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MR Flow Mapping in Coronary Artery Bypass Grafts: A Validation Study with Doppler Flow Measurements¹

¹ From the Depts of Cardiology (S.E.L., H.W.V., J.W.J., P.S., E.E.v.d.W.), Radiology (S.E.L., P.K., H.J.L., A.d.R.), and Medical Statistics (A.H.Z.), Leiden Univ Medical Center, Albinusdreef 2, 2333 ZA Leiden, the Netherlands; and the Interuniversity Cardiology Inst of the Netherlands, Utrecht (S.E.L, E.E.v.d.W., A.d.R.). Received Mar 2, 2001; revision requested Apr 11; revision received Jun 8; accepted Jul 5. S.E.L. supported by grant 97.173 from the Netherlands Heart Foundation. Address correspondence to A.d.R. (e-mail: a.de_roos@lumc.nl).

View larger version (52K): [in a new window]   Figure 1. Schematic representation of the small-diameter flow phantom used for turbo-field echo-planar MR flow mapping and intravascular Doppler flow measurements. The arrows indicate the direction of the flow. PVC = polyvinylchloride.

View larger version (27K): [in a new window]   Figure 2. Schematic representation of the breath-hold turbo-field echo-planar imaging (EPI) pulse sequence used for MR flow mapping. This sequence involves two excitations (two alpha pulses) within one heart phase interval, each of which are followed by three echo-planar imaging readouts. The repetition time (TR) of 11 msec is the time it takes to acquire three k lines after one alpha pulse, and the temporal resolution of 23 msec is the shot length (tshot) of six k lines (two x repetition time). Flow-sensitive and flow-compensated images were acquired in 10 shots and resulted in an imaging duration of 20 heartbeats.

View larger version (36K): [in a new window]   Figure 3. The plot graphs show the correlation of APV (cm/sec) (A) and DPV (cm/sec) (B) with MR flow mapping and the Doppler flow wire in the flow phantom. The limits of agreement between noninvasively and invasively measured peak velocity values are depicted in the Bland-Altman plots (C, D). Dashed horizontal lines in C and D show the mean difference between MR flow mapping and the Doppler flow wire plus or minus 2 SDs.

View larger version (145K): [in a new window]   Figure 4a. A typical example of MR studies (a-c) and cardiac catheterization (d, e) in a patient with nonstenotic sequential vein graft to the circumflex coronary artery. a, MR angiogram of the graft shows a maximal intensity projection. The plane of the flow image perpendicular to the course of the graft is indicated by an asterisk. Ao = aorta, PA = pulmonary artery, SCV = superior caval vein. The modulus and phase-flow image in middiastole (b) and the resulting baseline and stress velocity curves (c) are depicted. Morphologic and functional information of the same grafts was also obtained during cardiac catheterization by using standardized coronary angiographic techniques (d) and the intravascular Doppler flow wire (e), respectively. Both flow techniques revealed the typical biphasic velocity pattern, with main velocity during diastole. APV and DPV increased during stress.

View larger version (142K): [in a new window]   Figure 4b. A typical example of MR studies (a-c) and cardiac catheterization (d, e) in a patient with nonstenotic sequential vein graft to the circumflex coronary artery. a, MR angiogram of the graft shows a maximal intensity projection. The plane of the flow image perpendicular to the course of the graft is indicated by an asterisk. Ao = aorta, PA = pulmonary artery, SCV = superior caval vein. The modulus and phase-flow image in middiastole (b) and the resulting baseline and stress velocity curves (c) are depicted. Morphologic and functional information of the same grafts was also obtained during cardiac catheterization by using standardized coronary angiographic techniques (d) and the intravascular Doppler flow wire (e), respectively. Both flow techniques revealed the typical biphasic velocity pattern, with main velocity during diastole. APV and DPV increased during stress.

