Diagnostic Tools

Advanced Imaging Techniques at Hoag Hospital

The evolution and success of Gamma Knife Radiosurgery is directly dependent on the imaging modalities available to determine the location of the tumor or AVM. A GK treatment center must have the accompanying state-of-the-art imaging modalities and neuro-oncologic radiology specialists in order to maximize the efficacy of the GK treatment unit and team. Hoag Hospital is fortunate to have both the technology and the staffing to collaborate on neurological and Gamma Knife patients. Some of these advanced imaging techniques are discussed below.

Magnetic Resonance Spectroscopic Imaging (MRSI or MRS)

(MRSI or MRS) is a non-invasive advanced MRI imaging technique that allows molecular information such as metabolite processing within the cells to be obtained about a cranial structure while the macroscopic organ is being imaged.

MRSI Uses:

The ability to distinguish necrotic tissue from recurrent tumor.
Presurgical and/or pre-Gamma Knife radiosurgical mapping of the somatosensory cortex in order to avoid critical structures in the brain during treatment.
The use of dynamic contrast MR imaging for the detection of angiogenesis (blood vessel formation in tumors) in gliomas and other neuro-oncologic disorders.
Enhanced interpretation of advanced CT angiographic, CT perfusion, and MR perfusion techniques to define areas of salvageable tissue in patients with cerebral ischemia (swelling).

The image formation contains metabolite peaks such as creatine, choline, myoinositol. When cases are presented at the Hoag Hospital Neurological Tumor Board, MRSI information is incorporated in the decision-making process and is used in optimizing patient treatment options.

For more information, e-mail us at GammaKnife@hoaghospital.org or call 866/446-2445

Functional Magnetic Resonance Imaging (f-MRI)

Hoag Hospital is the first hospital in OC to combine f-MRI imaging with GK radiosurgical treatment planning. (f-MRI) is a non-invasive imaging study that involves the measurement of dynamic blood oxygen level-dependent signal parameters within the brain. An f-MRI study measures a complex integral of vascular and metabolic components that vary over time and space as a function of tasks that the patient is asked to perform such as finger tapping or recitation of number sequences.

Standard patient MRI without functional brain mapping.
Patient f-MRI images during a finger tapping exercise allow for delineation of the areas of the brain that control motor functions (i.e. voluntary muscle movement).

f-MRI Uses:

Determine the exact location of critical nuclei in the temporal lobe responsible for speech, mathematical ability, muscle motor control, etc. Neurosurgeons use this information to quantify and limit the dose to these normal nerve cells that control normal daily activities.

For more information, e-mail us at GammaKnife@hoaghospital.org or call 866/446-2445

Magnetic Resonance Angiography (MRA)

MRA is a non-invasive diagnostic 3D imaging exam that is obtained in a state-of-the-art MRI scanner. The blood vessels of the brain and their internal flow rates are visualized and reconstructed in three dimensions. These images can show pathologies such as an arteriovenous malformation (AVM) which is a congenital vascular defect where an artery is connected directly to a vein without the intervening capillary network. Since an increased volume of blood is moving through the AVM, there is a resulting increase in the pressure on the draining vessels, which can cause hemorrhage and the formation of aneurysms – balloon-like formations – in the draining veins. An untreated AVM has a 3% chance per year of hemorrhage. The MRA images at Hoag Hospital are used for precise targeting of the nidus (center) of the AVM when the patient is treated on the Gamma Knife unit. The radiation delivered by the GK unit causes the nidus to dissolve over time.

Computed Tomography Angiography (CTA)

(CTA) is used at Hoag Hospital on the new ultrafast multislice CT scanner recently installed. CTA is a non-invasive 3D imaging study that allows for reconstructive imaging of the brain vasculature and the flow of blood through the vasculature. CTA, unlike MRA can provide more information about lesions that involve the bone or skull base region of the head. CTA scans are acquired in less time than MRA’s and are appropriate for patients who are unable to undergo MRA scanning due to pacemakers, metal implants or inability to fit in the MR scanner. Depending upon the location of the AVM, some patients are imaged with CTA, MRA and conventional 2D (two dimensional) angiography. This allows for highly customized treatment plans in cases where the nidus of the AVM is difficult to visualize.

Stereotactic Localization Technique

The use of three-dimensional technology to perform a biopsy in the brain is currently practiced using Hoag’s Brain Lab stereotactic biopsy system. This system enables the neurosurgeon to three dimensionally precisely determine the biopsy incision location.

Positron Emission Tomography (PET)

Positron Emission Tomography or PET is an imaging technique that visualizes the physiology of human anatomy using a positron emitting radiopharmaceutical. Unlike CT scanning, which looks primarily at structure and shape, PET evaluates changes in chemistry, function and metabolism of brain tissues. In the neurosciences (Gamma Knife), PET is used to determine tumor response to radiation or chemotherapy treatments, to locate growing tumors, to aid in diagnosing recurrence after treatment, and to help differentiate new tumor growth from radiation necrosis.

For more information, e-mail us at GammaKnife@hoaghospital.org or call 866/446-2445

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