Black-blood MR angiography with GRASE: measurement of flow-induced signal attenuation

T2 dark blood MRA for renal artery stenosis detection: preliminary observations

OBJECTIVE

This study evaluated the ability of a fast spin echo T2 weighted dark blood sequence to characterize significant (>50%) renal artery stenosis compared to conventional angiography.

METHODS

Sixteen patients underwent conventional catheter angiography for either renal artery stenosis evaluation or as potential renal donors. Each patient then had an MR study of the renal arteries and kidneys with fast spin echo T2 weighted MR (TR 4000, TE 102, 8 echo train length) on a Superconducting 1.5T Magnet. Results were compared with angiography and inter and intra observer statistics were calculated.

RESULTS

A total of 36 renal arteries were imaged in 32 kidneys with 12 stenoses >50%. Fast spin echo T2 weighted MR is 94% accurate (95%CI: 87-100%) in detection of significant renal artery stenosis. Dark blood MRA (DBMRA) is 96% sensitive (95%CI: 89-100), 92% specific, with a predictive value positive of 96% for classifying real arteries as normal or significantly stenosed. Inter and intra observer statistics demonstrate good to excellent agreement in renal artery classification (kappa>0.60).

CONCLUSION

DBMRA may be a useful adjunct to renal MR evaluation in hypertension.

SUMMARY

A total of 36 renal arteries were imaged in 32 kidneys with 12 stenoses >50%. Fast spin echo T2 weighted MR is 94% accurate (95%CI: 87-100%) in detection of significant renal artery stenosis.

Multiple contrast fast spin-echo approach to black-blood intracranial MRA: use of complementary and supplementary information

Black-blood magnetic resonance angiography (black-blood MRA) could be considered an alternative to time-of-flight (TOF) MRA. In the cases of irregular flow conditions, it could be more advantageous than time-of-flight (TOF) MRA in providing vessel definition and delineation. Proton-density weighted (PDW) multi-slab three-dimensional fast spin-echo (3DFSE) sequences have been used to generate black-blood MRA. Unfortunately, multi-planar reformatted 3DFSE images often exhibit slab boundary artifacts (intensity variation in the slice direction) which create dark bands interfering with the identification of dark blood vessels. Furthermore, PDW measurements fail to darken slow flowing or re-circulating blood in some circumstances. In this work, a dual-contrast multi-slab 3DFSE acquisition is used to approach black-blood MRA. This sequence simultaneously provides proton-density weighted (PDW) and T(2)-weighted (T2W) images which can be further integrated together to produce black-blood angiograms gained by utilizing complementary contrast and supplementary vascular information. Additionally, a technique of suppressing slab boundary artifact has been incorporated into this sequence. This approach provides: i) good SNR measurement of anatomy for the PDW image and optimal black-blood angiograms from the T2W image; ii) scan time efficiency (dual-contrast image sets plus black-blood angiograms within one acquisition); and iii) suppressed slab boundary artifacts as well as minimized mis-registration error.

A median filter for 3D FAST spin echo black blood images of cerebral vessels

High-resolution black-blood MRA images of intracranial vascular anatomy can be obtained using 3D fast spin-echo techniques. Although these images demonstrate excellent contrast between vessels and surrounding soft tissues, the dark signal from air and bone can obscure the desired vascular information when a minimum intensity projection image is created. In this paper, we describe an image processing technique based upon a median filter that is effective for detecting narrow vessel-like structures. Minimum intensity projection images of the filtered MRA volume can be obtained in any orientation without prior segmentation of the skull or surrounding air spaces. The filter is very effective for detecting and visualizing small vessels, but is much less effective for detecting vessels and vascular pathology larger than the filter detection width. The filtering technique is demonstrated on black-blood MRA images from a volunteer study.