Assessment item 3 CT Protocols 2016 Student ID: 11551393 Joshua Shehata CSU Wagga Wagga I, Joshua Shehata, Student ID: 11551393 acknowledge that this is my own work and that I have referenced the information in the assessment to the best of my knowledge. Introduction: Patients are diagnosed everyday with a vast amount of pathologies. In the Medical Practice, there are several amounts of Imaging Modalities to assist with confirming and assessing suspected pathologies. One of these Imaging Modalities is Computed Tomography, the concept of using X-ray scanners and other certain types of equipment to visualise the region of interest and find these pathologies. Non-Contrast Brain CT Scan: (Rhode Island Hospital Patient Services and Information) •Patient Preparation The standard patient preparation is used as with any other imaging modality, assuring that the details of the patient are correct as well as the correct examination being given. They must also have no chance of being pregnant at that time if they happen to be female. Of course, the patient must remove all non-medical artefacts that can be removed. The process should be thoroughly explained to the patient so that they have full knowledge and are comfortable with the examination. • Indications relative to region of interest scanned. Indications of this Protocol include CVA, intracranial bleed, mental status change and Trauma. CVA stands for Cerebrovascular Accident, more commonly known as a stroke. There are various types of stroke, but vaguely the one thing all strokes have in common despite their causes is the blockage or rupture of a blood vessel that disrupts the blood flow to the brain. (Healthline, 2013). Intracranial bleeding is related to the CVA as it is a type of internal bleeding that occurs within the brain. (Cleveland Clinic, 2013). In terms of Mental Status change and trauma, there are various types of pathologies related to this and it may be for the main reason that not enough blood is going to parts of the brain due to the blockage of a vessel that has caused excessive internal bleeding. All of these indications are specific to the reason for performing a non-contrast Brain CT and are hence viable for the scan being performed. Despite this, there are several other Indications for a Non-contrast Brain CT such as acute stroke, closed head injury. (American Academy of Family Physicians, 2013) • Discussion as to the relevance to the discussed protocol. The protocol helps the Diagnosing practitioner examine the patient thoroughly as well as help define the patient’s suspected pathology. This is via the accumulation of compromise of the ALARA principle by minimising the dose as much as possible, as well as providing the patient with an optimum amount of radiation for clear views and minimal noise in the image. This is possible via the various factors throughout the Protocol such as the positioning of the patient, the contrast used, the reformation techniques used as well as the direction of the Topogram. All of which are located on the protocol to help guide the Practitioner to diagnose the patient’s pathology. In terms of the contrast used; the type of contrast, amount of contrast and implementation of the contrast all play a big role. • Contraindications for the selected scan type. There are several Contraindications for Non-contrast CT scans of any region of the body. One of which include the factor of weight in Patients due to how narrow the table is as well as the limited weight that the Scanning table can handle. Another significant factor is the concept of Claustrophobia. Claustrophobia is defined as the “fear of enclosed places” (Better Health Channel, 2016). This may also be a significant factor as it may result in inaccurate scans due to movement of the patient during the scan. Artefacts are also minor contraindications. These can be simple as hair clips, dentures, glasses or anything metal. In each of these cases, all contraindications are applicable to doing non-contrast CT scans of the brain as well due to the inability to accurately scan the Brain well. • Positioning and patient alignment ¬¬ The protocol mentions for the patient to be positioned head/feet first supine. The head should be in the head holder whenever possible to avoid movement of the head during the scan for accurate scan results. The External Auditory meatus (EAM) level should be at the centre of the gantry. To minimise the amount of exposure to the lens of the eyes, the angle at which the scan is taken at should be parallel to a line created by the supraorbital ridge and the posterior margin of the foramen magnum. This is possible through the modification of moving the chin of the patient towards the chest as if it was tucked or by tilting the gantry 15-20 degrees. (Slideshare, 2014). Also, the OMBL (Orbitomeatal Baseline) should be perpendicular to the floor to ensure no rotation of the neck. In some cases, doing either may not be possible however it is considered good practice to atleast try to or successfully perform either one or both of these techniques when achievable. In this case, the standard position of Head first or feet first-Supine is used as well as 1cm superior to the skull vertex. Ideally however, time is saved via Head First because the bed movement is slow and Claustrophobic patients are more comfortable with this because most of their body is not in the bore. This protocol also signifies