Multislice Computed Tomography Angiography in Pulmonary Embolism Diagnosis - Essay Example

Multi-slice CT Scan Number Department TABLE OF CONTENTS Introduction 3 2. The Multislice Computed Tomographic Pulmonary Angiographic (MSCTPA) 4 3. Review of Literature 5 4. Principle of Imaging 5 5. Pathways of Imaging 7 6. Accuracy of Diagnoses 8 7. Limitations of MSCTPA 10 8. Reduction of Dose Risks 10 9. Conclusion 12 10. References 13 Function of the MSCTA (Multislice Computed Tomography Angiography) in Pulmonary Embolism Diagnosis Introduction Research shows that only stroke and myocardial ischemia cause more cardiovascular fatalities in the world than PE (pulmonary embolism). In a year alone, about 22 to 70 people per 100, 000 acquire this complication, therefore, making it a very prevalent disorder. It is usually treated through anticoagulation, and is quite deadly if not treated. Pulmonary embolism is basically a result of blockage of a branch of any pulmonary artery caused by a thrombus (obstruction) in the venous system. Medical professionals reckon that the condition often leads to arrhythmias, heart malfunctions and/ or varicose veins that usually follow from surgery of the prostate glands thereby enhancing clotting tendencies of blood because malignancy presence. The size of the thrombus, which determines the location of the embolus, in many instances varies from the size of arteries that are sub-segmental to that of a pulmonary trunk. Patients of pulmonary embolism exhibit different thrombus sizes located in various regions (Ller and Emil, 2007, p. 4). Pulmonary embolism is characterised with symptoms common to other ailments along with considerable levels of mortality and morbidity. For instance, symptoms of pulmonary embolism such as pains in the chest and short breaths are also symptoms of diseases of the pleura, gastrointestinal tract, lungs, and so on, thus causing problems during diagnoses. It is consequently a fact that we more patients being evaluated for the condition rather than being diagnosed. The pulmonary arteries are incompletely or totally blocked by acute pulmonary embolism. Morbidity is a huge phenomenon of the disease, even during anticoagulation treatment, meaning that prompt and precise diagnoses of the ailment are quite important (Beek, 2009, p. 8). Originally, ventilation perfusion scintigraphy was the first procedure employed with patients thought to have pulmonary embolism. This method is considered least non-invasive and is faster, permitting diagnosis and/ or exclusion of pulmonary embolism in a considerable population of pulmonary embolism cases. On the other hand, based on the kind of patient and the evaluation methodology used, 40-70% of the results gotten from the procedure are usually non-diagnostic hence more tests are needed because on average, about 25% of these non-diagnostic cases often have pulmonary embolism (Bushong, 2000, p. 256). The contemporary techniques of pulmonary embolism diagnoses entail numerous procedures and are quite cumbersome. Clinicians would therefore strongly embrace and appreciate a single method (test) that offers accurate diagnosis and prognostic data on pulmonary embolism (Cierniak, 2011, p. 345). Computed tomography techniques, and more specifically, the MSCTPA, is the best way for many radiologists. This essay thus discusses MSCPTA and compares and contrasts some literature available concerning the technique and its role in the diagnosis of pulmonary embolism. The Multislice Computed Tomographic Pulmonary Angiography (MSCTPA) Made up of a number of row detectors that are capable of simultaneously gathering information from various body parts, the MSCTPA is a special kind of computer tomography. Because of the capability of these detectors, the MSCTPA enable faster scanning and enhances treatment of PE. Basically, in the procedure, specialised tests are performed to create pictures of the pulmonary arteries after the injection of a material of iodinated contrast (Elliott, 2000, p. 34). Review of Literature In this research, in order to get the latest information on the particular issue, peer-reviewed and scholarly books and articles from the year 2000 to the present day (2015) were used. The peer reviewed journals and articles came from sites such as Science Direct, Oxford Journals, Pubmed, Medline, EBSCOhost, ProQuest and Emerald with the books (equally peer reviewed) coming from searches in the internet. To improve on the search criterion, terms preferably used included phrases such as Multislice Computed Tomography (MSCT), Pulmonary Embolism, and Computed Tomography (CT). Examples of other phrases used in the search included ‘medical imaging importance in pulmonary embolism diagnoses’ and ‘success of MSCTPA in the diagnosis of pulmonary