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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3643_Библиотеки_им_академика_М_И_Перельмана.pdf
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Fig. 7.13 CTA is the only current angiographic method that allows
such high-resolution images of contrast-fi lled vessels, plaque, and surrounding soft tissues
Fig. 7.12 When the residual lumen is elongated in the axial plane, the stenosis at its narrowest point can be measured with much more accuracy
than on angiograms
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Fig. 7.14 In the case of very coarse wall calcifi cations, properly wide window level settings can reduce beam-hardening artifacts
Fig. 7.15 Axial sections are
obtained by using a postprocessing reconstruction
technique, such as MIP and/or
SSD reconstruction (MIP is more
reliable than SSD)
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Fig. 7.16 In very severe stenosis, the decrease in distal ICA diameter
precludes an accurate measurement of the degree of stenosis by the
NASCET method and usually leads to a classifi cation of cases with
ICA diameter lower than that of the external carotid artery as near
occlusion (in image ACI, ACE - Internal and External Carotid Arteries,
PRE-OCL - Preocclusion)
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Fig. 7.17 MPR: in cases of very short stenosis, the assessment of the stenosis on axial images can become diffi cult, in which cases MIP recon-
structions can help
Fig. 7.18 In cases of tortuous vessels, make interpretation of images diffi cult; MIP reconstructions can help
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Fig. 7.19 MIP: calcifi cations are easily detected on MIP and can artifi cially shrink the diameter of the artery, but this might theoretically be
avoided with multiple view angles
Fig. 7.20 MIP: the readers attempts to select a windowing producing the best available edge detection for each vessel
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Fig. 7.21 The advantage of SSD resides in the possibility of moving, rotating, and adjusting for tilt
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Fig. 7.22 Even in the absence of calcifi cation, SSD frequently underestimated the degree of stenosis (indicated by arrow in image), probably due
to the arbitrary selection of the lower threshold
Fig. 7.23 SSD, MPR, and MIP reconstructions: accuracy is reduced on SSD reconstruction if extensive calcifi cation is present, but this limitation
can be avoided when MPR and MIP reconstructions are used
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Fig. 7.24 When using an automated 3D CTA analysis program, several misregistrations of the enhanced carotid artery lumen were noticed
Fig. 7.25 The major disadvantage of the technique is represented by the need to post-process data to remove calcifi cations, veins, and bone struc-
tures from the images
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Fig. 7.26 Stents in the carotid artery may cause severe streak artifacts
Fig. 7.27 Obese patients are suboptimally imaged
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Fig. 7.28 Motion artifacts (as shown by arrow in image)
7 Diagnostic Approach to Cerebrovascular Disease: CT and MRI