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Left-to-Right Cardiac Shunts: Comparison of Measurements Obtained with MR Velocity Mapping and with Radionuclide Angiography¹

¹ From the Departments of Clinical Physiology (H.A., O.P.), Radiology (C.H., S.L., F.S.), Cardiology (U.T.), and Pediatric Medicine (K.H., G.B.), Lund University Hospital, S-221 85 Lund, Sweden. Received June 2, 1998; revision requested July 22; revision received September 18; accepted November 19. Supported in part by the Swedish Medical Research Council, Stockholm, Sweden; Hellmuth Herz Foundation, Lund, Sweden; Swedish Royal Physiographic Society, Lund, Sweden; and Swedish Heart Lung Foundation, Stockholm, Sweden. Address reprint requests to H.A.

View larger version (162K): [in a new window]   Figure 1a. MR images demonstrate the planes (lines) used to measure blood flow. (a) Coronal spin-echo image (942/30, section thickness of 6 mm, field of view of 380 mm, and matrix of 172 x 256) of the ascending aorta, with the plane used for velocity mapping indicated. (b) Sagittal breath-hold turbo spin-echo image (2,033/85, section thickness of 8 mm, field of view of 400 mm, and matrix of 230 x 512) obtained along the pulmonary trunk. (c) From b, a coronal oblique plane (indicated in b) was used to obtain another breath-hold turbo spin-echo image with the patient in the prone position (1,857/85, section thickness of 8 mm, field of view of 450 mm, and matrix of 276 x 512). Flow was measured in the pulmonary trunk just above the pulmonary valves (velocity mapping plane indicated).

View larger version (189K): [in a new window]   Figure 1b. MR images demonstrate the planes (lines) used to measure blood flow. (a) Coronal spin-echo image (942/30, section thickness of 6 mm, field of view of 380 mm, and matrix of 172 x 256) of the ascending aorta, with the plane used for velocity mapping indicated. (b) Sagittal breath-hold turbo spin-echo image (2,033/85, section thickness of 8 mm, field of view of 400 mm, and matrix of 230 x 512) obtained along the pulmonary trunk. (c) From b, a coronal oblique plane (indicated in b) was used to obtain another breath-hold turbo spin-echo image with the patient in the prone position (1,857/85, section thickness of 8 mm, field of view of 450 mm, and matrix of 276 x 512). Flow was measured in the pulmonary trunk just above the pulmonary valves (velocity mapping plane indicated).

View larger version (158K): [in a new window]   Figure 1c. MR images demonstrate the planes (lines) used to measure blood flow. (a) Coronal spin-echo image (942/30, section thickness of 6 mm, field of view of 380 mm, and matrix of 172 x 256) of the ascending aorta, with the plane used for velocity mapping indicated. (b) Sagittal breath-hold turbo spin-echo image (2,033/85, section thickness of 8 mm, field of view of 400 mm, and matrix of 230 x 512) obtained along the pulmonary trunk. (c) From b, a coronal oblique plane (indicated in b) was used to obtain another breath-hold turbo spin-echo image with the patient in the prone position (1,857/85, section thickness of 8 mm, field of view of 450 mm, and matrix of 276 x 512). Flow was measured in the pulmonary trunk just above the pulmonary valves (velocity mapping plane indicated).

View larger version (162K): [in a new window]   Figure 2. MR images show the modulus (upper panels) and corresponding phase (lower panels) used to outline the region of interest for flow measurements in the aorta (left panels: velocity encoding of 150 cm/sec, 40/5, a flip angle of 30°, a field of view of 380 mm, and a matrix of 192 x 256) and the pulmonary trunk just above the pulmonary valves (right panels: velocity encoding of 150 cm/sec, 40/5, a flip angle of 30°, a field of view of 380 mm, and a matrix of 256 x 256). a = aorta, p = pulmonary trunk.

View larger version (23K): [in a new window]   Figure 3a. Graphs show original data from one patient to demonstrate how (a) MR velocity mapping (volume in milliliters per second vs time in milliseconds) and (b) radionuclide angiography (counts per second vs time in seconds) were used to calculate QP/QS. In a, flow was measured in the pulmonary trunk (), the aorta (), and the pulmonary trunk again (•). QP/QS is calculated as the mean of the two measurements of pulmonary flow in liters per minute divided by the systemic flow in liters per minute to avoid physiologic drift in cardiac output. Note the repeatability of the two pulmonary flow measurements. In b, a gamma variate curve (dotted line a) is fitted to the original time activity data (thick solid line). Subtraction of curve a from the original data provides the recirculation data (thin solid line). A second gamma variate curve (dotted line b) is fitted to the recirculation data, and QP/QS is calculated from the areas under the curves as a/(a - b).

View larger version (24K): [in a new window]   Figure 3b. Graphs show original data from one patient to demonstrate how (a) MR velocity mapping (volume in milliliters per second vs time in milliseconds) and (b) radionuclide angiography (counts per second vs time in seconds) were used to calculate QP/QS. In a, flow was measured in the pulmonary trunk (), the aorta (), and the pulmonary trunk again (•). QP/QS is calculated as the mean of the two measurements of pulmonary flow in liters per minute divided by the systemic flow in liters per minute to avoid physiologic drift in cardiac output. Note the repeatability of the two pulmonary flow measurements. In b, a gamma variate curve (dotted line a) is fitted to the original time activity data (thick solid line). Subtraction of curve a from the original data provides the recirculation data (thin solid line). A second gamma variate curve (dotted line b) is fitted to the recirculation data, and QP/QS is calculated from the areas under the curves as a/(a - b).

View larger version (13K): [in a new window]   Figure 4. Graph shows findings at MR (MRI) velocity mapping versus findings at beaker and timer analysis to quantitate QP/QS in a phantom and line of equality. The mean error of the MR flow measurements is 1% ± 1.

View larger version (16K): [in a new window]   Figure 5a. Graphs show agreement between radionuclide angiography (RNA) and MR velocity mapping measurements of QP/QS in patients with left-to-right cardiac shunt. • = children and adolescents, = adults. (a) MR velocity mapping results are plotted against those of radionuclide angiography. Dashed line is line of equality. (b) Mean difference between findings at radionuclide angiography and findings at MR velocity mapping is 14% ± 13 (n = 24) and is essentially proportional to shunt size. From top to bottom, the lines represent mean + 2 SD, mean, and mean - 2 SD.

View larger version (21K): [in a new window]   Figure 5b. Graphs show agreement between radionuclide angiography (RNA) and MR velocity mapping measurements of QP/QS in patients with left-to-right cardiac shunt. • = children and adolescents, = adults. (a) MR velocity mapping results are plotted against those of radionuclide angiography. Dashed line is line of equality. (b) Mean difference between findings at radionuclide angiography and findings at MR velocity mapping is 14% ± 13 (n = 24) and is essentially proportional to shunt size. From top to bottom, the lines represent mean + 2 SD, mean, and mean - 2 SD.

View larger version (18K): [in a new window]   Figure 6. Graph shows that the mean difference between repeated MR flow measurements in liters per minute in the same vessel is -1% ± 5. Dashed line indicates line of equality.