Accuracy of Renal MRA Techniques in Literature

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Table 1 shows sensitivity and specificity data reported for diagnosing renal artery stenosis using non-contrast MR angiography. Many of the limitations due to flow and saturation artifacts on flow-based techniques are eliminated by using gadolinium contrast to enhance the renal MRA examina tion. Gadolinium contrast agents enormously increase the SNR allowing for higher resolution in short scan times. Using conventional angiography as a reference standard, the reported sensitivity and specificity of renal MRA with gadolinium enhancement for diagnosing renal artery stenosis are 88-100% and 70-100% respectively (Table 2) with similar interobserver variability [25], especially for severe stenoses greater than 70%. Accuracy can be improved by evaluation of the vessel area on mul-tiplanar reformats. This requires high-resolution renal 3D CE MRA with parallel imaging. MRA thus avoids invasive diagnostic procedures [26]. In addition, renal MRA eliminates the need for aortog-raphy at the time of subsequent angioplasty [27] and thereby dramatically reduces iodinated contrast load and radiation exposure during renal revascularization. By showing the precise location of each renal artery and the angle arising from the aorta, catheter manipulation during renal revascu-larization may be minimized, thereby potentially reducing the procedural risk of cholesterol emboli.

A recent meta-analysis compared MRA, CTA, ultrasound, captopril renography and captopril test for diagnosing renal artery stenosis [28]. Gadolinium-enhanced MRA and CTA with iodi-nated contrast were found to be highly and comparably accurate with a 0.99 area under the receiver-operator curve (ROC). Ultrasound, time-offlight MRA, and captopril renography were significantly less accurate. Compared to CE MRA, ultrasound is more operator-dependent with inferior sensitivity; renal scintigraphy is also significantly less accurate, especially in patients with impaired renal function; CTA is as accurate as MRA, but us

Table 2. Sensitivity and specificity of contrast- enhanced renal MRA

Technique

Author

# Patients

Sensitivity (%)

Specificity (%)

3D Gd

Prince [60]

19

100

93

3D Gd

Grist [61]

35

89

95

3D Gd

Snidow [62]

47

100

89

3D Gd

Holland [63]

63

100

100

3D Gd

Steffens [64]

50

96

95

3D Gd

Rieumont [65]

30

100

71

3D Gd

De Cobelli [66]

55

100

97

3D Gd

Bakker [67]

50

97

92

3D Gd

Hany [68]

103

93

90

3D Gd

Thornton [69]

62

88

98

3D Gd

Schoenberg [70]

26

94-100

96-100

3D Gd

Thornton [71]

42

100

98

3D Gd + PC

Cambria [72]

25

97

100

3D Gd

Ghantous [73]

12

-

100

3D Gd

Gilfeather [25]

54

Overestimate 21%, underestimate 14%

SD: MRA = 6.9'

%, Angio = 7.5%

3D Gd

Marchand [74]

88-100

71-100

3D Gd

Shetty [39]

51

96

92

3D Gd

Winterer[75]

23

100

98

3D blood pool

Weishaupt [76]

20

82

98

3D Gd

Bongers [77]

43

100

94

Time-resolved

Volk [78]

40

93

83

3D Gd at 1T

Oberholzer [79]

23

96

97

3D Gd

Korst [80]

38

100

85

3D Gd

De Corbelli [81]

45

94

93

3D Gd

Mittal [15]

26

96

93

3D Gd

Voiculescu [82]

36

96

86

3D Gd

Qanadli [3]

41

97

64

3D Gd

Hood [83]

21

100

74

3D Gd + cine PC

Schoenberg [38]

23

97% agreement with DSA

Time-resolved

Krause [14]

71

75

95.7

3D Gd

Willmann [84]

46

92-93

99-100

3D Gd

Coenegrachts [85]

25

100

98

es ionizing radiation as well as nephrotoxic contrast material, which are considered less favorable, particularly in patients at risk for renal insufficiency. However, CTA may be preferred when there are contraindications to MR such as a pacemaker, orbital metal fragment, severe claustrophobia or brain aneurysm clip.

In addition to diagnosing renal artery stenosis, 3D CE MRA identifies concomitant vascular conditions including aorto-iliac occlusive disease, ulcerated atherosclerotic plaques, the angle of the renal artery with respect to the aorta, early renal artery branching and accessory renal arteries which may influence planning for interventional procedures. Furthermore, MRA can be combined with additional pulse sequences that enable assessment of kidney function and hemodynamic significance of borderline renal artery stenosis.

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