that the topogram direction is Craniocaudal and hence the head will be entering the bore first as the direction is from the Cranial to the Caudal part of the body. • Contrast requirements, oral, IV and other (where required) In the case given, no requirements are given due to no contrast being given. This is because it is a Non-contrast CT sc¬¬¬an. • Exposure factors (and factors effecting exposure selection) The exposure factors set for this CT scan are 120 kVp, 320 mAs and 1 second of rotation time. In relation to X-ray outputs, it can be seen that the X-ray output is very dependent on the mAs value as it is proportional to it. By increasing the mAs, the X-ray potential is also increased. Hence, it can be deduced that by also increasing the kVp, the X-ray output may also increase. Despite this though, there are some benefits for using higher kVp factors, such as the improvement of Contrast to Noise Ratio for muscle as well as improve the Contrast to Noise Ratio when implementing Iodine. In addition to this, the tweaking of mAs will allow the operator of the CT unit to variate the amount of mottle that will be seen on the CT image produced. In contrast to this, modification of the X-ray tube potential will affect the overall CNR value and hence change the amount of mottle possible on the CT image. (Radiology, 2000). • Pitch (MSCT) Multislice CT Pitch is defined as the distance travelled in millimetres in one 360 degree gantry rotation of the table divided by the total thickness of all the slices acquired. (Radiopaedia, 2007) The use of pitch in multislice spiral CT is different to single-slice spiral CT such that the image quality decreases as the pitch increases in single-slice spiral CT, while in Multislice spiral CT, the sensitivity of raw data interpolation increases in an alternating way as the pitch increase, hence the image quality does not decrease monotonically as it does in Single Slice. The relationship between pitch and sensitivity plots for any set of parameters of Multislice spiral CT assists in finding the most favourable pitch. (NCBI, 1999). Pitches can also have various values. If the pitch value is 1, then the X-ray beams from adjacent rotations were essentially bordering each other. Pitches of greater than 1 implied that there were gaps between the X-ray beams from adjacent rotations. Pitches that were less than 1 implied overlapping of X-ray beams from adjacent rotations and hence double irradiation of some tissue. Therefore, were not clinically used. (Journal of Nuclear Medicine, 2006) • Slice thickness and slice interval. The thinner and finer the slice is, the more detail is given. Thicker slices can also be reformatted to increase the definition for the amount of White and Grey Matter of the brain shown. Slices are taken at more intervals to create thinner slices in the case where images with higher spatial resolution are requested, however this also results in noise levels of a higher acquisition which potentially requires a higher current or tube potential to be used. Despite thicker slices having lower spatial resolution, they also have lower noise levels, which allows more potential for the use of a lower potential of the tube or current. For obvious or common clinical indications, it is recommended that Imagers use the maximum reconstructed slice thickness available to provide enough data for the required information to be given and clinical indication to be detected easily. This is because the overall tube output can be reduced and the radiation can be minimised as much as possible. (Medscape, 2012) • Scan range The Scan Range involves the amount of dose given to and size of the area of interest of the CT scan. When the area of interest involves scans through the orbital region of the Skull, there should be definite attempts to minimise radiation dose to the lens as much as possible. The Scan Range is determined by where the locations of the Scan start and end. In this case, the skull base is the start and the skull vertex is the end. • SFOV The Scan Field of view is defined as the actual area of interest that is selected before the scan begin. Similarly, it is also the region of interest that is scanned by the CT scanner. The Scan Field of View is a determination of how many detectors are required to acquire the data for the scan. The Scan Field of View always has to be larger than the region of interest. This is due to the fact that if it is smaller, the detectors will not record the scan box. This results in artefacts on the scan which results in an inaccurate or invalid CT scan and may result in the false detection of a pathology. (Radiology 101 – Learning the basics, 2016) • Contrast specifications In this case no contrast is used however Contrast Media is still used regularly in examinations such as CTA (Computed Tomography Angiography). There are several types of contrast media used in CT examinations, the specific contrast for Brain CTA will be discussed in the Second Protocol. • Reformation requirements Reformation works such that a volume of data is sliced into slices based on the amount of detail that there is wanted from the data. The thinner the slice is, the more detail is given. Based on the collaboration of slices that you want to be seen, the more or less detail will be seen. For example if the Slice thickness over Interval thickness is 2/1 then 200% of the original data will be covered, however if