CTA source images

Coutts SB, Lev MH, Eliasziw M, Roccatagliata L, Hill MD, Schwamm LH, Pexman JH, Koroshetz WJ, Hudon ME, Buchan AM, Gonzalez RG, Demchuk AM. ASPECTS on CTA source images versus unenhanced CT added value in predicting final infarct extent and clinical outcome. Stroke 2004 35 2472-2476. 

Review of postcontrast CTA source images might provide a good estimate of whole-brain perfusion." If time allows, MR or CT perfusion maps are obtained to characterize more accurately the ischemic penumbra." Careful but expedited preprocedural analysis of the CTA, done in parallel with transport of the patient to the treatment area, may be extremely helpful in establishing the presence of anatomic variants (e.g., bovine aortic arch) or pathological states (e.g., vessel origin or carotid bifurcation disease) prior to the catheterization procedure. 

The CTA protocol described in this chapter was designed to provide diagnostically useful information about both the vascular and parenchymal phases of brain enhancement. The administration of contrast serves two purposes first, to visualize acute clot in the MCA, distal internal carotid artery (ICA), basilar artery, and other major circle of Willis vessels (Fig. 4.1) and second, to better delineate potentially salvageable, underperfused, ischemic areas of the brain that are at risk for full infarction if circulation is not restored. More specifically, this includes those areas with a relative lack of contrast enhancement on CTA source images (CTA-Sl). Moreover, CTA-Sl can also be of value in suggesting otherwise unsuspected... 

Fig. 4.16 (a) Axial CTA source images demonstrate a right middle cerebral artery saccular aneurysm, (b) Axial and coronal MIP, and volume-rendered image confirm aneurysm at the right middle cerebral artery... 

An early report from our group indicated that, in the absence of early recanalization, CTA-Sl typically defines minimal final infarct size and, hence, like DWI and thresholded CBF maps (Fig.5.5, 5.6), can be used to identify infarct core in the acute setting [34] (Figs. 5.5, 5.6). Coregistration and subtraction of the conventional, unenhanced CT brain images from the axial, post contrast CTA source images should result in quantitative blood volume maps of the entire brain [15, 27, 70]. CTA-SI subtraction maps, obtained by coregistration and subtraction of the unenhanced head CT... 

Finally, it is noteworthy that, as with DWI, not every acute CTA-SI hypodense ischemic lesion is destined to infarct [176, 177]. In the presence of early complete recanalization, sometimes dramatic sparing of regions with reduced blood pool on CTA source images can occur (Fig. 5.8). This suggests that, as with CBV, CBF, and DWI, time-dependent thresholds exist for... 

Studies using various imaging modalities (Xe-enhanced CT, MRI DWI, CTA source images, and CTP) have demonstrated that pretreatment core infarct size predicts the clinical response to reperfusion, and that core infarct volume less than 70-100 mL may be an effective treatment target... 

CTA source image hypoattenuation delineates tissue with CBV depression, and hence infarct core, under steady-state conditions. However, the steady-state assumption may not hold with newer generation multidetector CT scanners... 

Hu R, Yoo AJ, Hakimelahi R, Lev MH, Nogueira RG, Hirsch JA, Gonzalez RG, Schaefer PW (2010) CTA source images in the era of fast, volume CT scanning are they still DWI weighted International Stroke Conference, San Antonio, TX... 

Subsequently, the axial CTA-SIs are reviewed, typically at the scanner console. Large, proximal circle of Willis occlusions, such as top-of-carotid T-lesions, are easily recognizable, even from the axial source images, and the stroke team can be immediately notified. Simultaneously, at most modem scanner consoles,... 

Puchner S, Popovic M, Wolf F et al (2009) Multidetector CTA in the quantification of internal carotid artery stenosis value of different reformation techniques and axial source images compared with selective carotid arteriography. J Endovasc Ther 16 336-342. 

The technical considerations and interpretation of the second portion of the acute stroke protocol, CTA, is discussed in detail in Chap. 4. Importantly, however, the source images from the CTA vascular acquisition (CTA-SI) also supply clinically relevant data concerning tissue level perfusion. It has been theoretically modeled that the CTA-SI are predominantly blood volume, rather than blood flow weighted [20, 27,70], The potential utihty of the CTA-SI series in the assessment of brain perfusion is discussed in detail below. This perfused blood volume technique requires the assumption of an approximately steady state level of contrast during the period of image acquisition [27], It is for this reason - in order to approach a steady state - that protocols call for a biphasic contrast injection to achieve a better approximation of the steady state [71, 72]. More complex methods of achieving uniform contrast concentration with smaller doses have been proposed that may eventually become standard, such as exponentially decelerated injection rates [73] and biphasic boluses constructed after analysis of test bolus kinetics [72, 74]. 

Fig. 5.5 Infarct conspicuity on source images from the CTA vascular acquisition (CTA-SI). An infarct in the left MCA distribution is more conspicuous on the CTA-SI image (top right, arrows) than the unenhanced CT (top left) performed in the...

Fig. 20.2a-d. Dual-source coronary CTA performed in three patients with AF, causing an absolute arrhythmic heartbeat during the scan. In the first patient, image quality is optimal, and despite the absolute arrhythmia during scanning, no motion artifacts can be seen in the volume-rendered images (a, b). In the second patient with absolute arrhythmia, a minor step... 

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