3D Imaging Delivers Clinical Benefits

Interventional neuroradiology is rapidly breaking new ground in the treatment of AVM's, subarachnoidal hemorrhages and intracranial aneurysms – in addition, successful endovascular therapy depends on access to high precision images showing the angio-architecture of the structures. 3D Imaging excels by offering a range of views to provide even the most difficult angles.

At Dalcross Private Hospital, we have just installed the GE Advantx LCV+ with 3D Vascular Imaging, bringing this advanced technology to our patients. Recognised as having Australia's leading private Neurosurgical Unit, this installation keeps Dalcross at the forefront of developments.

Advanced applications possible on this equipment include:

• Navigator – intra-luminal interactive viewing
  
• Transparency – allows optimal anotomical viewing without obscuring relevant pathology
  
• Measure Distance and Volume – both distance and volume are available without calibration
  
• Advanced Vessel Analysis – sophisticated stenosis sizing algorithm aids stent size selection
  
• Coils & Clips – reconstruction and merging of interventional coils and clips

Patient comfort and safety is also considered – these advanced applications are achieved in the shortest time possible, with the least radiation dose possible. We will examine the impact of 3D Imaging on interventional neuroradiology, and the role it plays in the therapeutic decision making process.

What Are The Clinical Advantages With 3D Reconstruction?

At one time 3D was considered a bit of a toy – performed by a few teams wearing special glasses. I now consider 3D to be very useful in interventional neuroangiography. In fact, we believe it is a fantastic, irreplaceable tool, especially in the treatment of intracranial aneurysms. Nothing can replace the third dimension in this type of procedure where very precise quantitative analysis must be available. In fact, 3D has brought such precision to vascular imaging that in certain cases we are prepared to risk transferring the patient to the new LCV+ to obtain the 3D information – in some cases it is that critical.

Describe The 3D Acquisition And Processing Parameters

The acquisition parameters are identical each time – the 2D spin is acquired with a gantry rotation of 200 degrees, at a speed of 40 degrees per second. Once the rotation acquisition is finished, the digital data is sent automatically to the workstation. This phase requires no manual intervention at all from the operator – in a short 8-10 minutes the 3D images automatically appear in the workstation.

How Do You Use The 3D Data And Tools?

There are several display modes and tools. We usually start with MIP (Maximum Intensity Projection) which provides a simple and efficient way to display the 3D images. Surface rendering on the other hand is the most aesthetic, but it tends to soften certain angles and sometimes doesn't reflect reality in terms of the neck of aneurysms. It does, however, give first rate relief information and what we do in practice is to always use Surface Rendering together with MIP to perform the analysis. We also use reformatted cross sections to define segments for quantitative analysis – fundamental for treating aneurysms because we can measure the sac in its different dimensions, measure the neck, and thus immediately select the optimal size of the coils we are going to put in the sac.

This minimises the risk of changing the coils during the intervention, and brings the benefit of avoiding complications while reducing the treatment cost. The Navigator tool displays the arterial lumen as it would be seen from inside the vessel, and with it we can tell whether an aneurysm is open or closed, and whether or not blood flow is still entering the sac. It cannot, however show us the coils directly in the aneurysmal cavity, since the coils are not visible in the 3D images. Navigator is also interesting for dissections of the arterial wall.

And 3D Repositioning – Is This A Useful Feature?

3D repositioning is very useful, and works well. The technique allows us to work directly on the console to select angulations. When we have defined the best angle at the workstation these co-ordinateds are sent directly to the system – and at the push of a button the gantry moves automatically to that position. We even have information at the workstation as to whether the angulation is feasible or not. So we can immediately deduce from the workstation the ideal fluoroscopic angulation to see the neck of an aneurysm. It is also useful where there are vascular lesions such as dissections of the cartoid arteries which are difficult to analyse. The same applies to other malformations and certain fistulae where the 2D angulation derived from the 3D angio can give us a more meaningful image for the referring physician.

Have You Noticed A Reduction In X-Ray Dose Compared To Your Former Techniques?

With 3D angiography, we obtain a vast number of projections from a single contrast injection so we no longer have to perform aquisitions from multiple projections. There is no doubt that we can now reduce the number of total acquisitions, and thus reduce both contrast media and radiation dose. The new filters have also considerably helped reduce the patient skin dose, while maintaining excellent image quality.

Case Study

This case study was performed using the GE Advantx LCV+ with 3D Vascular Imaging. This takes 2D digital subtraction angiographic (DSA) data acquired during a high-speed 200 degree spin, and automatically reconstructs a 3D model of that data. This 3D model allows extensive processing and virtually unlimited projections for superb case assessment.

Case History

A 69-year-old female, with an incidentally discovered large middle cerebral artery (MCA) trifurcation aneurysm,underwent cerebral angiography at an outside institution. Routine high resolution 2D DSA images from the outside institution were not adequate to show the relationship of the aneurysm to the different branches of the trifurcation and the detailed anatomy of the aneurysm neck. This patient was transferred to the Neurosurgical Unit for operative treatment and pre-operative reassessment of the aneurysm, using 3D rotational angiography.

Case Procedure

Prior to surgery, the patient underwent routine assessment of intracranial aneurysms. This consists of a standard bi-plane DSA sequence in AP and lateral projections, followed by a single 3D rotational sequence. The complex anatomy of the MCA trifurcation anatomy was then critically assessed at the Advantage Workstation. The ability to manipulate the vasculature on the workstation in real-time allows the operator to obtain rapid, precise anatomical information of the vasculature, without subjecting the patient to multiple injections of contrast and prolonged catheter time.

Summary

The 3D images in this case provided a complex understanding of this complex aneurysm prior to definitive operative treatment. The aneurysm neck was found to arise from a tight bend in the most medial branch of the trifurcation vessels. The large dome was found to project over the middle cerebral artery and the bifurcation of the other twobranches of the trifurcation. This information was invaluable for surgical planning. Operative results confirmed the anatomy which was demonstrated on 3D images.

Carotid Ophthalmic Aneurysms And X-Ray In-Room 3D

3D X-ray Spin Angiography is an X-ray technique available on any GE Angiographic system. The patient is iso-centred to the gantry, a bolus of contrast agent is injected into the artery and the system performs an automatic spin of 200 degrees in just over 5 seconds. There is an initial spin to form the mask sequence, followed by another spin for the images. Vessels and also Coils and Clips can then be rendered from these sequences in 90 seconds.

Case History

A 50-year old female was admitted to another Hospital with a history of dizziness and other ill-defined symptoms. After MR imaging, she was found to have an un-ruptured aneurysm at the carotid ophthalmic junction and was referred for Surgery. During theoperation, it was found to be impossible to clip the aneurysm due to its location, which was partially intra-cavernous. Later, the patient developed headaches thought to be related to compression of the trigeminal nerve – and thereafter she refused any further surgery. Two years later, she attended the Department of Neuroradiology where she had selective 3D X-ray Angiography and is now waiting for endovascular therapy using Onyx.

Case Procedure

The patient was catheterised and had selective Subtracted Angiography of the carotid artery, followed by a 3D Spin. To perform the spin, 18 mls of 300 mg Iodine-based contrast agent were injected into the carotid artery using an auto-injector and the images were acquired at the Low Dose setting. The reconstructed 3D image was then displayed 90 seconds later on the in-room monitor.

Summary