the ratio is 3/5 in contrast to 2/1, then 60% of the original data is covered. Despite this less coverage of original data, you can see more specificity due to the smaller size of the slice. Thicker slices can be reformatted to increase the definition for the white and grey matter of the brain “Addition of the dimension of depth provides a view heretofore not obtainable by standard imaging techniques and allows more accurate diagnosis as well as a more specific approach to surgical planning and follow-up.” (American Journal of Neuroradiology, 1986) There are several window widths and levels for reporting different studies on a CT. The concept of using windows is the process of transforming Hounsfield Units into specific values that can be used for gray scale. This process of “windowing” helps allow different features of the specified region to be seen. There are two factors to Windowing: Window width (WW) and Window level (WL). Requirements for Reformation include specific ranges of Hounsfield Units to see specific things. For example tissues that consist of Hounsfield Units that exceed the half the sum of the Window level and Window width or the difference of half of the window length and width are set to be all white or all black. When discussing in relation to specifically head CT, Bone Window and Brain Window are very significant. Bone Window as the name suggests is commonly used for the visualisation of bone structures and identify hard to find lesions in the skull. (AMIA, 2012) In this non-contrast Brain CT, there are many Indications for the suspected pathology and hence there are a vast amount of possibilities in terms of what to look for on the CT. A Bone Window may be suggested for significant use of finding easy to find pathologies or even possibly using a Brain Window for more specific pathologies. Computed Tomography Angiography (Rhode Island Hospital Patient Services and Information) •Patient preparation Patient preparation is the standard as that of a Non-Contrast Brain CT scan as mentioned earlier, such as explaining the process to the patient and ensuring the patient details are correct with the procedure being performed; however the performance of the functionality of the renal system must be assessed prior to the examination due to the injection of Intravenous Contrast Media (IVCM). In this case, the patient must have been able to be fasting for a minimum of 4-6 hours prior to the examination. The reason for fasting is so that the contrast is not infused with whatever they consume and hence the chances of Nausea or side effects are reduced. •Indications relative to region of interest scanned. Indications of the given Carotid and Brain CTA Protocol include Carotid/Cerebral Artery stenosis or aneurysm; non-trauma. Carotid stenosis is when the carotid arteries are narrowed. This narrowing is usually caused by plaque which is the build up of cholesterol and fatty deposits. (WebMD, 2005) An aneurysm similarly is when a weak area of the artery wall that is responsible for the bloody supply of the brain begins to bulge. In some cases, the aneurysm potentially ruptures and causes blood to be released into the skull, eventually causing a stroke. (WebMD, 2005). Each of these indications are all requiring Brain CTA for further diagnosis. These indications are specific for this protocol however there are several other CTA indications such as Dural Arteriovenous Fistula, Brain Arteriovenous Malformation, Acute stroke, Suspected Cerebral Vasculitis or even atherosclerotic disease. Other less common indications include Cerebral Activation testing, venous thrombosis, vessel dissection and others which are specifically discussed with the patient prior to the Angiogram examination. (NYU School of Medicine, 2016) • Discussion as to the relevance to the discussed protocol. The protocol helps the Diagnosing practitioner examine the patient thoroughly as well as help define the patient’s suspected pathology. This is via the accumulation of compromise of the ALARA principle by minimising the dose as much as possible, as well as providing the patient with an optimum amount of radiation for clear views and minimal noise in the image. This is possible via the various factors throughout the Protocol such as the positioning of the patient, the contrast used, the reformation techniques used as well as the direction of the Topogram. All of which are located on the protocol to help guide the Practitioner to diagnose the patient’s pathology. In terms of the contrast used; the type of contrast, amount and implementation of the contrast all play a big role. • Contraindications for the selected scan type. Contraindications for CTA include very high sensitivity to Iodinated Contrast agents, History of Allergies or Allergic reactions to other Medications, Congestive heart failure, Multiple Myeloma, Atrial fibrillation, History of thromboembolic disorders, Renal insufficiency, Pheochromocytoma and Inability to hold breath for 15 seconds. Each of these contraindications exist such that they affect the quality of the Diagnostic Image. (The Journal of Nuclear Medicine, 2006). Other related contraindications are the same of that for Non-Contrast CT Brain Scans as stated earlier, including Artefacts, Claustrophobia and Overweight patients. • Contrast requirements, oral, IV and other (where required) Contrast Media allows improvement of the radiologist to see images of inside