A rate……. Doctor checked for a weakened pulse, an

A 54-year-old African-Caribbean man who is 5’7 and weighs
198lbs, BMI of 31.01 which is classified as being overweight. He is a heavy
smoker, has a high-fat diet and high blood pressure. He has excessive amount of
alcohol and sedentary lifestyle which are all risk factors that increase
chances of atherosclerosis. Smoking can damage and tighten blood vessels,
contributes to high cholesterol levels and blood pressure. It doesn’t allow
enough oxygen to reach the body’s tissues as patients experienced shortness of
breath. Alcohol is risk factor due to damaging the heart muscle. He went to the
GP complaining with the following symptoms such as sweating, fatigue,
dizziness, light-headedness, nausea and numbness on the shoulder. He also
distressed tightening and squeezing pain in the chest.

The doctor reviewed patients’ medical history and asked
if he had any previous family history of heart disease, stroke or other
circulatory problems. The doctor then carried out physical examination to
measure the blood pressure and heart rate……. 
Doctor checked for a weakened pulse, an aneurysm which checks for
abnormal swelling or widening of arteries that can be because of faintness of
artery walls. The doctor also identified any slow wound healing which is signal
that blood flow is restricted. Blood test showed high levels of certain fats,
cholesterol levels… results of the tests

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The patient then would be referred to a Cardiologist to
carry out further investigation, due to the results of the above tests Coronary Artery Atherosclerosis would
be suspected. The most suitable imaging technique to make diagnosis would by
using CT Angiography (CTA). CTA is an examination that uses a dye and special
x-rays to identify the insides of arteries and can show whether plaque is blocking
the arteries and severity of the plaque (Nair and Devaraj, 2017).
A thin, flexible tube called catheter is put into the blood vessel in the
arm. A iodine rich contrast material dye is inserted into the patients
bloodstream to enhance the area of interest tissue or artery. A medication that
slows or stabilises the patient’s heart rate to improve the imaging results. Patient lies in
CT scanner for about 10 minutes and must hold breath between 10-30 seconds
during imaging (Mendes, 2014).  

The advantages of CT
angiography it has a higher temporal and spatial resolution, which allows the
specialist to see small structures without motion artefact. The more
slices (between 128 and 320 slices) are essential to the very short scan time
(1- 2s). It gives improved
actualisation and visualisation in 3D of the vessels of the heart, nearby
vessels and coronary structure. This has meant the visualisaton of anatomy can
be done in several planes (Scottsdale
Medical Imaging, 2017). The advantages of high resolution technology are
essential to better image quality with the same radiation dose or to the same
image quality with a lower radiation dose. The advantages of higher temporal
resolution are essential to a reduced use of drug administration. CT angiography
can capture vessels from an
unlimited number of angles, from both inside and outside the vessel wall. It detects
arrowing and obstruction of blood vessels which allows for potentially
corrective therapy to be done. Its more precise anatomical detail than magnetic
resonance imaging (MRI) particularly in small blood vessels. With variability of visualise techniques such
as multiplanar reconstructions, volume rendered (VR) images, and maximum
intensity projections (MIP) and vessels walls can be assessed (Larner, 2017).

Multiplanar reformation (MPR) is
technique that presents plane in 3D image volume. This plane may be at right
angles to the axial slices of the image volume. Luminal narrowing of located plaques
can be evaluated by assessing plaques in planes longitudinal and ninety degree
to the vessel midpoint (Voros, 2009).                                                                                                                                                      A
maximum-intensity projection (MIP) each pixel in the image a ray is cast
through the 3D image volume and only the highest-attenuation voxels are kept.
MIP shows coronary arteries plus their side branches in a sole image and can image
smaller branches with less attempt contrast with other 3D techniques. MIP
technique used in complete image volume and the coronary arteries will overlap
with the contrast-medium cardiac hollows, high-attenuation pericardial metal staples
and bones of the rib cage can cover these structures (Crownover and Bepko, 2017).

