Radiol Oncol 2000; 34(2): 137-13.
review
Computed tomographic angiography of body vasculature
Tomaž Kunst, Pavle Berden
Clinical Radiology Institute, University Medical Centre, Ljubljana, Slovenia
Background. The introduction of helical CT scanners in combination with simultaneous opacification of vessels with contrast medium allows the demonstration of vessels within the chosen volume of interest. This examination is called CT angiography. Being a minimally invasive method, it has been quickly acctept-ed in the spectrum of vessel-imaging modalities, as far example: Doppler ultrasound, magnetic resonance angiography, transesophageal ultrasound etc. In the field of cardiovascular radiology, it has been used to demonstrate pathology ofascending and descending aorta, like the aneurysms, dissection, traumatic rupture ar congenital anomalies. It is also very useful in pre-and postoperative follow - up in the aortic stent-graft insertion, a method which has recently become popular. Also the CT angiography has greatly influenced the preoperative calculations and has clearly demonstrated the postoperative anatomical changes as well as complications (i.e. peristental leakage).
Conclusions. In this context, it is comparable to intraarterial angiography and even offers some advantages over the latter. The only draw-back being somewhat lower spatial resolution and longer processing time, but with the advent of a new, so called multi-slice scanners and powerful workstations, these draw-backs will be minimized.
Key words: tomography scanners, X-ray computed; aortic disease - ultrasonography - radiography
Introduction
The advent of spiral (helical) CT has made a great revolution at the performance of body CT and has enabled the development of CT angiography (CTA). It is minimally invasive investigation method of vascular system and
Received 15 May 2000 Accepted 30 May 2000
Correspondence to: Tomaž Kunst, M.D., Clinical Radiology Institute, University Medical Centre Ljubljana, Zaloška 7, SI1525 Ljubljana, Slovenia. Phone: +386 1 131 31 23 (38-34); Fax: +386 1 133 31 044
can in many cases replace a conventional angiography. In CTA, there is a volume of data obtained rapidly with virtually no respiratory misregistration at peak vascular opacification following peripheral injection of contrast. The appropriate timing ensures that either venous or arterial tree is perceived and multiple overlapping slices can be obtained in order to generate two- and three-dimensional reconstructions with no increase in radiation dose to the patient. When performed as a dedicated study, CTA is faster, less invasive and (should be) cheaper than conventional angiography, with a reduced radiation dose.
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However, there is no significant contrast saving and spatial resolution is somewhat limited to the vessel diameter of 1-2 mm.
The technique must be meticulous if good-quality angiograms are to be obtained. The variables that can be altered are collimation ("beam width"), table speed, contrast volume and flow rate and reconstruction index, which are all set according to the volume of interest and suspected diagnosis. From this data, two - and three dimensional images can be generated, like multi-planar reconstructions (MPR), maximum-intensity projections (MIP), shaded surface display (SSD) and volume rendering tecnique (VRT).
Main indications for CTA of aorta and its branches are aneurysms and dissections of thoracic aorta, suspected blunt trauma or thoracic rupture; pulmonary embolism; in abdominal aorta, the diagnosis of aneurysms, dissections, rupture, and suspected pathology in renal or visceral arteries as well as pelvi-cal arteries. It is very useful to perform CTA at first and afterwards surgical or interven-tional procedures on aorta and its branches.
Thoracic aorta
Conventional CT has an established role in detection of aortic aneurysms and dissections. CTA has the advantage of thinner colli-mation and of more axial slices obtained during the peak vessel opacification.1 Entire aorta can be imaged on a single spiral and excellent multiplanar reformats can also be obtained. It can actually demonstrate the size, the extent and the quality of the wall of aneurysm as well as the thickness of intimal flap in the case of dissection (Figurel). True and false lumen can be identified and followed, so the origin of the vessels from true or false lumen or the extension of the dissection into the branches can be determined accurately. Some authors prefer the use of CTA over conventional CT and catheter aor-tography in cases of blunt chest trauma or
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Figure la. A dissection of descendent aorta with intimai flap (arrows) are seen in "left anterior oblique" projection.
Figure lb. The same patient with "right posterior oblique" view.
suspected aortic rupture, although the rate of technically suboptimal results may limit its usefulness.2 Also, the determination and differential diagnosis of congenital anomalies is made (Figure 2). In our institution, we found CTA of a great benefit in preoperative treatment planning and postoperative follow-up at
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Figure 2a. A CT scan showing a right-sided aortic arch and intratracheal left subclavian artery with a diverticulum at the orrifice.
the percutaneously or sugically inserted aortic endoprostheses (Figure 3).
