Ultrasound Applied Physics University of Toronto Department of Medical Imaging Applied Physics Mini-Course #3 2016 Ultrasound Laboratory Manual and Examination Booklet 1/21/2016
Ultrasound Applied Physics Mini-Course #3 LABORATORY MANUAL January 21, 2016
MI Applied Physics 1 Winter 2015/2016 Ultrasound Imaging Lab Goal: Develop an understanding of how user settings of an ultrasound system can be manipulated to generate optimal images Part 1: Imaging Adjustments and System Characterization Total time allowed: 30 minutes In this section, you will learn the basics of adjusting imaging settings in order to produce the best images possible with the clinical scanner. These skills will then be applied to the task of characterizing the system performance in terms of resolution and penetration depth. The image below shows the transducer control board of the Philips iu22 ultrasound platform. This lab will primarily make use of the buttons boxed below:
MI Applied Physics 2 Winter 2015/2016 Above the control board is the touchscreen, which provides more advanced selection of options. This is used in tandem with the control board to change myriad features during run-time. The round knobs just below the touchscreen are used to control the values of the lowermost touchscreen items. For this portion of the lab, you will be using a CIRS tissue-mimicking characterization phantom. This is one of the industry standards in characterizing ultrasound systems and provides a number of lesions and wire point targets to determine system performance. The front of the phantom shows the layout of the targets through depth. Notice, in particular, the long axial line of targets, and the constellation targets on the right:
MI Applied Physics 3 Winter 2015/2016 The manufacturer provides relative distances of these wire targets on the datasheet:
MI Applied Physics 4 Winter 2015/2016 Section A: Resolution and Penetration Depth with Linear Arrays Step 1. Press the Transducer button, and then use the touch-screen to select the mid-frequency linear array probe, the L9-3. Use the touch-screen to select the Abd Bowel mode, which is optimized to provide maximum penetration depth on this probe. Once the settings have finalized, turn off the proprietary compounding and image enhancement by making sure XRES and SonoCT settings are disabled on the touch-screen. Next, make sure the transducer is optimized for these experiments by turning the res-speed knob just below the touch-screen as far as possible to the res side. Then adjust the 2D gain structure by pressing the 2D Opt button until it shows PEN. Step 2. Place a thin layer of ultrasound gel on the transducer surface and then couple the transducer to the surface of the characterization phantom LIGHTLY on the 0.7 db side. Pressing hard into the surface will only damage the phantom, and will not improve the images you acquire! Move the transducer around the phantom until you locate the axial line of wire targets. Step 3. Use the Depth knob to increase your maximum imaging depth to 14 cm, and use the Focus knob to place the focus at 10 cm in depth. Now adjust the Time-Gain Compensation (TGC) knobs and the 2D Gain settings until you have an image with good dynamic range and even image quality through depth. To freeze the image, press 'Freeze' on the console, and to capture the image, press 'Print'. Question 1: a) Based on the spacing of the wire targets, how deep is the most distal wire target you are able to resolve? b) At approximately what depth does the electronic noise overtake the tissue speckle signal? Step 4. Note the current MI in the upper right. Use the arrow on the touchscreen to move to the next page and find the Output Power parameter at the lower left. This is coupled to the knob below, which you can turn to change the imaging Mechanical Index. The MI is displayed at the upper right of the imaging screen. Question 2: How low can you bring the MI and still see tissue signal at a depth of 6 cm?
