to patients in whom CT is
desired to delineate the presence and extent of congenital anomalies, traumatic
injury, tumor, infection and inflammation.
It also has specific role in postoperative evaluation, especially when
the results of plain x-ray fail to answer the doubts of the orthopedic surgeon
regarding satisfactory alignment of complex fractures (Alam and Chander,
2005). 3D CT imaging also is able to
compensate for streak artifacts due to the presence of metallic implants such
as plates, pins, and prostheses.
The latest
generation CT scanners offer some decisive advantages especially regarding
examinations of moving structures like thorax and the heart. With this latest CT scan, it is also possible
to perform whole body scans extremely fast nowadays. For example, a person with a height of 198 cm
can be scanned in less than five second (Paul et al., 2011). Until now, such whole body examinations are
taking more than ten minutes to be performed starting from patient preparation
to diagnosis.
Recent research,
noted that advances in multi detector CT technology have further changed how
radiologic investigations are utilized in the diagnosis and management of small
bowel Crohn’s disease. This is important
because radiologic imaging studies are the only non-invasive method available
for evaluation of the small bowel.
Primarily, CT enteroclysis provide valuable information on staging,
evaluation of possible small bowel obstruction, as well as demonstration of
fistulae and abscesses. Secondarily, CT
enteroclysis plays a role in screening for patients with obstructive symptoms
prior to capsule endoscopy, which is now increasingly used to diagnose early
small bowel Crohn’s disease (Kohli and Maglinte, 2009).
Another advanced
in new CT technology is there is dynamic volumetric acquisition protocol. Dynamic studies can be acquired easily by
scanning the same anatomical region several times. Example of this anatomical region is head,
where blood flow dynamics can be assessed and quantified with perfusion
software. Other example is in orthopedic
region, where dynamic movement of joint can be observed by performing scanning
during patient motion. Other than that,
one can observed lung function during free breathing and as for angiographic,
blood flow can be observed during the injection of contrast.
4.
CONCLUSION
CT scans have revolutionized health
care by improving the life and health of its patients that allow the human body
to be studied and examined to detect the sign of most major illnesses. The CT scan machine’s procedures are easy to
comprehend, and there are possible improvements that can be made in order for
future patients to have less trouble with breathing or moving during the scan
by allowing patient to be more flexible, not rigid yet producing better, faster
and yet more accurate results during the diagnose.
Because of all the issues raised
regarding CT scan, scientist, inventors and manufacturers had produced new
machines with new advanced CT technology where it can solve most of the problem
faced. This new technology designed to
improve patients’ care through new clinical examinations, with lower contrast
medium dose and exposure dose. This
technology enables faster and more accurate diagnosis and provide highest
quality diagnosis outcome. This new
scanner is called Aquilion One.
Even though helical and multislice
imaging already built great milestones in the history of CT scan, Aquilion One
offers the next leap forward in CT technology that will revolutionize patients’
care. Aquilion One is both the latest
step in the natural progression of multislice imaging and a quantum leap that
will carry CT imaging into the future.
Clinicians have long dreamed of being able to acquire isotropic volumes
of an entire organ with a single rotation of the gantry. This leap is possible only with Aquilion One.
5.
RECOMMENDATION
All
centers in Malaysia should prepare a standard operating procedure as guidance
for practitioners based on the balance of risk and benefit involved in the CT
scanning procedures concerned. Any scan
process that a patient undergoes should balance the clinical benefits against
the risks of radiation involved.
Today especially in private
hospitals in Malaysia, consultants like to take advantage from patients who
have medical insurance by insisting for CT examination even though it is not
necessary. This should not happen. If CT is not the modality of choice for
diagnostic purpose, then it should not be made available for the assessment of
asymptomatic individuals. This is to
reduce unnecessary radiation dose and contrast dose give to patient.
Other than that, quality control
procedures should be implemented to ensure that dosing protocols are followed
every time and the planned amount of radiation is administered. If more than one study is performed on a
patient during one imaging session, radiographers should adjust the dose of
radiation so that it is appropriately safe for each study.
6.
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