System

Neuroimaging

Axial Head CT

Head CTs are performed by acquiring discrete, axial slices through the brain, ranging in thickness from 2-5mm/slice. In some cases, the CT data is acquired as a helix of density data which is then reformatted into the axial, coronal, or sagittal planes.

Head CTs can be performed without iv contrast (unenhanced), or following iv contrast injection (enhanced), depending on what the clinical situation is. On enhanced scans, the arteries, veins, dura and meninges all become brighter since they take up the contrast. The blood brain barrier prevents the contrast from being taken up by the brain parenchyma, so it does not become brighter.

This is an enhanced CT of the brain after intravenous contrast was administered.

Axial PD-weighted MRI

MRIs are acquired as thin slices in the axial, coronal, or sagittal planes. PD (proton density) weighting is a technique used to acquire the images that results in a standard, specific appearance of normal tissues. On PD images of the brain, fluid appears light gray, and can be hard to differentiate from gray matter. Gray matter is also light gray, and white matter is darker gray. On PD images, the contrast between white and gray matter is excellent. Most vessels are black. The subcutaneous fat is white.

image-overlay-PD-weight-MRI-1 — PD-weighted MRI (1)

Axial T2-weighted MRI

MRIs are acquired as thin slices in the axial, coronal, or sagittal plane. T2 weighting describes the technique used to acquire images in a particular way that causes fluid to look bright (white). Gray matter appears mid to light gray, and white matter is darker than gray matter. Most vessels are black. The subcutaneous fat is sometimes white, and sometimes dark, such as if a technique called ‘fat saturation’ has been employed.

Sagittal T1-weighted MRI

MRIs are obtained as thin slices in the axial, coronal, or sagittal planes. T1 weighting is a technique used to acquire images in which fluid appears dark/black. Gray matter appears dark gray, and white matter is lighter than gray matter. The appearance of blood vessels is variable. In the series that follows, the large vessels, like the carotid arteries and circle of Willis arteries are white. The subcutaneous fat is white.

image-overlay-sagittal-T1-MRI-brain-1 — Sagittal T1-Weighted MRI (1)

Coronal T2-weighted MRI

MRIs are acquired as thin slices in the axial, coronal, or sagittal plane. T2 weighting describes the technique used to acquire images in a particular way that causes fluid to look bright (white). Gray matter appears mid to light gray, and white matter is darker than gray matter. Most vessels are black. The subcutaneous fat is sometimes white, and sometimes dark, like when a technique called ‘fat saturation’ has been employed, as is the case in the series of coronal images which follows.

image-overlay-coronal-T2-MRI-brain-1 — Coronal T2-Weighted MRI (1)

Conventional Cerebral Angiography

Aortic Arch

These images were aquired by rapid injection of iodinated contrast material through a catheter placed into the ascending aorta, with rapid sequential radiographs obtained.

The image is aquired in a left anterior oblique projection, which optimizes viewing of the arch and great vessels origins. On this image, the bones are included. On the subsequent images, the bones have been 'subtracted', which increases the conspicuity of the opacified vessels.

image-overlay-aortic-arch-early — Aortic Arch Angiogram (early image). Only the proximal aspects of the vessels are opacified well on this early image.

Internal Carotid (AP)

cerebral-angio-ap-1 — Internal Carotid Angiogram (bones included)

These images were aquired by rapid injection of iodinated contrast material through a catheter placed into the right internal carotid artery, with rapid sequential radiographs obtained.

The image is aquired in an antero-posterior (AP) projection, which optimizes viewing of the internal carotid artery bifurcation. The cavernous segment of the carotid artery is superimposed, and the bifurcation of the middle cerebral artery is not well visualized in this projection.

On this image, the bones are included. On the subsequent images, the bones have been 'subtracted', which increases the conspicuity of the opacified vessels. Only the proximal aspects of the vessels are opacified well on this early image.

image-overlay-internal-carotid-early — Interal Carotid Angiogram (AP, early image). Only the proximal aspects of the vessels are opacified well on this early image.

Carotid Angiogram Venous Phase

The injected contrast has now passed through the arterial circulation and into the venous circulation, opacifying small cortical veins and the dural venous sinuses.

image-overlay-internal-carotid-venous — Interal Carotid Angiogram (AP, venous phase)

Internal Carotid (Lateral)

cerebral-angio-lateral-1 — Internal Carotid Artery (bones included)

These images were aquired by rapid injection of iodinated contrast material through a catheter placed into the right internal carotid artery, with rapid sequential radiographs obtained.

The image is aquired in a lateral projection, which optimizes viewing of the cavernous segment of the internal carotid artery. The course of the anterior cerebral artery is seen, parallelling the corpus callosum. The bifurcation of the internal carotid artery and middle cerebral artery are not well visualized in this projection.

On this image, the bones are included. On the subsequent images, the bones have been 'subtracted', which increases the conspicuity of the opacified vessels.

image-overlay-interal-carotid-angiogram-lateral-early — Interal Carotid Angiogram (lateral, early image). Only the proximal aspects of the vessels are opacified well on this early image. Note that the bones are subtracted out completely, only the vessles are opaque.

