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South Eastern Sydney Local Health District
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Arteriovenous Malformations

What is an AVM?

Arteriovenous Malformations (AVM) are rare, abnormal tangles of blood vessels. How they form is not fully understood, but they are believed to be formed early during a person's development before their birth.

An AVM can occur almost anywhere in the body, but is most concerning if it occurs inside the brain ("cerebral AVM") because an AVM is a weak point which can unexpectedly cause internal bleeding. If a cerebral AVM bleeds, the result can be a stroke.

How to treat AVMs:

Cerebral AVMs can sometimes be treated using surgery if they are not too deep inside the brain or not too close to critical parts of the brain. Radiosurgery (exposure of the AVM to high intensity X-Rays) is a less invasive treatment, even able to reach AVMs not amenable to surgery.

Cerebral AVMs are diagnosed by visualising them in 3-dimensions using an X-Ray CT scan, an MRI scan or a rotational angiogram of the brain. These images can also be used to develop a radiosurgery treatment plan - a map of where inside the head, the beams of high intensity X-Rays should be aimed.

Current AVM research:

Associate/Professor Smee is currently undertaking research in this area including a specialised project led by a Medical Physicist.  The aim of this project is to allow the information from images of AVMs obtained using these three imaging methods to be combined seamlessly in a single image to assist in treatment planning.

What does this mean?

When treating Arteriovenous Malformations (AVM), a map of the intended radiation dose ("treatment plan") is created using a 3-dimensional stack of slices ("tomographic images") of the patient's head obtained using X-ray CT and MRI (magnetic resonance imaging). When data are in the form of tomographic slices, it also allows sophisticated computer analysis ("segmentation") of the 3-dimensional structure of individual internal structures such as the AVMs.

 

Magnetic Resonance Imaging Magnetic Resonance Imaging
Magnetic Resonance Imaging
of an AVM (green tangle of
blood vessels briefly circled in green)
Animation of a segmentation of MRI image of an AVM
(clump of blood vessels briefly circled in yellow).

Unfortunately, although X-ray CT and MRI provide tomographic slices suitable for treatment planning, the resolution (fineness) of the image is not quite good enough to show the smallest blood vessels in the AVM, so drawing the outer boundary of the target volume containing the AVM for treatment planning purposes, is a little uncertain.

To improve the certainty, the Radiation Oncologist will order a higher resolution X-ray angiogram which is taken from two different viewpoints - front-on (anterior-posterior) and sideways (lateral). In these images, even the small vessels are visible, making the radiosurgeon's job more certain. These images can be scanned into the planning system software and super-imposed on the MRI and X-ray CT images, so a more certain boundary can be drawn around the AVM.

 
                           X-ray angiogram

                             Above: X-ray angiogram taken from two viewpoints

These images are high resolution, but they are not full 3-dimensional images, so there is still some uncertainty in the boundary. To get a better idea of the shape of the AVM in 3-dimensions, a "rotational angiogram" can be ordered. This is similar in procedure to the high resolution X-ray angiogram, except that the image is now taken from 100 viewpoints as the X-ray camera rotates around the patient's head.

These images now give accurate information about the shape of the AVM in 3-dimensions, but in this format, the 100 images cannot be scanned into the planning system because they are all from different angles. To do this, the rotational angiogram must be converted into a form similar to the format of the 3-dimensional stack of tomographic images provided by MRI and X-ray CT.

 

 

This project is concerned with taking the rotational angiograms and converting them into the 3-dimensional tomographic format suitable for use in the planning system software, while retaining the high resolution provided by the original X-ray angiogram.

 

This will further decrease the uncertainty in drawing the boundary of the target volume containing the AVM for treatment planning purposes. It would also allow segmentation and other sophisticated analysis of the high resolution X-ray angiograms.

Rotational angiogram
  Rotational angiogram