View larger version (24K): [in a new window]   Figure 4c. A typical example of MR studies (a-c) and cardiac catheterization (d, e) in a patient with nonstenotic sequential vein graft to the circumflex coronary artery. a, MR angiogram of the graft shows a maximal intensity projection. The plane of the flow image perpendicular to the course of the graft is indicated by an asterisk. Ao = aorta, PA = pulmonary artery, SCV = superior caval vein. The modulus and phase-flow image in middiastole (b) and the resulting baseline and stress velocity curves (c) are depicted. Morphologic and functional information of the same grafts was also obtained during cardiac catheterization by using standardized coronary angiographic techniques (d) and the intravascular Doppler flow wire (e), respectively. Both flow techniques revealed the typical biphasic velocity pattern, with main velocity during diastole. APV and DPV increased during stress.

View larger version (168K): [in a new window]   Figure 4d. A typical example of MR studies (a-c) and cardiac catheterization (d, e) in a patient with nonstenotic sequential vein graft to the circumflex coronary artery. a, MR angiogram of the graft shows a maximal intensity projection. The plane of the flow image perpendicular to the course of the graft is indicated by an asterisk. Ao = aorta, PA = pulmonary artery, SCV = superior caval vein. The modulus and phase-flow image in middiastole (b) and the resulting baseline and stress velocity curves (c) are depicted. Morphologic and functional information of the same grafts was also obtained during cardiac catheterization by using standardized coronary angiographic techniques (d) and the intravascular Doppler flow wire (e), respectively. Both flow techniques revealed the typical biphasic velocity pattern, with main velocity during diastole. APV and DPV increased during stress.

View larger version (91K): [in a new window]   Figure 4e. A typical example of MR studies (a-c) and cardiac catheterization (d, e) in a patient with nonstenotic sequential vein graft to the circumflex coronary artery. a, MR angiogram of the graft shows a maximal intensity projection. The plane of the flow image perpendicular to the course of the graft is indicated by an asterisk. Ao = aorta, PA = pulmonary artery, SCV = superior caval vein. The modulus and phase-flow image in middiastole (b) and the resulting baseline and stress velocity curves (c) are depicted. Morphologic and functional information of the same grafts was also obtained during cardiac catheterization by using standardized coronary angiographic techniques (d) and the intravascular Doppler flow wire (e), respectively. Both flow techniques revealed the typical biphasic velocity pattern, with main velocity during diastole. APV and DPV increased during stress.

View larger version (23K): [in a new window]   Figure 5a. Correlation between (a) APV (cm/sec), (b) DPV (cm/sec), and (c) velocity reserve (CFR) measured with MR flow mapping and the Doppler flow wire. = grafts with luminal stenosis of less than 50% (nonstenotic), = grafts with luminal stenosis greater than or equal to 50% stenosis (stenotic) in either the graft or coronary segments beyond the distal graft anastomosis. Similar linear regression lines were found in nonstenotic (thin line) and stenotic grafts (thick line). Ln = logarithmic transformation.

View larger version (22K): [in a new window]   Figure 5b. Correlation between (a) APV (cm/sec), (b) DPV (cm/sec), and (c) velocity reserve (CFR) measured with MR flow mapping and the Doppler flow wire. = grafts with luminal stenosis of less than 50% (nonstenotic), = grafts with luminal stenosis greater than or equal to 50% stenosis (stenotic) in either the graft or coronary segments beyond the distal graft anastomosis. Similar linear regression lines were found in nonstenotic (thin line) and stenotic grafts (thick line). Ln = logarithmic transformation.

View larger version (20K): [in a new window]   Figure 5c. Correlation between (a) APV (cm/sec), (b) DPV (cm/sec), and (c) velocity reserve (CFR) measured with MR flow mapping and the Doppler flow wire. = grafts with luminal stenosis of less than 50% (nonstenotic), = grafts with luminal stenosis greater than or equal to 50% stenosis (stenotic) in either the graft or coronary segments beyond the distal graft anastomosis. Similar linear regression lines were found in nonstenotic (thin line) and stenotic grafts (thick line). Ln = logarithmic transformation.

View larger version (22K): [in a new window]   Figure 6. Bland-Altman plot graph shows the limits of agreement between noninvasively and invasively measured APV (cm/sec) with MR flow mapping and the intravascular Doppler flow wire, respectively. Dashed horizontal lines show the mean difference between MR and Doppler measurements after log transformation plus or minus 2 Sds. Ln = logarithmic transformation.