Clinical feasibility of noninvasive visualization of lymphatic flow with principles of spin labeling MR imaging: implications for lymphedema assessment

Abstract

Purpose: To extend a commonly used noninvasive arterial spin labeling magnetic resonance (MR) imaging method for measuring blood flow to evaluate lymphatic flow.

Materials and methods: All volunteers (n = 12) provided informed consent in accordance with institutional review board and HIPAA regulations. Quantitative relaxation time (T1 and T2) measurements were made in extracted human lymphatic fluid at 3.0 T. Guided by these parameters, an arterial spin labeling MR imaging approach was adapted to measure lymphatic flow (flow-alternating inversion-recovery lymphatic water labeling, 3 × 3 × 5 mm) in healthy subjects (n = 6; mean age, 30 years ± 1 [standard deviation]; recruitment duration, 2 months). Lymphatic flow velocity was quantified by performing spin labeling measurements as a function of postlabeling delay time and by measuring time to peak signal intensity in axillary lymph nodes. Clinical feasibility was evaluated in patients with stage II lymphedema (three women; age range, 43-64 years) and in control subjects with unilateral cuff-induced lymphatic stenosis (one woman, two men; age range, 31-35 years).

Results: Mean T1 and T2 relaxation times of lymphatic fluid at 3.0 T were 3100 msec ± 160 (range, 2930-3210 msec; median, 3200 msec) and 610 msec ± 12 (range, 598-618 msec; median, 610 msec), respectively. Healthy lymphatic flow (afferent vessel to axillary node) velocity was 0.61 cm/min ± 0.13 (n = 6). A reduction (P < .005) in lymphatic flow velocity in the affected arms of patients and the affected arms of healthy subjects with manipulated cuff-induced flow reduction was observed. The ratio of unaffected to affected axilla lymphatic velocity (1.24 ± 0.18) was significantly (P < .005) higher than the left-to-right ratio in healthy subjects (0.91 ± 0.18).

Conclusion: This work provides a foundation for clinical investigations whereby lymphedema etiogenesis and therapies may be interrogated without exogenous agents and with clinically available imaging equipment. Online supplemental material is available for this article.

Figure 1a:

Relaxation time measurements. Graphs of (a) inversion recovery and (b) exponential spin-echo decay of a representative lymphatic fluid sample at 38°C. Experimental data (●) and fit (solid line) are shown (Equations 1 and 2, respectively). (c, d) In vivo MR images of lymph nodes (arrows) acquired with (c) DWIBS and (d) without (left) and with (right) inversion prepulse with echo-planar imaging. Inversion prepulse was placed at the expected null point (inversion time, 1.4 sec; repetition time, 4 sec) of lymphatic water, calculated with T1 of 3100 msec measured from the ex vivo lymphatic sample. (e) Quantitative analysis of signal in the nodes shows that signal intensity after longitudinal nulling is not significantly different from noise signal. This provides support for the ex vivo T1 measurements reflecting in vivo lymphatic water T1. Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the most extreme values in the data. * * * = P < .001.

Figure 1b:

Relaxation time measurements. Graphs of (a) inversion recovery and (b) exponential spin-echo decay of a representative lymphatic fluid sample at 38°C. Experimental data (●) and fit (solid line) are shown (Equations 1 and 2, respectively). (c, d) In vivo MR images of lymph nodes (arrows) acquired with (c) DWIBS and (d) without (left) and with (right) inversion prepulse with echo-planar imaging. Inversion prepulse was placed at the expected null point (inversion time, 1.4 sec; repetition time, 4 sec) of lymphatic water, calculated with T1 of 3100 msec measured from the ex vivo lymphatic sample. (e) Quantitative analysis of signal in the nodes shows that signal intensity after longitudinal nulling is not significantly different from noise signal. This provides support for the ex vivo T1 measurements reflecting in vivo lymphatic water T1. Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the most extreme values in the data. * * * = P < .001.

