Computed tomography angiography: Difference between revisions

{{moreMore citations needed|date=July 2014}}

'''Computed tomography angiography''' (also called '''CT angiography''' or '''CTA''') is a [[computed tomography]] technique used to visualizefor [[arterialangiography]]—the andvisualization of [[venousarteries]] vesselsand throughout[[veins]]—throughout the [[human body]]. Using contrast injected into the blood vessels, images are created to look for blockages, [[aneurysm]]s (dilations of walls), [[Dissection (medical)|dissections]] (tearing of walls), and [[stenosis]] (narrowing of vessel). CTA can be used to visualize the vessels of the heart, the aorta and other large blood vessels, the lungs, the kidneys, the head and neck, and the arms and legs.{{citation needed|date=June 2022}} CTA can also be used to localise arterial or venous bleed of the gastrointestinal system.<ref name="pmid28362508">{{cite journal | vauthors = Wortman JR, Landman W, Fulwadhva UP, Viscomi SG, Sodickson AD | title = CT angiography for acute gastrointestinal bleeding: what the radiologist needs to know | journal = The British Journal of Radiology | volume = 90 | issue = 1075 | pages = 20170076 | date = July 2017 | pmid = 28362508 | pmc = 5594987 | doi = 10.1259/bjr.20170076 }}</ref>

[[Coronary CT angiography]] (CCTA) is the use of CT angiography to assess the [[coronary artery|arteries]] of the [[heart]]. The patient receives an [[intravenous injection]] of [[radiocontrast|contrast]] and then the heart is scanned using a high speed [[CT scanner]]. With the advances in CT technology, patients are typically able to be scanned without needing medicines by simply holding their breath during the scan. CTA is used to assess heart or vessel irregularities, location of stents and whether they are still open, and occasionally to check for atherosclerotic disease.<ref name=":0" /> This method displays the anatomical detail of blood vessels more precisely than [[magnetic resonance imaging]] (MRI) or [[ultrasound]]. Today, many patients can undergo CTA in place of a conventional [[catheter]] [[angiogram]], a minor procedure during which a catheter is passed through the blood vessels all the way to the heart,. howeverHowever, CCTA has not fully replaced this procedure. CCTA is able to detect narrowing of blood vessels in time for corrective therapy to be done. CCTA is a useful way of screening for arterial disease because it is safer, much less time-consuming than catheter angiography, and is also a cost-effective procedure.

CTA can be used in the chest and abdomen to identify [[aneurysm]]s in the aorta or other major blood vessels. These areas of weakened blood vessel walls that bulge out can life-threatening if they rupture. CTA is the test of choice when assessing aneurysm before and after endovascular stenting due to the ability to detect calcium within the wall.<ref name=":1" /> Another positive of CTA in abdominal aortic aneurysm assessment is that it allows for better estimation of blood vessel dilation and can better detect blood clots as compared to standard [[angiography]].<ref name=":2" />

[[CT pulmonary angiogram]] (CTPA) is used to examine the pulmonary arteries in the lungs, most commonly to rule out [[pulmonary embolism]] (PE), a serious but treatable condition. It has become the technique of choice for detection of pulmonary embolism due to its wide availability, short exam time, ability to see other diseases that may present like pulmonary embolisms, and a high degree of confidence in the validity of the test.<ref name=":1">{{Cite book | first1 = Vicky | last1 = Goh | first2 = Andy | last2 = Adam | name-list-formatstyle = vanc |title=Grainger & Allison's diagnostic radiology. |date=2016 |publisher=Elsevier |isbn=9780702069352 |oclc=922460588}}</ref><ref name=":2">{{Cite book|title=Essential Radiology|date=2014|publisher=Georg Thieme Verlag|isbn=9781604065732|editor-last=Gunderman|editor-first=Richard B. | name-list-formatstyle = vanc |location=Stuttgart |doi=10.1055/b-002-92682|s2cid=257312634 }}</ref> In this test, a PE will appear as a dark spot inside the blood vessel or a sudden stop of the bright contrast material.<ref name=":2" />