embolism’. An item was picked based on factors such as abstracts, conclusions, titles, and presence of highlighted outcomes of the source’s research there-in. The major topics delved into in the literature review were principles of imaging, pathways of imaging, MSCTPA’s accuracy of diagnosis, limitations of the MSCTPA, and radiation protection during the use of MSCTPA. The sources cited in this article boast high credibility, are authored by qualified persons in the subject of radiology with vital data and knowledge of the use of the MSCTPA in pulmonary embolism diagnosis. Principles of Imaging With even more promise of diagnosis additional ailments like the disease of the coronary artery, computed tomography is presently a useful method of treating cardiovascular conditions like pulmonary embolism and aortic dissections. In contrast with earlier scanners, today’s scanners come with better temporal and spatial resolutions which mean that the reconstruction of images is possible on different planes such as three dimensional ones (Grangeat, 2009, p. 365). A great change has taken place in diagnostic imaging following the inception of the volumetric computed tomography scanning which employs helical or spiral scanners. Several new applications of computed tomography scanning have come to the fore including lung and liver lesions detections, angiography of computed tomography and renal colic. Computed Tomography is the best way of obtaining the patients’ images which occur sequentially and consecutively in slices that are slender therefore offering a way of locating objects in three dimensional planes. This technique has significantly reduced the duration of diagnoses. With a 0.4×0.4×0.4 mm resolution and a 0.5mm collimation, the entire process can be done in less than 10 seconds with a 64 multi scanner (Konstantinides, 2007, p. 400). To make sure that the pulmonary tree gets good opacification of diagnosis, the first step while performing the MSCTPA entails issuing the patient with instructions for breathing so that there is a desirable inspirational breath holding capacity. The next process entails explaining to the patient about the contrast media and highlighting some side effects. The third step involves enhancement of contrast in the pulmonary phase so that there is a superior capture of the image of the pulmonary tree. Next, for improved opacification, the arterial/ pulmonary system ought to be totally covered in the direction of the cephalic-caudal. In the first contrast media flow, the pulmonary tree should be captured in order to evade the venous system’s artifacts. Lastly, information should be gathered through efficient algorithms followed by reconstruction of contiguous sections. This reconstruction can be carried out with an algorithm of 2mm maximum thickness and spatial resolution that is intermediate (Marchal, 2005, p. 469). To achieve useful results, the protocol of scanning must be in tandem with the medical condition. In addition, the computed tomography test ought to be done by an experienced and well trained technologist of computed tomography who is in turn supervised by a physician with extensive know how on the matter. Radiation exposure depends on the protocol of imaging employed. The protocol for the use of the 64 MSCTPA for a patient suspected of pulmonary embolism, for instance, entails a rotation of time of 0.33 seconds using 200mAs and 100kVp. The coverage volume is inversely proportional to the slice thickness where superior resolution is permitted in thinner slices. Intervals of data reconstruction should be 0.5mm, collimation detector at 0.6mm with a thickness of about 0.75mm in cases of suspected pulmonary embolism. In this case, 320mg/ ml visipaque media of about 100-120ml is injected at the average rate of 3ml/s into the IV (Mikla and Victor, 2014, p. 501). Pathways of Imaging In approximately 93% of pulmonary embolism patients, there are no symptoms with only signs of chest pains available (even these are less than 1%). Because the clinical features’ PV is poor, the high rates of mortality in pulmonary embolism cases require that thrombolysis be taken into consideration in inpatient setups. Patients with low to average probabilities of pre-test with positive D-dimers and the ones with pre-test probabilities that are high undergo imaging (Naff, 2006, p. 153). Pre-test probabilities determination is the pioneer procedure in reaching imaging decisions since not every patient exhibiting symptoms of pulmonary embolism should be assumed for imaging. The potential of one being sick with pulmonary embolism is gauged from these pre-tests. Pre-tests/ guidelines for clinical determinations could be Geneva rules or Wells rules. Using the Wells rules, patients are classified as