Figure 1c:

Relaxation time measurements. Graphs of (a) inversion recovery and (b) exponential spin-echo decay of a representative lymphatic fluid sample at 38°C. Experimental data (●) and fit (solid line) are shown (Equations 1 and 2, respectively). (c, d) In vivo MR images of lymph nodes (arrows) acquired with (c) DWIBS and (d) without (left) and with (right) inversion prepulse with echo-planar imaging. Inversion prepulse was placed at the expected null point (inversion time, 1.4 sec; repetition time, 4 sec) of lymphatic water, calculated with T1 of 3100 msec measured from the ex vivo lymphatic sample. (e) Quantitative analysis of signal in the nodes shows that signal intensity after longitudinal nulling is not significantly different from noise signal. This provides support for the ex vivo T1 measurements reflecting in vivo lymphatic water T1. Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the most extreme values in the data. * * * = P < .001.

Figure 1d:

Relaxation time measurements. Graphs of (a) inversion recovery and (b) exponential spin-echo decay of a representative lymphatic fluid sample at 38°C. Experimental data (●) and fit (solid line) are shown (Equations 1 and 2, respectively). (c, d) In vivo MR images of lymph nodes (arrows) acquired with (c) DWIBS and (d) without (left) and with (right) inversion prepulse with echo-planar imaging. Inversion prepulse was placed at the expected null point (inversion time, 1.4 sec; repetition time, 4 sec) of lymphatic water, calculated with T1 of 3100 msec measured from the ex vivo lymphatic sample. (e) Quantitative analysis of signal in the nodes shows that signal intensity after longitudinal nulling is not significantly different from noise signal. This provides support for the ex vivo T1 measurements reflecting in vivo lymphatic water T1. Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the most extreme values in the data. * * * = P < .001.

Figure 1e:

Relaxation time measurements. Graphs of (a) inversion recovery and (b) exponential spin-echo decay of a representative lymphatic fluid sample at 38°C. Experimental data (●) and fit (solid line) are shown (Equations 1 and 2, respectively). (c, d) In vivo MR images of lymph nodes (arrows) acquired with (c) DWIBS and (d) without (left) and with (right) inversion prepulse with echo-planar imaging. Inversion prepulse was placed at the expected null point (inversion time, 1.4 sec; repetition time, 4 sec) of lymphatic water, calculated with T1 of 3100 msec measured from the ex vivo lymphatic sample. (e) Quantitative analysis of signal in the nodes shows that signal intensity after longitudinal nulling is not significantly different from noise signal. This provides support for the ex vivo T1 measurements reflecting in vivo lymphatic water T1. Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the most extreme values in the data. * * * = P < .001.

Figure 2a:

Lymph node identification. (a-c) Representative DWIBS MR images in a 30-year-old male patient clearly show the lymph nodes across orthogonal axes within the white rectangles. A typical axial section (c) along the white line in a is used to guide the section location for spin labeling. (d) Corresponding spin labeling MR image in a control subject. Location and planning were guided by DWIBS contrast. (e) DWIBS MR image overlaid on d and thresholded to identify different structures (green = cerebrospinal fluid, yellow = lymph, red = outline of cardiac tissue and major blood vessels) and to draw the regions of interest (two to four voxels) to evaluate lymph kinetic curves.

Figure 2b:

Lymph node identification. (a-c) Representative DWIBS MR images in a 30-year-old male patient clearly show the lymph nodes across orthogonal axes within the white rectangles. A typical axial section (c) along the white line in a is used to guide the section location for spin labeling. (d) Corresponding spin labeling MR image in a control subject. Location and planning were guided by DWIBS contrast. (e) DWIBS MR image overlaid on d and thresholded to identify different structures (green = cerebrospinal fluid, yellow = lymph, red = outline of cardiac tissue and major blood vessels) and to draw the regions of interest (two to four voxels) to evaluate lymph kinetic curves.

Figure 2c:

Lymph node identification. (a-c) Representative DWIBS MR images in a 30-year-old male patient clearly show the lymph nodes across orthogonal axes within the white rectangles. A typical axial section (c) along the white line in a is used to guide the section location for spin labeling. (d) Corresponding spin labeling MR image in a control subject. Location and planning were guided by DWIBS contrast. (e) DWIBS MR image overlaid on d and thresholded to identify different structures (green = cerebrospinal fluid, yellow = lymph, red = outline of cardiac tissue and major blood vessels) and to draw the regions of interest (two to four voxels) to evaluate lymph kinetic curves.

