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Orientation
If available, some graphic aids can be helpful to show image orientations.
1) A graphic icon of the labeled primary axes (A, L, H) with relative lengths given by direction sines and system of coordinates as if viewed from the normal to the image plane can help orient the viewer, both to identify image plane orientation and to indicate possible in plane rotation.
2) In graphic prescription of obliques from other images, a sample original image with an overlaid line or set of lines indicating the intersection of the original and oblique image planes can help orient the viewer.
The 3 basic orthogonal slice orientations are:
transverse (T), sagittal (S) and coronal (C).
The basic anatomical directions are:
right(R) to left (L), posterior (P) to anterior (A), and feet (F) to head (H).
A standard display orientation for images in the basic slice orientation is:
1) transverse: A to top of image and L to right,
2) coronal: H to top of image and L to right and
3) sagittal: H to top of image and A to left.
The location in the R/L and P/A directions can be specified relative to the axis of the scanner.
The F/H location can be specified relative to a convenient patient structure.
The orientation of single oblique slices can be specified by rotating a slice in one of the basic orientations toward one of the other two basic orthogonal planes about an axis defined by the intersection of the 2 planes.
Double oblique slices can be specified as the result of tipping a single oblique plane toward the remaining basic orientation plane, about an axis defined by the intersection of the oblique plane and the remaining basic plane. In double oblique angulations, the first rotation is chosen about the vertical image axis and the second about the (new) horizontal axis. Angles are chosen to have magnitudes less than 90° (for single oblique slices less than 45°); the sign of the angle is taken to be positive when the rotation brings positive axes closer together.
Boltzmann Distribution
When a group of spins is placed in a magnetic field, each spin aligns in one of the two possible orientations. The relative numbers of spins with different alignments will be given by the Boltzmann distribution.
Definition: if a system of particles, which are able to exchange energy in collisions is in thermal equilibrium, then the relative number (population) of particles, N1 and N2, in two particular energy levels with corresponding energies, E1 and E2, is given by N1/N2 = exp [-(E1 - E2)/kT ] where k is the Boltzmann constant and T is the absolute temperature. For example, in NMR of protons at room temperature in a magnetic field of 0.25 tesla, the difference in relative numbers of spins aligned with the magnetic field and against the field is about one part in a million; the small excess of nuclei in the lower energy state is the basis of the net magnetization and the resonance phenomenon.
Digital Radiography
(DR) Digital radiography uses a special electronic x-ray detector, which converts the radiographic image into a digital picture for review on a computer monitor. The digital image is then stored and can be post processed by changing the magnification, orientation, brightness, and contrast. Digital radiography (also called direct radiography) is a progressive development of computed radiography (CR).
These advantages can lead to fewer 'recalls' (repeated x-ray images) including a lower radiation dose than analog or conventional radiography. DR and CR systems use no chemicals to process the x-ray images and the hazardous materials and waste associated with film development are eliminated.

Advantages of digital radiography compared with conventional radiography:
saves time and costs due to more effective imaging process and workflow;
improved diagnostic quality images also in cases of x-ray under exposition or over exposition;
lower repeat rate;
films and developing chemicals are omitted;
reduction of hazardous chemical waste.
Oblique
A plane or section not perpendicular to the xyz coordinate system, such as long and short axis views of the heart.

See also Orientation, Mediolateral-Oblique View, Lateral View, Lateromedial, Breast Imaging, and Stack.
Stack
A collection of slices with the same orientation. Multi-stack acquisitions are possible when the stack parameter is greater than one, for example in lumbar spine CT exams with individual angulation (oblique) for every disc.
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 [last update: 2023-11-06 02:01:00]