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Vasa 2012; 41: 27 – 33 © 2012 Hans Huber Publishers, Hogrefe AG, Bern

L. Yang et al.: 64-slice spiral CT subtraction angiography in head and neck DOI: 10.1024/0301 – 1526/a000160

Original communication 27

Clinical application and technique of 64-slice spiral CT subtraction angiography in head and neck Lie Yang1, Xien Huang2, and Shaoyin Duan1,2 1

Department of Radiology, Teaching Hospital (Zhongshan), Fujian Medical University, Xiamen, China Zhongshan Hospital of Xiamen Unversity, Xiamen, China

2

Summary

Zusammenfassung

Background: To discuss the technique of 64-slice spiral CT subtraction angiography (64-SCTSA) in head and neck, and evaluate its clinical application. Patients and methods: 84 patients suspected of head-neck vascular diseases were examined with 64-SCTSA. The examination techniques, image quality and clinical application were retrospectively analyzed, and the diagnoses of 64-SCTSA were compared with those of surgery or DSA. Results: Eighty-four subjects were successfully examined with 64-SCTSA, whose scanning and imaging parameters are effective. Image quality was excellent in 51 cases (60.7 %), good in 29 (34.5 %) and acceptable in 4 (4.8 %). In the 84 subjects, 79 cases were found abnormal in blood vessel (58 in head and 21 in neck), of which 57 were confirmed by surgical operation or digital subtraction angiography (DSA). Conclusions: 64-SCTSA is a feasible technique with satisfactory image quality and has the advantages of showing the lesions of vasculature without shelter from bone. It can improve the diagnostic accuracy in head-neck vascular diseases.

Kraniale und zervikale 64-Zeilen-Spiral-CT Subtraktionsangiographie und deren klinische Anwendung Hintergrund: Diskussion der kranialen und zervikalen 64-Zeilen-Spiral-CT Subtraktionsangiographie (64-SCTSA); Technik und Beurteilung der klinischen Anwendung. Patienten und Methoden: 84 Patienten mit craniozervikalen Kreislauferkrankungen wurden mittels 64-SCTSA untersucht. Die Untersuchungstechnik, Bildqualität und klinische Anwendung wurde retrospektiv analysiert und die Diagnose von 64-SCTSA wurden mit derjenigen der Operation oder DSA verglichen. Ergebnisse: 84 Patienten wurden erfolgreich mit 64-SCTSA untersucht. Die Bildqualität war ausgezeichnet in 51 (60,7 %) Fällen, gut in 29 (34,5 %) Fällen und mittelmäßig in 4 (4,8 %) Fällen. Bei 79 von den 84 Fällen konnten Gefäßanomalien festgestellt werden (58 im Kopf und 21 im Hals), von denen 57 Fälle durch Operation oder DSA bestätigt wurden. Schlussfolgerungen: Durch die 64-SCTSA Technik wird der störende Einfluss der Knochenstruktur reduziert, wodurch sich die Darstellung der Gefäße verbessert und damit die Genauigkeit der bildgebenden Diagnostik erhöht.

Key words: Subtraction angiography, head-neck, tomography

Introduction As a non-invasive vascular imaging technique, CT angiography (CTA) has been extensively used in clinical practice. Authors found that the basicranial vascular lesions cannot be clearly or directly displayed with CTA due to the shelter from adjacent bony structures, while removing these structures with 3D cutting tools are not only time consuming, but also easy to cause image information loss [14, 16, 18, 25]. There are reports about bone-subtraction CT angiography, which can improve the observation of vascular anatomy and lesions [5, 9, 10, 13]. This article discusses the technique parameters and clinical application of 64-slice

spiral CT subtraction angiography (64-SCTSA) in head and neck.

