01) Technique and Indications

Some CT and MR techniques require a good contrast bolus (CTA, CT perfusion, MR perfusion)

Q: What arm should be used for injection?

A: The right arm. The left arm is prone to restriction from tortuosity of arch vessels.

Reference:

http://www.ajronline.org/doi/pdfplus/10.2214/ajr.170.6.9609192

Imaging/Computer Graphics

Q: What is a voxel?

A: In cross sectional imaging, it is the “volume element” of anatomy that is represented in an image by a pixel.

Q: What is an isotropic voxel?

A: It is a voxel with equal dimensions. Source images made from isotropic voxels are used to create multiplanar refromatted images that have resolution independent of plane angulation.

Q: What is a pixel?

A: It is the the basic subunit of a digital image, a “picture element”. In imaging it represents the attenuation/signal of a corresponding unit of anatomy or “voxel” For CT and MR pixel size can be calculated:

pixel size(mm)=FOV(mm)/matrix (is in the dicom header 0028,0010 and 0028,0011)

FOV=field of view (field of view is in the DICOM header 0018,1100)

e.g. a 25cm field of view and a 256X256 matrix would produce an image with a pixel representing about 1 square mm of anatomy. The voxel volume could be determined if you knew what?

A: slice thickness, e.g. 5mm.

Q: What is a typical voxel dimension for a brain MR?

A: assuming the factors above are typical 1x1x5 mm is a good approximation.