Figure 2d:

Lymph node identification. (a-c) Representative DWIBS MR images in a 30-year-old male patient clearly show the lymph nodes across orthogonal axes within the white rectangles. A typical axial section (c) along the white line in a is used to guide the section location for spin labeling. (d) Corresponding spin labeling MR image in a control subject. Location and planning were guided by DWIBS contrast. (e) DWIBS MR image overlaid on d and thresholded to identify different structures (green = cerebrospinal fluid, yellow = lymph, red = outline of cardiac tissue and major blood vessels) and to draw the regions of interest (two to four voxels) to evaluate lymph kinetic curves.

Figure 2e:

Lymph node identification. (a-c) Representative DWIBS MR images in a 30-year-old male patient clearly show the lymph nodes across orthogonal axes within the white rectangles. A typical axial section (c) along the white line in a is used to guide the section location for spin labeling. (d) Corresponding spin labeling MR image in a control subject. Location and planning were guided by DWIBS contrast. (e) DWIBS MR image overlaid on d and thresholded to identify different structures (green = cerebrospinal fluid, yellow = lymph, red = outline of cardiac tissue and major blood vessels) and to draw the regions of interest (two to four voxels) to evaluate lymph kinetic curves.

Figure 3:

Unobstructed lymphatic flow results. Lymphatic and blood water magnetization as a function of postlabeling delay times in six separate healthy subjects. In-plane dimensions of lymph nodes evaluated for each subject are also reported. Note that blood signal increases quickly owing to the short T1 of blood water and fast blood water velocity. Alternatively, signal in the axillary lymph node increases much later, because of the much slower velocity of lymph fluid. The relatively rapid rise and fall of the lymphatic curve is consistent with mixing of lymphatic water in the node and finite node dwell times, similar to the macrovascular blood compartment in arterial spin labeling experiments (Appendix E3 [online]). F = female, M = male, ROI = region of interest.

Figure 4a:

Obstructed lymphatic flow results. (a) Lymphatic flow curves for a representative healthy 31-year-old male volunteer with unilateral cuff steno-occlusion of lymphatic fluid (pressure, 60 mmHg) (top) and for a 60-year-old female patient with stage II lymphedema secondary to unilateral breast cancer mastectomy (bottom). In healthy subjects and patients, a delay in lymphatic arrival times on the affected side relative to the unaffected side is observed. Additionally, multiple arrival times are found, consistent with multiple afferent vessels delivering lymphatic water to the node. (b) Ratio of lymphatic flow velocity in the unaffected arm to that in the affected arm was significantly higher (1.24 ± 0.18, P < .005) in the six impaired subjects when compared with lymphatic velocity ratio in the left arm to that in the right arm in healthy subjects shown in Figure 3 (0.9124 ± 0.08). Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the extreme values measured in this data. Dashed line represents the line of unity indicating identical lymph velocity in both arms. * * =P < .005.

Figure 4b:

Obstructed lymphatic flow results. (a) Lymphatic flow curves for a representative healthy 31-year-old male volunteer with unilateral cuff steno-occlusion of lymphatic fluid (pressure, 60 mmHg) (top) and for a 60-year-old female patient with stage II lymphedema secondary to unilateral breast cancer mastectomy (bottom). In healthy subjects and patients, a delay in lymphatic arrival times on the affected side relative to the unaffected side is observed. Additionally, multiple arrival times are found, consistent with multiple afferent vessels delivering lymphatic water to the node. (b) Ratio of lymphatic flow velocity in the unaffected arm to that in the affected arm was significantly higher (1.24 ± 0.18, P < .005) in the six impaired subjects when compared with lymphatic velocity ratio in the left arm to that in the right arm in healthy subjects shown in Figure 3 (0.9124 ± 0.08). Red line represents the median, while the box represents the 25th and 75th percentiles. Error bars indicate the extreme values measured in this data. Dashed line represents the line of unity indicating identical lymph velocity in both arms. * * =P < .005.