T₁‐insensitive flow suppression using quadruple inversion‐recovery

Abstract

A new flow suppression method has been proposed for the acquisition of blood-suppressed (black-blood) images in combination with administration of a positive contrast agent. The technique employs the quadruple inversion-recovery (QIR) preparative pulse sequence, which consists of two double-inversion modules followed by two delays. Within each double inversion, a nonselective RF pulse is immediately followed by a slice-selective one. The time intervals of the sequence can be calculated using an algorithm based on minimization of the variation of a signal equation over an entire range of T 1 occurring in blood before and after contrast administration. QIR is highly insensitive to variations of Contrast-enhanced, blood-suppressed (black-blood) imaging of the vessel wall was recently proposed as a promising technique intended primarily for detection of neovasculature and inflammation in atherosclerotic plzzaque (1,2). In this challenging area, the black-blood contrast between the vessel wall and the lumen needs to be maintained despite considerable shortening of T 1 in blood after injection of a positive contrast agent. In addition, the quality of pre-and postcontrast images should allow for reliable measurement of contrast enhancement (CE) within different components of atherosclerotic plzzaque (1,2). The usefulness of postcontrast blood suppression was also demonstrated in brain imaging (3), where confusing venous enhancement and flow artifacts can be avoided. In the above applications (1-3), black-blood imaging was performed using the double inversion-recovery (DIR) method (4,5). Designed initially for inversion-based suppression of the signal from blood with normal physiological T 1 , DIR results in high-quality visualization of cardiovascular anatomy and is considered to be the most efficient black-blood imaging modality to date (6,7). However, the quality of blood suppression by DIR is highly sensitive to changes of T 1 in blood after contrast administration, because this method requires a precise knowledge of T 1 to calculate the proper inversion time (TI) (4,5). Usually, information about postcontrast T 1 of blood is unavailable in clinical contrast-enhanced imaging. Moreover, this parameter strongly depends on various factors, such as the properties and dosage of a contrast agent, the time between injection and data acquisition, the injection rate, and the physiological clearance of an individual patient. All of these factors make the postcontrast application of DIR uncertain, even if an initial guess about the expected T 1 can be made. Another limitation of DIR is related to the quantitative measurements of CE. To achieve good blood suppression, preand postcontrast DIR images should be obtained with different TI. At the same time, it may impose an instrumental bias in quantitative estimates due to partial saturation of stationary tissues produced by the DIR preparation. The resulting alterations of signal intensity have to be dependent on TI, especially in T 1 -weighted imaging with short repetition times...

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