Quick Overview
Please note that there are different common names for this artifact.

Black boundary artifacts are black lines following voxels where both water and fat protons are present in the same voxel. This artifact arise along the boundary of organs or tissues perpendicular to the frequency encoding direction, and occurs preferentially in gradient echo sequences with out of phase echo times.

Fat suppression techniques eliminate this artifact. For artifact reducing helps a smaller water fat shift (high bandwidth), a higher matrix or/and an in phase TE.

See also Chemical Shift Artifact.

Quick Overview
Please note that there are different common names for this artifact.

During frequency encoding, fat protons precess slower than water protons in the same slice because of their magnetic shielding. Through the difference in resonance frequency between water and fat, protons at the same location are misregistrated (dislocated) by the Fourier transformation, when converting MRI signals from frequency to spatial domain. This chemical shift misregistration cause accentuation of any fat-water interfaces along the frequency axis and may be mistaken for pathology. Where fat and water are in the same location, this artifact can be seen as a bright or dark band at the edge of the anatomy.
Protons in fat and water molecules are separated by a chemical shift of about 3.5 ppm. The actual shift in Hertz (Hz) depends on the magnetic field strength of the magnet being used. Higher field strength increases the misregistration, while in contrast a higher gradient strength has a positive effect. For a 0.3 T system operating at 12.8 MHz the shift will be 44.8 Hz compared with a 223.6 Hz shift for a 1.5 T system operating at 63.9 MHz.

For artifact reduction helps a smaller water fat shift (higher bandwidth), a higher matrix, an in phase TE or a spin echo technique. Since the misregistration offset is present in the read out axis the patient may be rescanned with this axis parallel to the fat-water interface. Steeper gradient may be employed to reduce the chemical shift offset in mm. Another strategy is to employ specialized pulse sequences such as fat saturation or inversion recovery imaging. Fat suppression techniques eliminate chemical shift artifacts caused by the lack of fat signal.

See also Black Boundary Artifact and Magnetic Resonance Spectroscopy.

(DIR or DIRT1) Double inversion recovery T1 measurement is a T1 weighted black blood MRA sequence in which the signal from blood is suppressed. The inversion time to suppress blood is described as the duration between the initial inversion pulse and time point that the longitudinal magnetization of blood reaches the zero point. The readout starts at the blood suppression inversion time (BSP TI) and blood in the imaging slice gives no signal. This inversion time is around 650 ms with a 60 beat per minute heart rate at 1.5 T.
The TI can be decreased by using a wider receive bandwidth, shorter echo train length and/or narrow trigger window. Wide bandwidth also decreases the blurring caused by long echo trains at the expense of signal to noise ratio. In case of in plane or slow flow the suppression of the signal from blood may be incomplete. With increased TE or change of the image plane the blood suppression can be improved.
Double inversion recovery is a breath hold technique with one image per acquisition used in cardiovascular imaging. The patient is instructed to hold the breath in expiration (if not possible also inspiration can be taken), so that the end diastolic volume in the cardiac chambers would be the same during entire scanning. DIR provides fine details of the boundary between the lumen and the wall of the cardiac chambers and main vascular and heart structures, pericardium, and mediastinal tissues.

Dwell Time is the primary determinant of noise in the MR image, the time between samplings (sampling interval). Noise is proportional to the square root of the bandwidth and the bandwidth is inversely proportional to the dwell time. A longer dwell time means a lower noise thus a greater signal to noise ratio. This also lengthens the total echo sampling time (longer TE).

[This entry is marked for removal.]

(July 20, 2009 - EPIX Pharmaceuticals, Inc. announced today that, in light of the company's lack of capital and inability to obtain additional financing or consummate a strategic transaction, it has entered into an Assignment for the Benefit of Creditors, effective immediately, in accordance with Massachusetts law).
EPIX has been a specialty pharmaceutical firm developing targeted contrast agents to improve the capability of MRI as a diagnostic tool for a variety of diseases. Gadofosveset trisodium (formerly MS-325, Vasovist™, now ABLAVARt™), is an injectable intravascular contrast agents designed for multiple vascular imaging applications, including peripheral vascular disease and coronary artery disease. EPIX conducted a pivotal Phase III trial for the detection of peripheral vascular disease, as well as a Phase II feasibility trial for coronary artery disease diagnosis.
To ensure rapid development and adoption of gadofosveset trisodium into clinical practice upon regulatory approval, EPIX pursued an aggressive product development plan and commercialization strategy. The Company established an exclusive, worldwide sales and marketing agreement with Bayer Schering Pharma AG. EPIX also established corporate collaborations with GE Healthcare, Philips Medical Systems and Siemens Medical Systems, the three leading MRI manufacturers, which together account for approximately 80 percent of the MRI machines installed worldwide.
EPIX had other MRI contrast agents under development, most significantly a novel prototype blood clot agent (EP-2104R). Potential clinical applications for this type of agent include detection of deep venous thrombosis, pulmonary embolism and blood clots in the coronary and carotid arteries. Currently, there is no high resolution imaging technique to directly visualize blood clots in patients with suspected cardiovascular disease.