(PS) Excitation technique applying repeated RF pulses in times comparable to or shorter than T1. Incomplete T1 relaxation leads to reduction of the signal amplitude; there is the possibility of generating images with increased contrast between regions with different relaxation times.
Although partial saturation is also commonly referred to as saturation recovery, that term should properly be reserved for the particular case of partial saturation in which recovery after each excitation effectively takes place from true saturation. A GRE sequence where α = 90° is identical to the partial saturation or saturation recovery pulse sequence.
It does not directly produce images of T1. However, since the measured signal will depend on T1, the method generates contrast between regions with different relaxation times. If T2 and/or T2 effects are minimized through the use of a short echo time TE, the result is a T1 weighted image. It is not a T1 image due to the possible presence of spin density and T2 effects as well as the nonlinear dependence on T1.
The change in signal from a region resulting from a change in the interpulse time, TR, can be used to calculate T1 for the region.

The partial volume effect is the loss of contrast between two adjacent tissues in an image caused by insufficient resolution so that more than one tissue type occupies the same voxel (or pixel). That may induce a partial volume artifact, dependent on the size of the image voxel. If fat and water spins occupy the same voxel, their signals interfere destructively. A small amount of water signal may be eliminated by a larger lipid signal from the same voxel, resulting in a voxel that appears to contain only lipid. The partial volume effect is minimal with thin slice thickness and sufficiently high resolution, so that fat and water or other different structures are unlikely to occupy the same voxel.

Take thinner slices, and higher resolution (smaller voxel), but remain this may result in poorer signal to noise ratio in the image.

(PACS) A system used to communicate and archive medical imaging data, mostly images and associated textural data generated in a radiology department, and disseminated throughout the hospital. A PACS is usually based on the DICOM (Digital Imaging and Communications in Medicine) standard.
The main components in the PACS are:
Acquisition devices, which acquire their data in direct digital format, like a MRI system, are most easily integrated into a PACS.
Short term archives need to have rapid access, such as provided by a RAID (redundant array of independent disks), whereas long term archives need not have such rapid access and can be consigned, e.g. to optical disks or a magnetic.
High speed networks are necessary for rapid transmission of imaging data from the short term archive to the diagnostic workstations. Optical fiber, ATM (asynchronous transfer mode), fast or switched Ethernet, are examples of high speed transmission networks, whereas demographic textural data may be transmitted along conventional Ethernet.
Sophisticated software is a major element in any hospital-wide PACS. The software concepts include: preloading or prefetching of historical images pertinent to current examinations, worklists and folders to subdivide the vast mass of data acquired in a PACS in a form, which is easy and practical to access, default display protocols whereby images are automatically displayed on workstation monitors in a prearranged clinically logical order and format, and protocols radiologists can rapidly report worklists of undictated examinations, using a minimum of computer manipulation.

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(THK) The thickness of an imaging slice. As the slice profile may not be sharp edged, a criterion such as the distance between the points at half the sensitivity of the maximum (FWHM) or the equivalent rectangular width (the width of a rectangular slice profile with the same maximum height and same area) is used to determine thickness.

For the image quality its important to choose the best fitting slice thickness for an examination. When a small item is entirely contained within the slice thickness with other tissue of differing signal intensity then the resulting signal displayed on the image is a combination of these two intensities. If the slice is the same thickness or thinner than the small structure, only that structures signal intensity is displayed on the image. This partial volume averaging effect explains the vanishing of fine details by choosing slices too large for the scanned object.

See also Partial Volume Artifact.