of the body more clearly and hence may help more easily identify hidden pathologies. There are several types of contrast and in this case, Intravenous. (Johns Hopkins Medicine, 2016) The term Intravenous refers to the entrance of contrast being injected into the veins of the body using a small needle. Intravenous Contrast is used to help outline blood vessels and enhance the detail of the structure of tissue of various organs within the body. In this case, the tissue structure of the brain is highlighted. The contrast that is injected intravenously is very transparent and has a consistency similar to that of water. Being packed into small vials, it is drawn out by a sterile syringe to administer the contrast. The amount of contrast that is used is dependent on various factor’s such as the patient’s medical condition, wellbeing, weight, age and cardiovascular health. (Johns Hopkins Medicine, 2016) In this CTA, the Contrast Volume is 80cc of Omnipaque 350 contrast given at 4cc/sec. This drug is inserted intravenously into the patient’s body for contrast enhancement of images used in Computed Tomography for Head and Body imaging. The Generic name for Omnipaque 350 Contrast is Iohexol and comes in 755mg concentrations. This is the equivalent of 350mg of organic iodine. (Haymarket Media Inc, 2016) In any examination involving the administration of contrast media, risk factors always include whether or not the patient has diabetes, previous history of reactions to administration of the contrast, renal impairment or age. All of which are indicated on the medical imaging request form, however in this case, there seems to be no evidence of any of that. (Queensland Government, 2013). ¬ In relation to the side effects of the contrast agents used, the most common side effects of Iodine include a “flushed” sensation to the patient during the injection as well as the remains of a “Metallic taste” in the mouth. A mild reaction includes the irritation of various parts of the skin which may lead to itching. This side effect usually lasts between a couple of minutes to several hours and there are medications that can be administered by the radiologist, nurse, technologist of various physicians that reduce this side effect. Some of the more serious reactions include shortness of breath, difficulty breathing as well as the body swelling up in various areas such as the throat. (Johns Hopkins Medicine, 2016) Risks of allergic reactions have been significantly reduced with the introduction of the change of the Chemical Structure of the Iodine contrast to make non-ionic contrast. (Imaginis, 2016) • Exposure factors (and factors effecting exposure selection) There are various Exposure factors in Computed Tomography Angiography Protocols including the Kvp given, the mA, the rotation time (seconds), the pitch, the speed and the Standard Deviation. The use of inappropriate exposure factors, as well as the increase of scan volume within the CT procedures results in an increased dose in the patient as well as repeats of CT examinations due to the overlapping of scans in advanced CT machines. This is incorrect as CTA imaging should always reduce dose as much as possible. (Saudi Journal of Biological Sciences, 2016) In this case the CTA has exposure factors of 120 kVp, Sure Exposure of 100-450, .75 seconds, .688:1 pitch, 5.5mm speed and Standard Deviation of 6.9. The rotation time and helical pitch determine the table speed and hence the speed at which the volume is scanned. (AMIA, 2012) Similarly, factors such as Rotation time of the gantry do result in higher or lower doses. However, despite the dose being decreased when the Gantry rotation time is increased, more noise is accumulated. The same applies for the increase in noise when the tube current is decreased as well. Simultaneously, when the kVp is increased despite all the other factors being kept constant, the dose also increases. (Medscape, 2008) This protocol uses both Axial and Helical Scans. Axial for the non-contrast Brain CT scan as stated in the first protocol and Helical for the Brain CTA. There are certain advantages for axial scans and Helical Scans. One of which are the more likely chance to get artefacts in scanners that have below 16 Detector rows. However the amount of artefacts are about equivalent to each other in scanners for the equivalent or more than 64 detector rows. In relation to image quality both have very similar characteristics in cases for scanners that have less than 16 detector rows however in some cases Axial Scans still perform better. Helical Scanners are more modern than Axial Scanners and hence the performance may be better in some cases. (AAPM, 2016) • Pitch (MSCT) Once again, Multislice CT Pitch is defined as the amount of distance in one full rotation of the gantry of the table which is then divided by the thickness of all the slices acquired combined. (Radiopaedia, 2007) In this case the pitch was .688:1. When the pitch is increased, the width of the reconstructed image is increased as well. This is because the projection data from the Z-axis locations are spread further apart. As mentioned earlier, pitch in multislice spiral CT can be contrasted to single-slice spiral CT. One of the ways in which they differ is the connection between the decrease of image quality in single-spiral CT in contrast to Multi-slice spiral CT. This is due to the way that the sensitivity of raw data interpolation