Complex anatomy and the extent and the course of intimal flap can be determined by multiplanar reformats (MPR) or SSD and VRT, respectively.3'4 In order to cover the entire thoracic aorta, it is used a collimation of 3mm, table speed of 4,5 mm/s (pitch 1,5), the volume of contrast is set to 140 ml with the infusion rate of 3 ml/s. In cases when the entire aorta is to be imaged it is used a 5mm
Figure 3a. An aneurysm of descending aorta (arrow) due to a kink of aortic endoprosthesis (arrowhead).
Figure 3b. Reduction of the aneurysm after the insertion of additional endoprosthesis.
collimator with a pitch of 1,5-2. If renal arteries are to be assessed precisely, two spirals are made, one for thoracic and the other for abdominal aorta.
Pulmonary circulation
With CTA it is possible to identify reliably the emboli in central and segmental arteries, but not in the vessels below the fourth division (subsegmental arteries) (Figure 4).5 Therefore,
Figure 2b. Three-dimensional reconstruction showing a right aortic arch with mirror imaging of aortic branches.
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Kunst Tet al. / Computed tomographic nngiography of body vasculature
Figure 4a. Pulmonary arteries without filling defects (arrows).
Figure 4b. Emboli in main pulmonarty arteries (arrows). Lung consolidation in the right lobe (arrowheads), indicating possible infarction.
we scan the patient from the top of aortic arch down to the domes of diaphragm. Ideally, it is used a 3 mm slice with a pitch of 1,5, allowing the scanning time of 20 - 25 sec., but patients usually cannot hold the respiration so long, so
we have to use the 5 mm slice and the pitch of 1-1,5, so that the scan duration of about 10 seconds is achieved.
Reported sensitivity and specificity for the detection of pulmonary emboli are 87 and 95%, in comparison with V/Q scans where the result is 65 and 94 %. Therefore, many authors advise new protocols for highly suspicious PE: Doppler US of the lower limbs and CTA of pulmonary arteries, which not only reliably determines emboli, but enables a very accurate differential diagnosis.6'7 Scintigraphy and pulmonary angiography should be reserved for negative CTA with possible subsegmental emboli.8 CTA can also be used for follow-up, i.e. to determine the effectiveness of the treatment.9
Abdominal aortoiliac disease
Conventional CT with contrast was frequently used for the assessment of abdominal aortic aneurysms and provided accurate information about the size of the aneurysm, thrombus formation and diameter of true lumen.10;n CTA can provide all this information, as well as can accurately assess the concomitant renal or mesenteric artery stenoses (Figure 5). It also provides useful information for abdomino-iliacal stent-graft insertion, like the necessary device length and diameter, distance of the neck of aneurysm to renal arteries, and the involvement of pelvic arteries. 12,13 After the insertion, it is used to confirm the success of the procedure, and for detection of the complications, like kicking of the stent and peri-stent leaks.14
Although there exist many different protocols for performing abdominal and pelvic CTA, we are using the following method: after having made native scans, the collima-tion is set to 5 mm and table speed at 7,5 mm/s, enabling the scan from above the coeli-ac trunk or superior mesenteric artery down to external iliac artery in a single scan. Axial reconstruction is made at 3 mm interval, and
Figure 4c. Multiplanar reconstruction of left pulmonary artery, demonstrating a massive thrombus (arrows).
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cation and contrast-filled lumen, and SSD for the morphological assessment. MPRs are made for the measurements, and after the therapeutical procedures, the same imaging protocol is used for comparison.
Other indications
CTA has proven to be superior to conventional CT in the cases of preoperative assessment of live renal donors19-20, evaluation of mesenteric ischaemia21, portal vein and hepatic artery thrombosis, but these application fields have been still in the experimental phases.
Conclusion
The CTA technique offers several advantages over conventional arteriography. Although other noninvasive modalities are gaining popularity, CTA is in many cases the definite method of the vessel pathology diagnosis and differential diagnosis. Although MR angiogra-phy is being established in this field, and has many advantages over CTA, like the lack of radiation exposure and there is no iodinated contrast material needed, CTA will continue to be the forefront of noninvasive vascular imaging due to its availability, relatively low cost and effectiveness in diagnosis and treatment planning.
References
1.	Balm R, Eikelboom BC, van Leeuwen MS, Noordzij J. Spiral CT angiography of the aorta. Eur] Vase Surg 1994; 8: 544-51.
2.	Gavant ML, Flick P, Menke P, Gold RE. CT aortography of thoracic aortic rupture. Am J Roentgenol 1996; 166: 955-61.
3.	Quint LE, Francis IR, Williams DM, Bass JC, Shea MJ, Frayer DL et al. Evaluation of thoracic aortic disease with the use of helical CT and multiplanar reconstructions: comparison with surgical findings. Radiology 1996; 201: 37-41.
4.	Zeman RK, Berman PM, Silverman PM, Davros WJ, Cooper C, Kladakis AO et al. Diagnosis of aortic dissection: value of helical CT with multiplanar reformation nad three-dimensional rendering. Arn J Roentgenol 1995; 164: 1375-80.