high, intermediate, or low probability. Low molecular weight heparin therapy is recommended when diagnosis of pulmonary embolism fails with the D-dimer while in referrals for imaging are instantly advised for probabilities that are high. The next procedure is the testing of D-dimer. The D-dimer is used here since it has a sensitivity of more than 95% making the ruling out of pulmonary embolism in intermediate and low probabilities more accurate. In the end, the low and intermediate probability people with positive D-dimers and the high probabilities are taken for imaging (Scillia and Gevenois, 2004, p. 295). Accuracy of Diagnosis The discovery of scanning methods of spiral computer tomography has permitted the capturing of pictures of pulmonary artery in single hold of breath and in the process of optimal contrast enhancement. Because of its numerous advantages, this contemporary method of pulmonary embolism diagnosis is the most prevalently used. Physicians find it handy because of its good accuracy in diagnosis, information handling simplicity, chances of obtaining extra data on additional abnormalities of the walls of the chest, mediastinum and lungs, that is, it also offers extra diagnoses. The use of MSCPTA was followed by operations in 38 individuals in a survey designed to ascertain the value of diagnosis of the 64 MSCPTA in the cut off and run off areas of arterial disease patients. The individuals exhibited symptoms and signs associated with arterial disease, with all indicating vascular surgery. A 64 slice scanner was employed and in the step of arterial injection, a non-ionic contrast substance was injected into the antecubital vein with a power injector at the rate of 5ml/ sec. Re-vascularisation of the arterial disease was performed intraoperatively. The results of the MSCPTA showed that the superficial femoral artery was where most of the stenosis took place. A high agreement level in the rates was demonstrated by the Spearman’s coefficient. Compared to surgery the PPV, NPV, specificity, sensitivity and MSCPTA accuracy were 96.7%, 81.2%, 95%, 83.2% and 88% respectively. The surgical figures acted as the reference standard and in most instances showed concordance (81.5%). The MSCPTA thus identified virtually all of the sites that were cut-off, that is, in 97.4% of the individuals. In a second survey using the PIOPED II, the outcomes indicated that the specificity and accuracy of the MSCPTA in diagnosing pulmonary embolism were 97% and 84% respectively. These results simply say that when diagnosis of pulmonary embolism using MSCPTA was performed, a false negative rate of 3% was obtained in the absence of pulmonary embolism where as a false positive rate of 16% was gotten in the presence of pulmonary embolism. When the survey introduced a computed tomography venography, the specificity showed no significant changes while the sensitivity was enhanced further. In the survey, the negative and positive PVs were absent in individuals with high to moderate pulmonary embolism development risks. The date in this second survey came from the use of four row detector computer tomography, therefore, the study is quite old. This was contrasted with the first study which utilised the 64 MSCPTA scanners with greater accuracies, specificity, sensitivity and results in line with the diagnosis of sub segmental pulmonary embolism. Strains of sign in the CTPA’s RV were evident in a third study that sought to determine the capability of the MSCPTA in telling the severity and progress of pulmonary embolism in patients. Compared to the results of the echodiographic employed in dysfunction of RV detection, there was 100% specificity and 79-93% sensitivity (LeVine, 2010, p. 411). Lastly, a recent survey endeavoured to ascertain the strength of a CAD (computer associated detection) algorithm, and contrast the readings of radiology in the absence and presence of the computer associated detection. The survey was made up of diagnosed individuals, 158 of which had no pulmonary embolism while 51 had the disease. The outcome proved that CAD use enhances detection sensitivity in the sub-segmental and segmental pulmonary embolism from 79% to 91% with the specificity remaining constant at 86%. The software therefore improves on the user’s ability to diagnose pulmonary embolism and does not interfere with the superior specificity (Leondes, 2005, p. 418). Limitations of MSCPTA Despite the fact the MSCPTA has numerous advantages and successes in pulmonary embolism exclusions the technique also has its limitations. For one, there are allergic reactions. The media for contrast is excreted from the human body via the renal system and in instances where the patient has some renal issues the contrast media’s toxicity levels could elicit