In parallel with revolutionary advancements in the techniques and tools for endovascular treatment of cerebrovascular diseases has been a dramatic enrichment in the imaging capabilities of x-ray angiographic equipment. To one who started trying to perform endovascular interventions at a time when angiographic studies were recorded on film, and when a road-map was only something one used to travel, the imaging and fluoroscopic visualization capacities of current flat detector C-arm systems is truly a thing of wonder. The modern angiography suite allows 2D and 3D images of the intracranial and spinal vasculature to be obtained with superior spatial and temporal (2D) resolution to any other modality. ¹ New applications exploiting the ability to obtain CT-like images of both high-contrast objects and soft tissue now make it possible to determine key features of implantable devices, eg, wall apposition of stents as well as to obtain both steady-state and dynamic measurements of tissue perfusion parameters. In this issue of the AJNR News Digest, recent publications exploring and describing these applications are highlighted.

Papers by Wakhloo, Thielen, Sheen, and their colleagues describe the use of high spatial resolution flat detector imaging to evaluate stents, complex vascular abnormalities, and arterial stenosis; papers by Royalty, Mordasini, Struffert, and Gounis and their colleagues describe preclinical and clinical experiences measuring perfusion parameters.

The article by Wakhloo shows the ability to evaluate stent configuration, as well as the degree of stent expansion and wall apposition. This is important because incomplete wall apposition, either due to kinking of a stent or incomplete stent expansion, has been linked to thromboembolic complications and stent migration.² The ability to clearly see these features during an intervention should translate into improvements in both the safety and efficacy of procedures where stents are utilized.

Sheen and colleagues provide evidence to show that, with proper technique, vascular abnormalities involving arteries at the level of the Circle of Willis can be detected and characterized using 3D acquisitions done in conjunction with the IV injection of contrast medium. In our practice this technique is often used for postoperative evaluation of aneurysms treated by clipping, and for follow-up of patients with coiled aneurysms who are not able to undergo MR imaging. Sheen’s manuscript also points out the potential reduction in radiation exposure that may be achieved using flat detector CT instead of MDCT. While understanding the full capability and optimal utilization of this technique will require larger studies, it seems likely that the combination of superior high-contrast spatial resolution and the ability to obtain images at very small x-ray doses may, in many instances, make this the indicated modality of choice for these types of evaluations.

Thielen and colleagues reported their experience using intra-arterial injections of contrast in conjunction with 3D C-arm CT acquisitions for evaluations of spinal dural AVF. Their report highlights the added

information concerning the location of the fistula site, along with its relationships to adjacent bony and soft tissue, that is gained though use of these high spatial resolution volumetric reconstructions as compared with conventional 2D examinations. In earlier publications members of this same group had documented the considerable savings in radiation dose gained by using 3D acquisitions instead of biplane 2D DSA studies.³

Papers by Royalty, Mordasini, Struffert and Gounis and their colleagues all deal with evaluating the feasibility, using flat detector C-arm systems, to measure tissue perfusion parameters. Royalty describes dynamic measurements of CBF and CBV using a high-speed multirotation acquisition done in conjunction with a single injection of contrast. The results presented show both the feasibility and the limitations of obtaining these measurements using flat detector C-arm systems. Royalty also emphasizes the likelihood that oncoming hardware and software advances will significantly decrease or eliminate some of these limitations. The papers by Mordasini and by Struffert and colleagues both show the feasibility of obtaining steady-state measurements of CBV in patients with acute ischemic and hemorrhagic strokes. Like Royalty, these authors point out the current limitations of the technique while also commenting on limitations that can likely be rectified using available technology, eg, motion correction algorithms. Gounis and colleagues reported the results of a study in canines with an acute ischemic stroke, correlating the volume of CBV abnormalities as measured with flat detector C-arm CT and with conventional MR ADC maps. As one would predict, the ADC measurements were shown to be superior to the flat detector C-arm measurements. Still, this publication shows the potential of this technique and, like Mordasini, Stuffert, and Royalty, Gounis describes short-term improvements that likely will significantly improve the quality of the flat detector perfusion measurements, eg, improved detector technology.

The angiographic suite is rapidly becoming an environment where patients with both acute ischemic and hemorrhagic strokes can be diagnosed, triaged as to best treatment options, and, if appropriate, be treated using endovascular techniques. While there is very legitimate debate regarding the value added by perfusion measurements in patients with an acute ischemic stroke, much of this hinges not on the information provided but on the cost in time required to obtain these measurements. Having the ability to acquire all needed imaging studies—ie, noncontrast CT, contrast-enhanced CT, 3D vascular volume, and perfusion parameters—using a single modality in a single room with a very acceptable x-ray and contrast medium dose might, by saving precious time, and perhaps also by improving patient selection for treatment, improve the outcomes of these patients.

References

1. Grist TM, Mistretta CA, Strother CM, et al. Time-resolved angiography: past, present, and future. J Magn Reson Imaging 2012;36:1273–86. doi: 10.1002/jmri.23646
2. Heller RS, Malek AM. Delivery technique plays an important role in determining vessel wall apposition of the Enterprise self-expanding intracranial stent. J Neurointervent Surg 2011; 3:340–43. doi: jnis.2010.004499
3. Schueler BA, Kallmes DF, Cloft HJ. 3D cerebral angiography: radiation dose comparision with digital subtraction angiography. AJNR Am J Neuroradiol 2005; 26:1898–1901

 

Image modified from: Struffert T, Deuerling-Zheng Y, Engelhorn T, et al. Feasibility of Cerebral Blood Volume Mapping by Flat Panel Detector CT in the Angiography Suite: First Experience in Patients with Acute Middle Cerebral Artery Occlusions.