Venous Phase

The injected contrast has passed through the arterial circulation and into the venous system, opacifying the cortical and deep veins and dural venous sinuses. The field of view is small, and portions of the patient's skull are excluded from the image; thus the entirety of the superior sagittal sinus is not seen.

image-overlay-internal-carotid-angiogram-lateral-late-2 — Interal Carotid Angiogram (lateral, venous phase)

Vertebral Artery (AP)

The bones have been subtracted from this image. The contrast has been injected from a catheter placed into the right vertebral artery. Both the right and left vessels originating from the basilar artery will be opacified with either a right or left vertebral injection, and contrast often refluxes down the contralateral vertebral artery.

image-overlay-vertebral-angiogram-early — Vertebral Angiogram (AP, early image). The bones have been subtracted from this image. The contrast has been injected from a catheter placed into the right vertebral artery. Both the right and left vessels originating from the basilar artery will be opacified with either a right or left vertebral injection, and contrast often refluxes down the contralateral vertebral artery.

Venous Phase

Contrast has passed through the arterial circulation and into the veins, opacifying the dural venous sinuses draining the occipital lobes and cerebellum.

image-overlay-vertebral-angiogram-venous — Vertebral Angiogram (AP, venous phase)

Vertebral Artery (Lateral)

image-overlay-vertebral-angiogram-lateral-early — Vertebral Angiogram (lateral, early image). The bones have been subtracted from this image. The contrast has been injected from a catheter placed into the right vertebral artery. Both the right and left vessels originating from the basilar artery will be opacified with either a right or left vertebral injection.

Venous Phase

Contrast has passed through the arterial circulation and into the veins, opacifying the dural venous sinuses draining the occipital lobe and cerebellum. The right and left transverse and sigmoid sinues and internal jugular veins are opacified and overlap on the image.

image-overlay-vertebral-angiogram-lateral-venous — Vertebral Angiogram (lateral, venous phase).

Non-Invasive Cerebral Angiography

CT Angiography

CTA-circle-of-willis-reconstruction — CT Angiogram 3D reconstruction

These images were aquired with CT following rapid injection of iodinated contrast material through an arm vein. The scan was obtained while the contrast was located in the arterial circulation.

The data has been reformatted into a 3D image with a volume rendering technique. Only high density structures, like the contrast opacified vessels and the skull base, are displayed in this image. View the image as though the calvarium has been removed and you are looking down onto the skull base and circle of Willis.

CT Angiogram Anterior Circulation

This is a 3D volume rendered image of the anterior circulation, seen from an AP projection.

image-overlay-CTA-anterior-circulation — CTA Anterior Circulation

CT Angiogram Posterior Circulation

This is a 3D volume rendered image of the posterior circulation, seen from an AP projection.

image-overlay-CTA-posterior-circulation — CTA Posterior Circulation

MR Angiography

MR Angiography - Brain (AP)

MRA of the circle of Willis vessels can be performed without iv contrast enhancement. The technique capitalized on the properties of flowing blood. Vessels appear white on this type of image, and the background tissues are suppressed.

The images are reformatted to demonstrate the anterior and posterior circulation separately.

image-overlay-MRA-AP — MRA Anterior Circulation (AP)

MR Angiography - LAO projection

This image is obtained in the left anterior oblique (LAO) projection, which shows the cavernous segments of the internal carotid artery and the middle cerebral artery bifurcation better than the AP projection.

image-overlay-MRA-LAO — MRA Anterior Circulation (LAO)

MR Angiography - RAO projection

This image is obtained in the right anterior oblique (RAO) projection. By viewing both the LAO and RAO projections, the bifurcations of the middle cerebral and internal carotid arteries can be accurately evaluated on both the right and left sides.

image-overlay-MRA-RAO — MRA Anterior Circulation (RAO)

MR Angiography - Posterior Circulation (AP)

This image shows only the posterior circulation. The anterior circulation has been removed from the data displayed.

image-overlay-MRA-post-cir — MRA Posterior Circulation (AP)

MR Angiography - Posterior Circulation (Lateral)

This image shows only the posterior circulation. Since the vertebral arteries and branches of the basilar artery are superimposed, the right and left cannot be distinguished.

image-overlay-MRA-post-cir-lat — MRA Posterior Circulation (lateral)

Circle of Willis: MR and CT Angiograms

Both of the images shown are reformatted images from an CT angiogram and MR angiogram of the head. Both are viewed from a superior aspect; as though the brain has been removed and you are looking at the circle of willis from above. The anterior cranial fossa is at the top of the image, and the foramen magnum would be at the bottom of the image. Notice the anatomy seen with each is slightly different; on the MRA, the entire course of the internal carotid arteries is visible, while on the CTA, it is partially obscured by the dense bone. Images are from two different patients.

image-overlay-Circle of Willis: MRA — Circle of Willis: MRA

MR Venography

MR Venography (AP)

These images are created without using IV contrast. The technique used capitalizes on the magnetic properties of flowing blood, which appears white on the image. The background tissues are suppressed.

image-overlay-MRV-ap-projection — MRV AP Projection

MR Venography (Lateral)

Structures on the right and left sides of the head are superimposed on this image. Intravenous contrast is not needed for this technique.

image-overlay-MRV-lateral-projection — MRV Lateral Projection