Guide to Small Animal Vascular Imaging using the Vevo 770 Micro-Ultrasound System

Transcription

1 Guide to Small Animal Vascular Imaging using the Vevo 770 Micro-Ultrasound System January 2007 Objectives: After completion of this module, the participant will be able to accomplish the following: Understand basic doppler principles Make adjustments on the Vevo micro-ultrasound system to obtain and optimize the required images Position the micro-ultrasound RMV scanhead to acquire the necessary imaging views, and Review estimated values for main calculations A Note on RMV Scanhead Selection for Vascular Imaging: Appropriate selection of RMV scanheads for vascular imaging is critical to the resolution and definition obtained. For the Vevo 770, recommended RMV scanheads are the 704 and the 707B. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

2 Basic Doppler Principles Ultrasound images of flow are essentially obtained from measurements of movement. In ultrasound scanners, a series of pulses are transmitted to detect movement of blood. Echoes from stationary tissue are the same from pulse to pulse. Echoes from moving scatterers exhibit slight differences in the time for the signal to be returned to the receiver (Figure 1). These differences can be measured as a direct time difference or, more usually, in terms of a phase shift from which the Doppler frequency is obtained (Figure 2). They are then processed to produce either a Doppler sonogram. Figure 1 Ultrasound velocity measurement. The diagram shows a scatterer S moving at velocity V with a beam/flow angle q.the velocity can be calculated by the difference in transmit-to-receive time from the first pulse to the second (t2), as the scatterer moves through the beam. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

3 Figure 2: Doppler ultrasound. Doppler ultrasound measures the movement of the scatterers through the beam as a phase change in the received signal. The resulting Doppler frequency can be used to measure velocity if the beam/flow angle is known. As seen from Figures 1 and 2, there has to be motion in the direction of the beam; if the flow is perpendicular to the beam, there is no relative motion from pulse to pulse. The size of the Doppler signal is dependent on: 1. Blood velocity: as velocity increases, so does the Doppler frequency. 2. Ultrasound frequency: higher ultrasound frequencies allow increased Doppler frequencies. As in B-mode, lower ultrasound frequencies have better penetration. 3. The choice of frequency is a compromise between better sensitivity to flow or better penetration. 4. The angle of insonation: the Doppler frequency increases as the Doppler ultrasound beam becomes more aligned to the flow direction (the angle q between the beam and the direction of flow becomes smaller). This is of the utmost importance in the use of Doppler ultrasound. The implications are illustrated schematically in Figure 3. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

4 Figure 3 - Effect of the Doppler angle in the sonogram. (A) higher-frequency Doppler signal is obtained if the beam is aligned more to the direction of flow. In the diagram, beam (A) is more aligned than (B) and produces higher-frequency Doppler signals. The beam/flow angle at (C) is almost 90 and there is a very poor Doppler signal. The flow at (D) is away from the beam and there is a negative signal. All types of Doppler ultrasound equipment employ filters to cut out the high amplitude, low-frequency Doppler signals resulting from tissue movement, for instance due to vessel wall motion. Filter frequency can usually be altered by the user, for example, to exclude frequencies below 50, 100 or 200 Hz. This filter frequency limits the minimum flow velocities that can be measured. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

5 I. COMMON CAROTID ARTERY Location: The common carotid artery lies on either side of the trachea in the animal s neck. Scanhead Position: The scanhead is positioned with the notch pointing toward the chin of the animal. A slight cranial angle may be required in order to obtain the correct angle for the Doppler waveform. Figure 1: The carotid artery at the bifurcation. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

6 Figure 2: The common carotid artery. Figure 3: Pulsed wave Doppler of the common carotid artery. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

7 II. INTERNAL CAROTID ARTERY Location: Internal carotid artery is visualized at the bifurcation of the common carotid artery as the more posterior branch. Scanhead Position: The scanhead is positioned with the notch pointing toward the chin of the animal. The scanhead should be angled cranially to achieve an angle of 60 degrees or less for the Doppler waveform. **The flow in the internal carotid artery is typically with a higher diastolic component than in the external carotid artery. Figure 4: The bifurcation of the carotid artery showing the internal and external carotid artery branches. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