MI Applied Physics 5 Winter 2015/2016 Step 5. Return the MI to the original value. Move the transducer around the phantom top until you locate the resolution wire targets. These look like a constellation, with shortened spacing at each wire target pair toward the right and bottom of the phantom. Adjust the depth to 5 cm and bring the focus to 3 cm. Re-center the TGC knobs from your previous values and adjust the 2D gain and TGC until the image is even through depth with a wide dynamic range. Question 3: a) How close together are the closest axial targets you are still able to individually resolve? b) How close are the closest lateral targets you are still able to individually resolve? Step 6. Click the Transducer button and change the mode to SmPrtBrst, which is optimized to show superficial structures at higher resolution. Turn off any image enhancement features such as XRES, SonoCT, or Harmonic. On the touch-screen changing the Im Opt to RES. Now change the imaging Depth to 5 cm, and the Focus between 3 and 4 cm. Adjust the 2D Gain and TGC as needed to return the image to good quality. Now look at the constellation point targets again and determine the axial and lateral resolution limits. Question 4: a) Did changing the imaging mode on the same transducer produce a different result? b) How do you think changing the imaging mode adjusted the ultrasound parameters? Discuss three changes. Section B: Resolution and Penetration Depth with Curvilinear Arrays Step 7. Now you will look at how these penetration depth and resolution measurements are impacted by using a very different transducer the curvilinear C5-1 meant for imaging deep structures at lower frequencies. Because you can t couple the entire transducer to the phantom, there will be artifacts in the image from dead space on the sides. Don t try to press down harder to improve this. Use the Transducer button to switch to the C5-1 probe with Abd Bowel mode. Turn off the extra bells and whistles by touching the XRES, SonoCT, and Harmonic buttons. Set the imaging depth to 20 cm with the focus at 15 cm, and adjust the 2D gain and TGC to make an even image with maximal dynamic range. Make sure that the 'Im Opt' touch-screen button is set to 'PEN'. Adjust the Sector Width parameter on the touchscreen to minimize the coupling artifacts on the sides. Now find the axial depth wire targets as before.
MI Applied Physics 6 Winter 2015/2016 Question 5: a) Based on the spacing of the wire targets, how deep is the most distal wire target you are able to resolve? b) At approximately what depth does the electronic noise overtake the tissue speckle signal? Step 8. Note the current MI. Use the arrow on the touchscreen to move to the next page and find the Output Power parameter at the lower left. This is coupled to the knob below, which you can turn to change the imaging Mechanical Index. The MI is displayed at the upper right of the imaging screen. Question 6: How low can you bring the MI and still see tissue signal at a depth of 10 cm? Step 9. Return the MI to the original value. Move the transducer around the phantom top until you locate the resolution wire targets as before. Adjust the depth to 5 cm and bring the focus to 2-3 cm. Recenter the TGC knobs from your previous values and adjust the 2D gain and TGC until the image is even through depth with a wide dynamic range. Now find the axial and lateral resolution targets. Question 7: a) How close together are the closest axial targets you are still able to individually resolve? b) How close are the closest lateral targets you are still able to individually resolve? Step 10. Now explore the impact of the imaging mode presets on this answer by switching the 'Im Opt' touch-screen button to 'RES'. Question 8: a) Does this impact your lateral or axial resolution measurements?
MI Applied Physics 7 Winter 2015/2016 Section C: Lesions, Speckle, and Compounding Step 11. In the final step of this phantom characterization, you will qualitatively explore the impact of additional image processing features. Stay in the same imaging mode with the C5-1 transducer, but change the imaging depth to 10 cm with the focus at 5 cm. Find the 'big' anechoic lesion located approximately 7 cm in depth. Click the 'Zoom' button to bring up the region of interest prompt, and use the scroll ball and right click button to make the region as narrow as possible axially and laterally while keeping the entire lesion in view. When you're satisfied with the selection, click the 'Zoom' button again to enable the selection. Step 12. First explore switching between 'PEN' and 'RES' on the touch-screen as before and notice the impact this has on the speckle as well as your ability to discern lesion margins. Next, leave the 'RES' option on and switch on the 'XRES' feature. Notice any additional changes that this produced on lesion margins and speckle. Finally, enable the 'SonoCT' feature and notice any changes on lesion margins and speckle. Question 9: How much do these imaging features impact your ability to visualize the lesion? How much do they impact your ability to see the tissue 'texture' provided by the speckle? Question 10: How much deeper was the C5-1 probe able to image compared to the L9-3 in these characterizations? How much better was the L9-3 resolution than the C5-1 resolution in the best cases?