Patients and methods Patients In our hospital, from May 1 2006 to May 31 2009, 84 patients (55 male, 29 female; age range 21 – 83 years, mean 49.1 ± 2.5) with suspected head-neck vascular disease were examined with 64-SCTSA. Examination techniques were retrospectively analyzed, as well as both image quality and clinical application. Equipments and technique 64-slice spiral CT (Light speed VCT, GE, USA), with double-high-pressure

syring (Stellant, Medrad Co., USA) and Contrast medium (Omnipaque 300 mgI/mL, shanghai affiliate corporation of GE) was used. Examination process is as follows: 1. Perform CT pre-scan with low-dose (120 KV, 30 mA) after intravenous injection of Omnipaque 20 ml (A tube) + Normal saline 10 ml (B tube) to get the timedensity curve of intravascular contrast medium at the internal carotid artery and its peak time, together with the delayed scanning time ,that is, peak time plus 4 – 6 seconds [12, 13]. 2. Complete two scanning sequences with the same parameters and range from the aortic arch to the top of skull (the scanning parameters include tube voltage of 120 KV, tube current of 250 mA, pitch of 1.375 and

L. Yang et al.: 64-slice spiral CT subtraction angiography in head and neck


28 Original communication

slice thickness of 0.625 mm). The first scanning sequence was performed at the same time or 2 – 3 seconds after intravenous injection of Omnipaque 80 ml (A tube) + Normal saline 20 ml (B tube). The second sequence automatically started according to the determined delayed scanning time. 3. Obtain two scanning data, transfer them to AW4.2 workstation to perform 64-SCTSA. 3D images of 64-SCTSA were obtained with volume rendering (VR), maximum density projection (MIP), multi-planar reconstruction (MPR) and curved planar reformation (CPR). Image quality was graded: ķ “excellent”, vascular structure clearly shown without other structures artifacts; ĸ “good”, vascular structure clearly shown with some little bony structures and other artifacts; Ĺ “acceptable”, vascular structure clearly shown with a good number of bony structures and artifacts; ĺ “insufficient”, vascular structure poorly shown with more bony structures and artifacts. Image evaluation and criteria were discussed, 64-SCTSA diagnoses were compared with those of surgery or digital subtraction angiography (DSA).

Figure 1: The whole and local 3D-images in head and neck of 64-SCTSA showing bony structures successfully eliminated and the internal carotid artery and the vertebral artery and their branches clearly displayed, without obstruction or interference from the skull base.

Results Eighty-four patients were successfully examined without being subjected to contrast agent allergy or improper scanning technique. 3D images of 64-SCTSA clearly and directly showed the internal carotid artery (ICA), vertebral artery (VA) and other headneck vascular structures and lesions without shelters from bone or other structures (Fig. 1 – 3). Image quality was excellent in 51 cases (51/84, 60.7 %), good in 29 (29/84, 34.5 %), acceptable in 4 (4/84, 4.8 %) and insufficient in zero. In these 84 cases, 5 cases were normal and 79 were found to have vas-

Figure 2: Aneurysm of anterior communicating artery (ACoA) was clearly depicted with 64-SCTSA, with the parent artery, the neck and the body of aneurysm clearly displayed (white arrow on the Fig. 2 A); DSA showing the delineation of ACoA aneurysm very similar to that of 64-SCTSA.

cular abnormality, among which 58 were in the head (38 cases with cerebral aneurysms, with the maximum of 17.2 mm × 11.5 mm and minimum of 1.8 mm × 2.6 mm, 15 with intracranial arteriovenous malformation (AVM), 4 with intracranial vascular stenosis or occlusions and 1 with cavernous-ophthalmic

artery fistula). 21 cases were in the neck (11 with carotid arterial sclerosis stenosis, 8 with VA sclerosis stenosis and 2 with VA aneurysms). There were 57 patients (32 cases with aneurysms, 10 with AVM and 15 with vascular stenosis) proved by surgical operation or DSA, of which 21 cases were directly operated relying on the




diagnosis of 64-SCTSA. The diagnosis of 64-SCTSA was basically consistent with that of surgery or DSA (Fig. 2 – 4). In the 38 patients with cerebral aneurysms, 2 cases were suspected to have another aneurysm which by DSA was proved to be a false sign due to overlap of vessels by 3D images of 64-SCTSA (Fig. 5); 2 cases with a second aneurysms missed with DSA and 1 with aneurysm of ICA missed with CTA were all clearly shown with 64-SCTSA (Fig. 6, 7). According to the automatic dose calculations performed automatically by the system, an average volume computed tomography dose index (CTDIvol) of 19.35 mGy and an average dose length product (DLP) of 1.35 Gy cm were applied for the 64-SCTSA in head and neck acquisition. No patient suffered radiation-induced temporary hair loss or other types of radiation complications.