CT angiography should not be used to evaluate for [[pulmonary embolism]] when other tests indicate that there is a low probability of a person having this condition.<ref name="ACCPandATSfive">{{Citation|author1=American College of Chest Physicians|title=Five Things Physicians and Patients Should Question|date=September 2013|url=http://www.choosingwisely.org/doctor-patient-lists/american-college-of-chest-physicians-and-american-thoracic-society/|work=[[Choosing Wisely]]: an initiative of the [[ABIM Foundation]]|page=|publisher=American College of Chest Physicians and American Thoracic Society|access-date=6 January 2013|author2=American Thoracic Society|author1-link=American College of Chest Physicians|author2-link=American Thoracic Society}}, which cites

* {{cite journal | vauthors = Fesmire FM, Brown MD, Espinosa JA, Shih RD, Silvers SM, Wolf SJ, Decker WW |date=June 2011|title = Critical issues in the evaluation and management of adult patients presenting to the emergency department with suspected pulmonary embolism | journal = Annals of Emergency Medicine | volume = 57 | issue = 6 | pages = 628–652.e75 | date = June 2011 | pmid = 21621092 | doi = 10.1016/j.annemergmed.2011.01.020 |pmid doi-access =21621092 free }}

* {{cite journal |display-authors=6| vauthors = Qaseem A, Snow V, Barry P, Hornbake ER, Rodnick JE, Tobolic T, Ireland B, Segal J, Bass E, Weiss KB, Green L, Owens DK |date display-authors =Jan–Feb 20076 | title = Current diagnosis of venous thromboembolism in primary care: a clinical practice guideline from the American Academy of Family Physicians and the American College of Physicians | journal = Annals of Family Medicine | volume = 5 | issue = 1 | pages = 57–62 | date = Jan–Feb 2007 | pmid = 17261865 | pmc = 1783928 | doi = 10.1370/afm.667|pmc=1783928|pmid=17261865 }}

* {{cite journal |display-authors=6| vauthors = Torbicki A, Perrier A, Konstantinides S, Agnelli G, Galiè N, Pruszczyk P, Bengel F, Brady AJ, Ferreira D, Janssens U, Klepetko W, Mayer E, Remy-Jardin M, Bassand JP |date display-authors =September 20086 | title = Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC) | journal = European Heart Journal | volume = 29 | issue = 18 | pages =2276–315 2276–2315 | date = September 2008 | pmid = 18757870 | doi = 10.1093/eurheartj/ehn310 |pmid doi-access =18757870 free }}</ref> A [[D-dimer]] assay might be a preferred alternative to test for pulmonary embolism, and that test and a low clinical prediction score on the [[Pulmonary embolism#Diagnosis|Wells test]] or [[Geneva score]] can exclude pulmonary embolism as a possibility.<ref name="ACCPandATSfive" />

[[File:CTA FMD.jpg|thumb|436x436px|Volume rendered CTA of renal arteries in patient with medial fibromuscular dysplasia.]]

Visualization of blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure and those suspected of having kidney disorders can be performed using CTA. Stenosis (narrowing) of a renal artery is a cause of [[hypertension]] (high blood pressure) in some patients and can be corrected. A special computerized method of viewing the images makes renal CT angiography a very accurate examination.<ref>{{cite journal | vauthors = Liu PS, Platt JF | title = CT angiography in the abdomen: a pictorial review and update | journal = Abdominal Imaging | volume = 39 | issue = 1 | pages = 196–214 | date = February 2014 | pmid = 24026174 | doi = 10.1007/s00261-013-0035-3 | s2cid = 34899206 }}</ref> CTA is also used in the assessment of native and transplant renal arteries.<ref name=":1" /> While CTA is great for imaging of the kidneys, it lacks the ability to perform procedures at the same time. Thus traditional catheter angiography is used in cases of acute renal hemorrhage or acute arterial obstruction.<ref name=":0" />

=== Carotid, vertebralBrain and intracranialneck vessels ===

[[File:CT angiography of a vascular malformation with intraventricular hemorrhage.png|alt=|thumb|437x437px|CTA of a vascular malformation with intraventricular hemorrhage.]]