8 Figure 5: The internal carotid artery with the pulsed Doppler wire overlay. Figure 6: The internal carotid artery pulsed Doppler waveform. There is typically a higher diastolic component with the internal carotid artery as it leads to a low resistance vascular bed VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

9 III. EXTERNAL CAROTID ARTERY Location: The external carotid artery is visualized at the carotid bifurcation as the more anterior branch. Scanhead Position: The scanhead is positioned with the notch pointing toward the chin of the animal. The scanhead should be angled cranially or caudally depending on the angle of the vessel to best achieve an angle of 60 degree or less for optimum Doppler waveform. **The flow in the external carotid artery, as it is going to a higher resistance vascular bed, has a higher systolic velocity and lower diastolic velocity than is seen in the internal carotid artery. Figure 7: Image of the carotid artery bifurcation. The external carotid can be seen more anterior than the internal carotid artery. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

10 Figure 8: The external carotid artery with the pulsed Doppler wire overlay. Figure 9: The external carotid artery pulsed Doppler waveform. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

11 IV. AORTA Location: The abdominal aorta can be visualized in the mid abdomen below the diaphragm and just to the left of the animal s midline. Scanhead position: The orientation that is easiest to find the aorta with is the transverse position with the notch of the transducer to the left side of the animal. The aorta can be seen as a round throbbing object anterior to the spine with the Inferior Vena Cava as a more oval-shaped object to the left of the aorta on the image (on the animal s right side). Figure 10: Transverse image of the Inferior Vena Cava and the Abdominal Aorta. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

12 Figure 11: Sagittal view of the abdominal aorta with the cranial artery branch leading off the anterior aspect of the aorta. Figure 12: Sagittal view of the abdominal aorta with a 60 degree angle of the pulsed Doppler overlay to obtain the Doppler waveform. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

13 Figure 13: Sagittal view of the abdominal aorta with the pulsed Doppler waveform. V. INFERIOR VENA CAVA (IVC) Location: The inferior vena cava is located along the midline of the abdomen. Scanhead Position: The inferior vena cava can be seen in transverse view with the notch of the transducer located to the left side of the animal. The abdominal aorta can be seen to the right of the IVC (on the animal s left side) in this view. For the sagittal view, orientate the scanhead with the notch towards the head of the mouse. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

14 Figure 14: The Inferior Vena Cava can be visualized in sagittal view. Figure 15: Pulsed Doppler waveform of the Inferior Vena Cava. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

15 VI. ILIAC ARTERIES Location: The iliac arteries are visualized in the pelvic region of the animal and can be seen from the bifurcation of the aorta into the right and left iliac arteries just below midline of the animal. Scanhead Position: The scanhead can be placed first in the transverse plane with the scanhead notch pointing towards the animal s left side (make sure the orientation of the notch coincides with the orientation of the image on the screen). The iliac arteries can be seen as the scanhead is moved in transverse plane in a caudal direction. For the sagittal view of the iliac arteries turn the scanhead clockwise from a sagittal plane to achieve the long axis of the right iliac artery. For the left iliac artery, turn the scanhead counterclockwise from the sagittal plane to obtain the long axis. Slight cranial or caudal angulation of the scanhead will be required to obtain the correct angle for the Doppler waveform. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

16 Figure 16: 2D image with a long axis image of an iliac artery showing the Doppler. VII. FEMORAL ARTERIES Location: The femoral arteries arise from the iliac arteries as the artery passes through the inguinal canal. The femoral arteries can be visualized midline of the proximal leg. Scanhead Position: The notch of the scanhead is kept in the same plane for the femoral arteries as the iliac arteries. The scanhead should be moved along the long axis of the leg to follow the artery. Slight clockwise/counterclockwise rotation of the scanhead may be required to maintain the artery in the long axis, as well as cranial or caudal angulation to achieve the proper 60 degree angle for the Doppler waveform. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

17 Figure 17: Image of the femoral artery in the upper thigh of the animal. Figure 18: 2D image of the femoral artery in the long axis with the Doppler overlay demonstrating an angle of 60 degrees. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