Additionally, if surgery is required, it can be
carried out more accurately. CT angiography is quick, non-invasive and have
less complications. To perform
a CT it can last up to 20 minutes compared to an MRI scan that can last up to
1.5 hrs. CT angiography is lower cost examination compared to 2/3 investigations
required to make a diagnosis which can help in earlier detection of disease. There
is also potentially less discomfort because contrast material is injected. Minimising
Radiation Exposure Special care is taken during x-ray investigations to use the
lowest radiation dose possible while creating the greatest images for assessment.
Modern x-ray systems have very controlled x-ray beams and dose control methods
to minimise stray (scatter) radiation. This ensures that those parts of a
patient’s body not being imaged receive minimal radiation exposure, including
tailoring the scan parameters specifically to their body type and weight (RSNA, 2017).

On the other hand the disadvantages are, awareness of the
vitalness that there is a radiation dose. But the lifetime attributable risk of cancer
from an effective radiation dose of 10 mSv is small, in the order of 1 in 2000,
but varies with age and gender. MRI does not use radiation to acquire
images, but MRI imaging is extensive procedure and is an expensive diagnostic
scanning tool (Voros, 2009).                                                                                                                                                                                  Thinner
slices improve the quality of the 3-dimensional image; on the downside it also
increases the image noise and radiation dose because of the larger overlap and
lower pitch, which increases achievement time and potentially limit the
diagnostic accuracy of the CTA examination. The CTA images are usually
reconstructed with a medium smooth reconstruction kernel. The reform kernel,
also known as filter which is most vital parameters affecting the image
quality. There is weigh up between the spatial resolution and noise for each
kernel. Smooth kernels produce images with little noise, resulting in lower
spatial resolution. However sharp kernel, produces images with high spatial
resolution but have amplified noise levels (Wong
and Keng, 2011).                                       

A person who is very large may not fit into the opening
of a CT scanner or may be over the weight limit usually 450 lbs for the moving
table. Tube current can be modified according to the patient body mass index
(BMI). Higher tube current increases the amount of photons per exposure time,
reducing the image noise, but at the same time increasing the radiation dose.
Patients with higher BMI need higher tube current to reduce the noise level,
generated by the higher amount of tissue penetrated (Dewey, 2009). The tube current should only be increased to a
level necessary for acquiring adequate diagnostic images. Increasing tube
voltage will lead to higher energy X-ray beams with higher tissue penetration,
and substantially increased radiation dose. Generally, 100 to 120 KeV tube
voltages are sufficient for cardiac imaging. Only in large patients, 140 KeV
could be used. Reducing tube voltage will reduce radiation dose in proportion
to the square of changes in tube voltage (Roberts
et al, 2008).

 

 

 

CTA contra-indications are if patients who are at risk
for kidney failure and who already have borderline kidney function,
administering iodinated contrast material could potentially further damage
kidney function. Large quantity of x-ray contrast material outflows from the
vein being inserted and spreads beneath the skin where the intravenous is located,
it may harm the skin, blood vessels and nerves (Robert et al, 2008). CT
angiography should be avoided in patients with a previous severe reaction to
contrast material, advanced kidney disease or severe diabetes, because x-ray
iodine-rich contrast material may be harmful. Medical history of allergy to
x-ray contrast material, the specialist may instruct them to take special preventive
medicine such as a steroid, for a few hours or the day before of scan to reduce
the risk of allergic reaction. Women always should notify their specialist if
there is any likelihood that they are pregnant. Contrast medium manufactures direct
mothers must not breastfeed their babies after contrast medium is given for about
24-48 hours (Khan et al, 2010).                                                                                                
                                A non-compliant patient, leads to movement
artefact. CTA is unsuitable when there is a large amount of existing coronary
artery calcification. Arrhythmias (irregular heartbeat) and unusually high
heart rates. Artefact (degrade image quality) due to pulsation from blood flow
in vessels and the chambers of the heart, respiratory artefact, beam-hardening
effects caused by implant/metal artefacts or air bubbles in the pulmonary
artery. Patient inability to hold a breath for at least 15-20 secs (Dewey, 2011).