CTA can be used assess acute stroke patients by identifying clots in the arteries of the brain.<ref name=":0" /> It can also be used to identify small aneurysms or [[arteriovenous malformation]] inside the brain that can be life-threatening. While CTA can produce high quality images of the [[carotid arteries]] for grading the level of [[stenosis]] (narrowing of the vessel), calcium deposits (calcified plaques) in the area where the vessels split can lead to interference with accurate stenosis grading. Because of this, [[magnetic resonance angiography]] is used more often for this purpose.<ref name=":1"/> Other applications of CTA are identifying [[moyamoya disease]], dissections of intracranial arteries, detection of [[carotid-cavernous fistula]], planning for intracranial-extracranial bypass surgery, and involvement of brain tumours such as [[meningioma]] with surrounding intracranial vessels.<ref>{{Cite book |last1=Hirai |first1=Toshinori |last2=Korogi |first2=Yukunori |last3=Takahashi |first3=Mutsumasa |last4=Yamashita |first4=Yasuyuki |date=2005 |editor-last=Catalano |editor-first=Carlo |editor2-last=Passariello |editor2-first=Roberto |title=CT Angiography in the Assessment of Intracranial Vessels |url=http://link.springer.com/10.1007/3-540-26984-3_5 |language=en |location=Berlin/Heidelberg |publisher=Springer-Verlag |pages=55–67 |doi=10.1007/3-540-26984-3_5 |isbn=978-3-540-40148-3}}</ref>

{{SeeFurther|Contrast CT}}

CT angiography is a [[contrast CT]] where images are taken with a certain delay after injection of [[radiocontrast]] material. The contrast material is [[radiodensity|radiodense]] causing it to light up brightly within the blood vessels of interest. In order for the CT scanner to be able to scan the correct area where the contrast is, the scanner uses either automatic detectors which start scanning when enough contrast is present, or small test boluses. With the small test bolus, a small amount of contrast is injected in order to detect the speed that the contrast will move through the blood vessels. After determining this speed, the full bolus is injected and the scan is begun at the timing determined by the test bolus. After the scan is completed the images are post-processed to better visualize the vessels and can even be created in the 3D images.<ref name=":3">{{cite journal | vauthors = Kumamaru KK, Hoppel BE, Mather RT, Rybicki FJ | title = CT angiography: current technology and clinical use | journal = Radiologic Clinics of North America | volume = 48 | issue = 2 | pages = 213–35, vii | date = March 2010 | pmid = 20609871 | pmc = 2901244 | doi = 10.1016/j.rcl.2010.02.006 }}</ref>

A reaction may occur whenever iodine contrast is injected. These reactions range in severity and it is difficult to predict if they will occur. With the current practice of using low-osmolar contrast these adverse reactions only occur in ~0.1% of cases.<ref name=":2" /> The severity of the reaction can be broken down into three groups:

* Severe - requires immediate treatment: severe [[bronchospasm]], throat swelling, seizure, severe low [[Hypotension|blood pressure]], and/or cardiac arrest.<ref name=":0">{{cite book | firstfirst1 = Michael Y M | last1 = Chen | first2 = Thomas Lee | last2 = Pope | first3 = David J | last3 = Ott | name-list-formatstyle = vanc |title=Basic radiology|date=2011|publisher=McGraw Hill Medical |isbn=9780071766647|edition=2nd|location=New York|oclc=681348027}}</ref><ref name=":6">{{Citecite journal |last vauthors = Maddox|first=Thomas G.|date=2002-10-01TG | title = Adverse Reactionsreactions to Contrastcontrast Material.material: Recognitionrecognition, Preventionprevention, and Treatment|url=https://www.aafp.org/afp/2002/1001/p1229.htmltreatment | journal = American Family Physician | volume = 66 | issue = 7 | pages =1229–34 1229–1234 |issn date =0002-838X October 2002 | pmid = 12387435 | url = https://www.aafp.org/afp/2002/1001/p1229.html }}</ref>