Discussion Measurement of the peak time If CT scan can be completed within the peak time of intravascular contrast agent in the artery, 3D-images of vascular reconstruction will be the optimal and can effectively avoid the interference from different heart-cerebral circulation time caused by different individuals and heart-function, which is crucial in obtaining high quality images. In our study, the peak time in carotid artery for most subjects was within 16 – 20 seconds, with the biggest difference of 8 seconds, which was consistent with the report [5].In our study, the second scanning sequence was finished around the peak time of carotid artery plus 4 – 6 seconds, the quality of 3D images was satisfactory [2, 4]. It suggests that the measurement of the peak time is indispensable for guaranteeing the image quality of 64-SCTSA.

Subtraction angiography and imaging parameters Because the first scanning sequence was performed far before the peak time of intravascular contrast agent was reached, we obtained the image data equivalent to plain scan data (assumed to be A) because the vessels were not filled with contrast agent. The second scanning sequence was just at the peak time, the image data include that of plain scan and of vessels containing contrast agent (assumed to be A + B). On the AW4.2

workstation with Add/Sub software, the data of the first sequence was subtracted from that of the second, the image data of vessels was left and saved as a new sequence (B), which was used to perform 3D images and show vessels alone. As for the scanning sequence, the following factors should be taken into consideration: 1. The interval of the first and second scanning sequence should not be less than 8 seconds, otherwise image information may be lost after subtraction. 2. The second scanning

Figure 3: 64-SCTSA can clearly display the aneurysm of internal carotid artery (ICA) closely adjacent to the base of skull, without obstruction from skull base, the parent artery, neck and dome of the aneurysm are clearly delineated (white arrow on the Fig. 3 A); DSA showing the delineation of ICA aneurysm close to the base of skull very similar to that of 64-SCTSA. The image of CTA cannot clearly display the aneurysm (thick arrow on Fig. 3 C).

Figure 4: Aneurysm of right vertebral artery (VA) sufﬁciently delineated on 64-SCTSA image (white arrow on the Fig. 4 A). Meanwhile, left VA is also clearly displayed, which is an advantage of 64-SCTSA comparison with DSA; DSA showing the delineation of aneurysm of left VA very similar to that of 64-SCTSA.




sequence should be performed at the peak time of carotid artery plus 4 – 6 seconds, which should be an integral multiple of 0.4. Only in this way can the same position of the X-tube at two scanning sequences be guaranteed and the data of the two sequences be subtracted from one another. 3. It is necessary to fix patient’s head appropriately giving continued information about the examination process to gain his cooperation. Characteristics of 64-SCTSA images 64-SCTSA can clearly show the entire blood vessels of head-neck and/or lesions without the shelter from bone from any direction. It can quite easily measure the size of small aneurysm and observe its spatial relationship, including the parent artery, the neck and body of the aneurysm, which are not easily to be clearly shown by DSA. The rotational observation of aneurysms from multi-directions on the 64-SCTSA images enables surgeons to make a better choice of surgical approach, arterial clipping or interventional embolization material [19, 20, 24]. Our study suggests that 64-SCTSA can display the concealed vascular pathologies close to the skull base and exclude false positive results caused by vessel distortion and curves, which are the usual causes of missed diagnosis or over-diagnosis with DSA or CTA. However, it is difficult for CTA to manually remove bony structures exactly, because there is often excessive or inadequate bone removel due to similar density between vessel and bone. If the density threshold of bony removel is too high, imaging cannot show small aneurysms or small vessels. If it is too low, small aneurysms may be hidden by obstructing structures. 64-SCTSA can compensate the above shortcomings by using subtraction technique.

Clinical application and related comparisons Autopsy studies showed that the incidence of cerebral aneurysms is about 0.2 % – 9.9 %, while the mortality rate of aneurysm rupture and spontaneous subarachnoid hemorrhage (SAH) in 24 h can run up to 50 % causing serious disablement. It is crucial to make an early diagnosis and choose effective therapy [6, 12]. 64-SCTSA

has been widely used as a reliable examining tool to discover the primary cause of SAH or intra-cerebral hematoma, including the diagnosis of cerebral aneurysms, intracranial arteriovenous malformation, vascular occlusion and arteriosclerotic stenosis, et al. As a gold standard of diagnosing the vascular diseases, DSA is expensive, invasive and timeconsuming, and it cannot be carried

Figure 5: Patient with the right middle cerebral artery (MCA) aneurysm (thick arrow on Fig. 5 A, D), another “Aneurysm of ACoA” was suspected with DSA (thin arrows on the Fig. 5 A, B) and shown on the image of CTA (thin arrow on Fig. 5 C), but these proved to be false signs from overlap of vessels in 3D images of 64-SCTSA (thick arrow on Fig. 5 D).

