Multiple inversion recovery reduces static tissue signal in angiograms

Abstract

Spin label angiography compares two images by subtraction. The first is obtained after blood in one region is labeled by inversion and flows into a region of interest. Labeling is not used for the second image, so only labeled blood remains in the final angiogram after subtraction. This subtraction is never perfect, but with starting images containing less static tissue signal, the remaining background can be reduced. This can be achieved by observing at the zero crossing following an inversion. Multiple inversions allow one to null the signal from tissues with differing T1 simultaneously. We present equations and sample calculations for inversion times and demonstrate the resistance to subject motions (peristalsis, breathing, speaking) resulting from two inversions. Adequate suppression of static tissue signal allows one to dispense with labeling and subtraction, halving the minimum time needed to acquire an image.

T1‐insensitive flow suppression using quadruple inversion‐recovery

“…Preparative multiple inversion RF pulses were used previously either for selective simultaneous zeroing of signals from two tissues with known T 1 (8,9) or for total suppression of a background signal from a variety of tissues (10,11). The first application is based on the double-inversion technique (8,9), whereas the second group of methods includes complex preparative sequences consisting of a 90°-pulse followed by two-, three-, or four inversion pulses (10,11). Unlike these techniques, in QIR the signal to be suppressed (i.e., from blood) is subjected only to the action of the inversion pulses, but it is not affected by an imaging part of the sequence or by additional 90°-pulses.…”

“…(10,11). This approach, however, is not suitable for the postcontrast blood suppression due to the wide variety of T 1 expected.…”

Relative changes of cerebral arterial and venous blood volumes during increased cerebral blood flow: Implications for BOLD fMRI

“…Multiple inversion recovery can be used to suppress tissue water signal based on the T 1 difference between blood and tissue (30). T 1 difference between blood and tissue can be enhanced by the introduction of relaxation or contrast agents into the blood (31).…”

“…In their study, albumin-bound Gd-DTPA was used to reduce the T 1 of blood water. By utilizing large T 1 differences between tissue and blood water, blood signal can be predominantly obtained by selective nulling of tissue water using double inversion methods (30,31). Since the characteristics of blood flow is invariant regardless of probing methods, e.g., 19 (31)).…”

Arterial spin labeling: its time is now

“…The successful approach of background suppression [7,8] is emphasized in the article of Maleki et al [9], where suppression is optimized and used to image blood flow to the eye. Since background suppression does reduce ASL signal by a significant factor, the community remains uncertain whether or how much background suppression to use.…”