Contrary to popular belief there is no correlation between seafood allergies and reactions to iodine contrast, as shown by many recent studies.<ref>{{Citecite journal |last vauthors = Westermann-Clark|first=Emma|last2= E, Pepper|first2=Amber AN, Talreja N.|last3=Talreja|first3=Neetu|last4=, Lockey|first4=Richard F.RF |date=April 2015|title = Debunking myths about "allergy" to radiocontrast media in an academic institution | journal = Postgraduate Medicine | volume = 127 | issue = 3 | pages = 295–300 | date = April 2015 | pmid = 25740573 | doi = 10.1080/00325481.2015.1012918 |issn s2cid =1941-9260|pmid=25740573 26420916 }}</ref><ref>{{Citecite journal |last vauthors = Schabelman|first=Esteban|last2= E, Witting|first2=Michael|date=November 2010M | title = The relationship of radiocontrast, iodine, and seafood allergies: a medical myth exposed | journal = The Journal of Emergency Medicine | volume = 39 | issue = 5 | pages = 701–707 | date = November 2010 | pmid = 20045605 | doi = 10.1016/j.jemermed.2009.10.014|issn=0736-4679|pmid=20045605 }}</ref>

Historically it has been thought that contrast material can lead to [[contrast-induced nephropathy]] (also called CIN) in any patient. However, recent studies have shown that the risk of kidney injury caused by [[contrast agent]] in patients with no history of kidney problems occurs extremely infrequently.<ref>{{Citecite journal |last vauthors = Heller M, Krieger P, Finefrock D, Nguyen T, Akhtar S |first=Saadia|last2=Nguyen|first2=Thomas|last3=Finefrock|first3=Douglas|last4=Krieger|first4=Paul|last5=Heller|first5=Michael|date=2016| title = Contrast CT Scans in the Emergency Department Do Not Increase Risk of Adverse Renal Outcomes | journal = The Western Journal of Emergency Medicine: Integrating| Emergencyvolume Care= with17 Population| Health|volume=17|issue = 4 | pages = 404–408 | date = July 2016 | pmid = 27429690 | pmc = 4944796 | doi = 10.5811/westjem.2016.4.28994|issn=1936-900X|pmc=4944796|pmid=27429690 }}</ref><ref name=":4" /><ref name=":5" />

The use of CTA in patientspeople with renal[[kidney failure]], kidney disease or long-standing severe diabetes should be weighed carefully as the use of IV iodine contrast material may further harm kidney function. The decision not to use contrast agents must be weighed against the possibility of misdiagnoses if contrast is not used.<ref name=":4">{{cite journal | vauthors = Luk L, Steinman J, Newhouse JH | title = Intravenous Contrast-Induced Nephropathy-The Rise and Fall of a Threatening Idea | journal = Advances in Chronic Kidney Disease | volume = 24 | issue = 3 | pages = 169–175 | date = May 2017 | pmid = 28501080 | doi = 10.1053/j.ackd.2017.03.001 }}</ref><ref name=":5">{{cite journal | vauthors = Do C | title = Intravenous Contrast: Friend or Foe? A Review on Contrast-Induced Nephropathy | journal = Advances in Chronic Kidney Disease | volume = 24 | issue = 3 | pages = 147–149 | date = May 2017 | pmid = 28501076 | doi = 10.1053/j.ackd.2017.03.003 }}</ref>

Compared with other imaging modalities, CTA is associated with a significant dose of ionizing radiation. DependingVarying onsignificantly with patient age, sex, and exam protocol, CTAradiation mayrisk causemodels apredict considerablecoronary increaseCTA into increase lifetime cancer risk.<ref>{{cite journal | vauthors = Einstein AJ, Henzlova MJ, Rajagopalan S | title = Estimating risk of cancer associated with radiation exposure from 64-slice computed tomography coronary angiography | journal = JAMA | volume = 298 | issue = 3 | pages = 317–23317–323 | date = July 2007 | pmid = 17635892 | doi = 10.1001/jama.298.3.317 | doi-access = free }}</ref> However, there are many clinical situations for which the benefits of performing the procedure outweigh this risk.

By 1994 CT angiography began to replace conventional angiography in diagnosing and characterizing most cardiovascular abnormalities.<ref name="Leipsic">{{cite journal | vauthors = Rubin GD, Leipsic J, Joseph Schoepf U, Fleischmann D, Napel S | title = CT angiography after 20 years: a transformation in cardiovascular disease characterization continues to advance | journal = Radiology | volume = 271 | issue = 3 | pages = 633–52633–652 | date = June 2014 | pmid = 24848958 | pmc = 4669887 | doi = 10.1148/radiol.14132232 }}</ref> Prior to this, conventional angiography had been in use for 70 years.<ref name="Leipsic"/>