18 Figure 19: Pulsed wave Doppler waveform of the femoral artery. VIII. ILIAC ARTERIES Location: The iliac arteries are visualized in the pelvic region of the animal and can be seen from the bifurcation of the aorta into the right and left iliac arteries just below midline of the animal. Scanhead Position: The scanhead can be placed first in the transverse plane with the scanhead notch pointing towards the animal s left side (make sure the orientation of the notch coincides with the orientation of the image on the screen). The iliac arteries can be seen as the scanhead is moved in transverse plane in a caudal direction. For the sagittal view of the iliac arteries turn the scanhead clockwise from a sagittal plane to achieve the long axis of the right iliac artery. For the left iliac artery, turn the scanhead counter-clockwise from the sagittal plane to obtain the long axis. Slight cranial or caudal angulation of the scanhead will be required to obtain the correct angle for the Doppler waveform. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

19 Figure 20: Image of the iliac artery in the lower pelvis of a mouse. Figure 21: Pulsed Doppler waveform of the iliac artery. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

20 IX. FEMORAL ARTERIES Location: The femoral arteries arise from the iliac arteries as the artery passes through the inguinal canal. The femoral arteries can be visualized midline of the proximal leg. Scanhead Position: The notch of the scanhead is kept in the same plane for the femoral arteries as the iliac arteries. The scanhead should be moved along the long axis of the leg to follow the artery. Slight clockwise/counterclockwise rotation of the scanhead may be required to maintain the artery in the long axis, as well as cranial or caudal angulation to achieve the proper 60 degree angle for the Doppler waveform. Figure 22: Image shows the femoral artery in the upper leg of a mouse. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

21 Figure 23: Pulsed Doppler overlay in femoral artery. Figure 24: Pulsed Doppler waveform of the femoral artery. The flow is seen below the baseline as the arterial flow is going away from the transducer. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

22 X. RENAL ARTERIES Location: The renal arteries can be seen in transverse view arising from the abdominal aorta and then leading into the renal hilum. Scanhead Position: The transducer should be placed in a transverse plane so that the notch of the scanhead is pointing to the left side of the animal. Obtain a transverse view of the aorta and then with lateral movements move to the right or left of midline to visualize the renal arteries leading into the renal hilum of the kidney. Figure 25: Transverse view of the left Main Renal Artery arising from the aorta. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

23 Figure 26: Lt Renal Artery pulsed Doppler waveform. The flow is below the Doppler baseline as the arterial flow is going away from the transducer towards the kidney which is slightly posterior to the abdominal aorta. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

24 Figure 27: The left renal vein is visualized with the pulsed Doppler flow above the baseline as the venous flow is returning to the IVC and therefore the flow is going towards the transducer. Figure 28: Transverse view of the left Renal vessels. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

25 XI. HEPATIC VASCULATURE Location: There are two venous systems within the liver. The portal venous system takes blood to the liver via the main portal vein that then branches into the right and left branches. These are best demonstrated in the transverse view. The hepatic veins drain the blood from the liver into the IVC. These veins are also best visualized in the transverse view. There are three main hepatic veins that drain posteriorly and can be seen draining into the IVC. Scanhead position: The liver parenchyma as well as both venous systems are best seen in the transverse position with the notch of the scanhead pointing to the left side of the animal. The image will have to be inverted so that the orientation is such that the animal s left side is on the right side of the screen. A slight cephalad angle to the probe may be necessary in some animals to better visualize the hepatic veins as they drain into the IVC. Figure 29: Hepatic veins are visualized with the scanhead in a transverse orientation. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

26 Figure 30: PW Doppler overlay within the hepatic vein. Figure 31: Hepatic venous Doppler waveform. The direction of the flow is away from the scanhead towards the posterior aspect of the animal. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

27 Figure 32: Transverse view of the liver showing another hepatic vein. Figure 33: Middle hepatic vein in transverse view of the liver. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

28 Figure 34: Transverse view of the left lobe of the liver demonstrating the left branch of the portal vein. Figure 35: Image demonstrating PW Doppler overlay within left portal vein. VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v

29 Figure 36: Hepatic portal vein flow with the waveform above the baseline as the flow in this venous system is leading into the liver and therefore towards the scanhead. For more information or assistance with any imaging procedures, please contact VisualSonics at or T VisualSonics Workbook: Guide to Vascular Imaging Using the Vevo 770 v