MI Applied Physics 8 Winter 2015/2016 [OPTIONAL - 2 Marks] Section D: When Things Go Wrong... If you have time remaining, completion of this section and a correct answer to the question will count as an extra 2 marks toward the timed competition in the next station. Step D. Using what you've learned about the Philips iu22 ultrasound platform, switch to the L17-5 imaging probe and select an imaging mode appropriate to provide optimal resolution at superficial depths. Adjust any imaging parameters you wish to obtain the best possible image of the most superficial 'constellation' resolution targets. Present this view to the station supervisor when you're satisfied with it. They will judge the choice of settings and award 1 mark if they are satisfactory. Question D: Do you notice any artifacts in the image? What might the source of these artifacts be? [OPTIONAL - 4 Marks] Section E: Imaging Blood Flow If you have time remaining, completion of this section and a correct answer to the question will count as an extra 4 marks toward the timed competition in the next station. Step E1. Using what you've learned about the Philips iu22 ultrasound platform, switch to a linear array imaging probe and select an imaging mode appropriate to provide optimal resolution at superficial depths. Adjust any imaging parameters you wish to obtain the best possible image of the most superficial targets. Your task is to image the brachial artery of a volunteer from your group. Choose a place along the arm to get a good acoustic window and align the artery to be along the axis of the transducer face. To anticipate using Doppler, which is sensitive to axial flow, it's best to have an angle relative to the transducer face. Step E2. When you are satisfied with the B-mode image, enable Pulse-Wave (PW) Doppler by pressing the 'PW' button on the console. Use the trackball and cursors to move the PW window to the middle of the artery, and adjust the correction angle using the touch-screen to be aligned parallel to the artery. To interleave the PW Doppler and B-mode (which provides better guidance), enable the 'Simult' touchscreen option. Step E3. Capture your team member's PW Doppler spectrum by pressing the 'update' button on the console. Adjust the transducer, PW window location (using the trackball), and the touchscreen options to get the best spectrum possible showing pulsatile flow with little spectral broadening. Adjust the baseline and scale as needed to eliminate aliasing and other artifacts. Record the PW spectrum for at least 3 heartbeats by pressing the 'Capture' button once to start, and once to stop. Present the images and Doppler spectrum you acquired to the station supervisor. Points will be awarded based on image quality
MI Applied Physics 9 Winter 2015/2016 Part 2: Anatomical Imaging: The Abominable Abdominal Challenge Total time allowed: 30 minutes In this section, you will image an abdominal phantom to practice locating anatomical sites. For most of this section, it will be advantageous to use the C5-1 transducer, although you may switch to the linear array for more superficial targets. Instructions Use the system interface to select the C5-1 transducer and adjust settings to produce an even image Capture your team's 'best' image of the following structures using appropriate imaging settings. You will likely need to adjust settings as you change targets. Annotate the image in the bottom right of the screen with the corresponding number by using the 'Annotate' button on the console and the keyboard underneath the console. Change the location of the annotation using the trackball. Place a cursor marker on the structure/feature under question. To capture an image, use the 'Print' button the on the console. The images can be stored in any order. 2 marks awarded per question. Note: There are 2 stand-alone questions that do not require the ultrasound system. Please identify the following (1.5 minutes per target): 1. Evidence of peri-hepatic bleeding 2. Posterior wall of the urinary bladder 3. Abdominal aortic aneurysm 4. Major calyx of the left kidney 5. Cardiac tamponade 6. Evidence of pelvic bleeding 7. Evidence of cholecystitis 8. Spleen 9. Evidence of pleural hemorrhage 10. Pancreas 11. Vena cava 12. Transverse colon 13. Tumour of the descending colon
MI Applied Physics 10 Winter 2015/2016 Stand-Alone Questions 1. Draw the beam pattern from the following transducers: linear, curvilinear, phased array. Indicate and explain, if possible, where the resolution would be the poorest in each case. Picture of linear array Picture of phased array Picture of curvilinear array 2. Define (and draw) a speckle pattern. What system settings can be used to influence the appearance of speckle? Describe at least two contributors.