Figure 6: MCA aneurysm being missed by DSA and showing unclear delineation being considered the overlap of vessels (white arrow on Fig. 6 A). 64-SCTSA clearly displays the shape of middle cerebral artery (MCA) aneurysm, which is diagnosed (white arrow on Fig. 6 B, C).




out within 5 hours after intra-cerebral bleeding, threatening to induce recurrent bleeding. In our study, missed diagnosis and over-diagnosis were rarely occurred in diagnosing aneurysm. MRA without ionizing radiation, including the CE-MRA and TOF-MRA, do not differ regarding the evaluation of normal intracranial vessels [1]. But MRA, with low spatial resolution, cannot clearly show the bone structures, and it is sensitive to the flowing situation of blood, may cause image artifacts or signal loss and cannot detect aneurysm in the region of swirl or slow blood flow [7, 8, 21]. However, we have to believe that most diagnostic information is already presented in the un-subtracted CTA, which has a high diagnostic accuracy. But the subtracted CTA can give additional information regarding the abnormality of ICA and the vessels near the base of skull, provide more anatomic basics to the diagnosis and treatment of vascular diseases, and improve clinical effect [11, 17, 22, 26]. Prospects and disadvantages 64-SCTSA has enriched the techniques of CTA and improved the diagnostic accuracy of vascular anatomy. It is beneficial to the study of arterial disease, such as aneurysms, AVM, arterial stenosis and so on. By increasing venous scanning sequences, we can obtain venous images, from which venous diseases such as venous thrombosis, AVM, cavernous fistulae will be more clearly shown and correctly diagnosed [15, 24]. However, 64-SCTSA has some limitations. For example, stents, coils, calcified plaques of the arterial wall and surgical clips cannot be shown because they become extinct. Moreover, slight movement may lead to incomplete bone removal and affect the diagnosis [26]. However, the scanning data of 64-SCTSA can be repeatedly used,

Figure 7: 64-SCTSA clearly shows the complete shape of the internal carotid artery (ICA) aneurysm close to the base of skull (white arrow on on Fig. 7 A); on CTA imaging the ICA aneurysm is hardly visible due to obstruction of the skull base.

and the above drawbacks can be compensated by referring to the thin-slice source images and CTA without bone subtraction to avoid diagnostic mistakes resulting from any data post-processing. Radiation dose and complications For the additional pre-contrast scan, with the same radiation dose as the post-contrast scan, there is a double radiation dose to the patient compared with non-subtraction CTA. However, the total radiation dose of examination is far from 3 – 5 Gy, which possible leads to radiationinduced temporary hair loss. As the examination is only for once and cannot be repeated within 3 weeks [3], it is predictable that no patients will be found to have radiation-induced temporary hair loss or other types of radiation complications in our study. We use the same radiation dose in both scanning sequences for the purpose of ensuring the 3Dimage quality of 64-SCTSA. When using a low-dose non-contrast scan for the acquisition of the bone mask, we find 3D-images showing an irregular or rough blood vessel surface, possibly impeding correct

diagnosis. The cause of rough vessel surface deserves future clarification. As a new technique of bone removal in CT angiography, the application of dual energy CTA typically has the advantages of low radiation dose and rapid execution [23]. But we cannot be sure when the 3D images show a rough blood vessel surface, if so, it may be due to a different scan. If not, a low-dose non-contrast scan for the acquisition should be performed to decrease the radiation dose.

Acknowledgment We would like to express our thanks for the support of Xiamen Board of Health’s Medical Research Program (WSK 0622) and National Natural Science Foundation (81071214), China.

Conflicts of interest There are no conflicts of interest existing.




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Correspondence address Prof. Shaoyin Duan, PhD Medical imaging Zhongshan Hospital of Xiamen Unversity No.209 South Hubin Road CN-361004 Xiamen P. R. China [email protected]

Submitted: 03.05.2011 Accepted after revision: 08.07.2011