is changed alternatively as the pitch increases. Therefore the way that the Image quality decreases is not monotonically as in Single Slice-CT. Patterns between sensitivity and Pitch plots most often provide the most optimum pitch possible for the parameters given by Multislice spiral CT. (NCBI, 1999) As mentioned in the non-contrast Brain CT Scan, Pitches that are less than 1 imply overlapping of X-ray beams from rotations that are adjacent to each other, and hence results in double the irradiation of some of the tissue. In this case, the Pitch is .688:1, which is less than 1. This means that this will result in double irradiation. Hence, this is not clinically beneficial and is not used, modification will be required. (Journal of Nuclear Medicine Technology, 2008) • Slice thickness and slice interval. In this case the slice thickness is 1mm and the slice interval is 0.8mm. As stated earlier, once again the thinner the slice, the more detail is visible. It is also good to keep in mind, that if collimation settings are set to assist in taking thinner slices, most of the time the dose efficiency is reduced (AAPM, 2010). In relation to this, that is to say that when the thickness of a slice is decreased, the dose has to be increased so that the level of noise is maintained just like thicker slices. This is usually caused by an increase in mAs. (International Atomic Energy Agency, 2013). Despite the image quality being increased overall, once again, it is still recommended that Imagers use the maximum reconstructed slice thickness available to provide enough data for the required information to be given and clinical indication to be detected easily. (Medscape, 2012) This is mainly due to the compromise that must be met for the ALARA (As low as reasonably achievable) principle. • Scan range The Scan range is the equivalent of that as the Non-contrast Brain CT Scan and the Topogram direction is also the same, however the scan type is Axial and Helical in contrast to the Axial only scan in the non-contrast Brain CT Scan. As stated before, attempts to minimise the Scan range should be made to minimise dose as much as possible as well as to reduce radiation areas such as the lenses of the eyes. In this case the scan range is 1cm superior to the skull vertex. • SFOV The Scan range is inferior from the back of the skull to the Vertex of Skull. SFOV is the same as that of non-contrast CT as stated earlier in the assessment. • Contrast specifics In this CT Scan, the IV Contrast is once again Omnipaque 350 contrast given at 4cc/sec. Risk factors for the drug include diabetes, previous history of reactions to administration of the contrast, renal impairment or age. All of which are indicated on the medical imaging request form, however in this case, there seems to be no evidence of any of that. (Queensland Government, 2013) • Positioning and patient alignment As mentioned earlier, the ALARA principle should be considered such that exposure to the lens of the eyes should be minimised, via angling the scan to be parallel to the connection of the imaginary line between the posterior margin of the foramen magnum and supraorbital ridge. Key concepts such as the where the EAM level should be as well as the positioning of the Orbitomeatal Baseline. Tilting the gantry is also essential in reducing the amount of exposure. It is always good to at least try to do either to minimise as much amount of exposure to the lens as possible. Each of these principles are also essential as for Non-Contrast CT Brain. Once again, the protocol has signified that the Topogram direction is Craniocaudal and hence the patient will be entering from the Cranial to Caudal region. • Reformation requirements As stated in the previous CT Protocol, there are several types of Windows used for different uses to see various levels of detail of a patient’s specified region. Similarly, Brain Windows are more frequently used for soft tissues of lower densities that cannot be seen by the Bone Window in good detail and hence majority of the abnormalities that are in the brain are found via using the Brain Window. Despite the excellent detail of fine structures such as vasculatures, interfluid spaces and air-filled structures, large bone fractures are better seen in the Brain window setting due to the fact that the Brain Window cannot differentiate as well as the Bone Window when it comes to the subtle details of calcified or bone structures. (AMIA, 2012) In this case, bony and calcified structures are not required to be seen because the Indications for the protocol are more fine and specific to pathologies such as Carotid/ Cerebral Artery stenosis or Aneurysm. Hence, due to this, the Brain Window is more likely to be used to find these finer structures within the CTA. Conclusion: In conclusion, I have found critiquing and researching information about both these articles very beneficial for my future understanding in the field of Computed Tomography. References AAPM. (2010). PowerPoint Presentation. Retrieved May 9, 2016, from https://www.aapm.org/meetings/2010CTS/documents/0930_McNitt-Gray_Teaching_Cases_1_04-29-2010.pdf) AAPM. (2016). Adult Routine Head CT Protocols Version 2.0. Retrieved from https://www.aapm.org/pubs/CTProtocols/documents/AdultRoutineHeadCT.pdf Alkhorayef, M., Babikir, E., Alrushoud, A., Al-Mohammed, H., & Sulieman, A. (2016). 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