allergic reactions in the patient. Secondly, there is the problem of high radiations level exposure when using MSCTPA. This presents a lot of health risks especially in children and in pregnancy when exposure of the foetus to harmful radiation can result in considerable harm both to the developing child and the mother (Haidekker, 2013, p. 377). Reduction of Dose Risks Since the application of the MSCPTA causes exposure to radiation, as has been noted, longer exposures may have harmful effects. The principle of radiation protection, as enshrined in the Radiation Act, requires that each person should not be subjected to exposures that are unnecessary via substances and waves that are radioactive (Seemann, 2005, p. 330). According to the act, this protection is achieved using processes of optimisation, limitation and justification. Strategies of reducing doses of radiation are available with the use of the MSCPTA with aims of preventing exposures. One of these means is through the regulation of the current in tubes which is made possible through various modifications of the X-ray tube originating current in the entire process of scanning in three (x, y, and z) dimensions. This current modulation, as it is called, minimises the radiation dosage by about 22%. The modification in the X axis minimises doses by up to 26%. Moreover, radiation exposure is minimised using the modulation of the peak kilovoltage. This modulation works by lowering energy of the x ray which in turn lowers the radiation yielded (Seeram, 2009, p. 312). The modification of the length of scanning where the time taken to complete the imaging is reduced means also that it therefore minimises exposure. It is equally thought that modifying the scanning length just beneath the heart from the aorta’s arch keeps the diagnostic accuracy yet lowers radiation dosage by 37%. The Dual Energy Computer Tomography also reduces exposure to radiation as it promotes better contrast by permitting substance decomposition on the chest’s air space, iodine and soft tissues. There are two kinds of Dual Energy Computer Tomography as determined by the configuration of the X-ray tube. These are the single source Dual Energy Computer Tomography and dual source Dual Energy Computer Tomography. Apart from yielding superior quality of CTPA pictures, reducing the volume of contrast media used and enhancing diagnostic accuracy, Dual Energy Computer Tomography considerably lowers radiation doses. The dual DECT however is known to provide higher reductions of radiation doses than its counterpart, the single DECT (Stein, 2007, p. 413). Lastly, there is the iterative re-construction which is less vulnerable to noise in images than the filtered black projection that has been used since time immemorial. The filtered black projection enhances clinical throughput due to its relative simplicity in computation that enables microsecond reconstruction of images. In the past, with the power of the available computers, image reconstruction was not possible with the iterative re-construction and the methods present were quite complex. However, with advancement reconstruction has been achievable with scanners of the MSCT. In the contemporary iterative re-construction, scanning information file is yielded via simulation and checked against the real scanning information measurement. The FBP is produced according to the HU values (calculated attenuation measurements) from the pioneer image. Factors of correction are generated as the image further undergoes iteration to yield an image even more corrected. This can be repeated six times to produce better results. Variation of iterative results in pictures similar to the ones generated by an FBP with similar resolution and minimised noise. This reconstruction method lowers the dose of radiation by close to 25% (Ghersin, 2006, p. 238). Conclusion Pulmonary embolism is hence a very fatal and dangerous disease as has been seen in the sections above. In the past, there have been challenges in the exclusion and diagnosis of pulmonary embolism, but the development of the MSCPTA has facilitated a singular and easier approach. MSCPTA has enhanced treatment of the disease by enabling fast exclusions. Also, in as much as the technique presents a myriad of benefits to health care, it also possesses some limitations such as allergic reactions and radiation exposure. However, there are interventions that have been initiated to curb these limitations, a fact that makes the use of MSCPTA in the diagnosis of pulmonary embolism quite irreplaceable (Blann, 2009, p. 124). References Beek, Edwin J. R. Van. Deep Vein Thrombosis and Pulmonary Embolism. Chichester, UK: J. Wiley-Blackwell, 2009; 78. Blann, Andrew D. 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