5.	Remy Jardin M, Remy J, Deschildre F, Artaud D, Beregi JP, Hossein Foucher C et al. Diagnosis of pulmonary embolism with spiral CT: comparison with pulmonary angiography and scintigraphy. Radiology 1996; 200: 600-706.
6.	Goodman LR, Lipchik RJ. Diagnosis of acute pulmonary embolism: time for a new approach. Radiology 1996; 199: 25-7.
7.	Mayo JR, Remy Jardin M, MLller NL, Remy J, Worsley DF, Hossein Foucher C et al. Pulmonary embolism: prospective comparison of spiral CT with ventilation-perfusion scintigraphy. Radiology 1997; 205: 447-52.
8.	Cross JJ, Kemp PM, Walsh CG, Flower CD, Dixon AK. A randomized trial of spiral CT and ventilation-perfusion scintigraphy for the diagnosis of pulmonary embolus. Clin Radiol 1998; 53: 177-82.
9.	Remy Jardin M, Louvegny S, Remy J, Artaud D, Deschildre F, Bauchart JJ et al. Acute central thromboembolic disease: posttherapeutic follow-up with spiral CT angiography. Radiology 1997; 203:173-80.
10.	Simoni G, Perrone R, Cittadini G Jr, De Caro G, Baiardi A, Civalleri D. Helical CT for the study of abdominal aortic aneurysm in patients undergoing conventional surgical repair. Eur j Vase Endovase Surg 1996; 12: 354-8.
11.	Van Hoe L, Baert AL, Gryspeerdt S, Marchai G, Lacroix H, Wilms G et al. Supra- and juxtarenal aneurysms of the abdominal aorta: preoperative assessment with thin-section spiral CT. Radiology 1996; 198: 443-8.
12.	Moritz JD, Rotermund S, Keating DP, Oestmann JW. Infrarenal abdominal aortic aneurysms: implications of CT evaluation of size and configuration for placement of endovascular aortic grafts. Radiology 1996; 198: 463-6.
13.	White RA, Donayre CE, Walot I, Kopchok GE, Wilson EP, Buwalda R et al. Preliminary clinical outcome and imaging criterion for endovascular prosthesis development in high-risk patients who have aortoiliac and traumatic arterial lesions. j Vase Surg 1996, 24: 556-69.
14.	Dorffner R, Thurnher S, Youssefzadeh S, Winkelbauer F, Hl)lzenbein T, Polterauer P et al. Spiral CT angiography in the assessment of abdominal aortic aneurysms after stent grafting:
Radiol Oncol 2000; 34(2): 137-43.
Kunst T ef ai. / Computed tomographic angiography of body vasculature
143
value of maximum intensity projections / Comput Assist Tomogr 1997, 21: 472-7.
15.	Mitty HA, Shapiro RS, Parsons RB, Silberzweig JE. Renovascular hypertension. Radiol Ciin Narth Am 1996; 34: 1017-36.
16.	Galanski M, Prokop M, Chavan A, Schaefer CM, Jandeleit K, Nischelsky JE. Renal arterial stenosis: helical CT angiography. Radialogy 1993; 189: 18592.
17.	Rubin GD, Dake MD, Napel S, Jeffrey RB Jr, McDonnell CH, Sommer FG et al. Spiral CT of renal artery stenosis: comparison of three-dimensional rendering technique. Radiology 1994; 190: 181-9.
18.	Beregi JP, Elkohen M, Deklunder G, Artaud D, Coullet JM, Wattinne L. Helical CT angiography compared with arteriography in the detection or renal artery stenosis. Am J Roentgenol 1996; 167: 495-501.
19.	Cochran ST, Krasny RM, Danovitch GM, Rajfer J, Barbaric ZM, Wilkinson A et al. Helical CT angiography for examination of living renal donors. Am J Roentgenol 1997; 168: 1569-73.
20.	Platt JF, Ellis JH, Korobkin M, Reige K. Helical CT evaluation of potential kidney donors: findings in 154 subjects. Am J Roenfgeno/ 1997; 169: 1325-30.
21.	Rubin GD, Dake MD, Napel SA, McDonnell CH, Jeffrey RB Jr. Three-dimensional CT angiography of the splanchnic vasculature. Radiology 1993; 189(P): 229.
22.	Freund M, Wesner F, Reibe F, Emde L, Hutzelmann A, Heller M. Spiral CT angiography for pre-operative planning in patients with epigastric tumors: comparison with arteriography. J Comp Assist Tomogr 1996; 20: 786-91.
23.	Kaneko K, Honda H, Hayashi T, Fukuya T, Ro T, Irie H et al. Helical CT evaluation of arterial invasion in pancreatic tumors: comparison with angiography. Abdom Imaging 1997; 22: 204-7.
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