Cleveland Family Study

10.10 Scan Technique

10.10.1 2-D Image Acquisition

1. Prior to the scanning procedure, the patient will rest for 15 minutes. The start of the rest period will be recorded on the data sheet.
2. At the end of the 15-minute rest period, the S-VHS VCR will be set to the “record” position.
3. Gel will be applied to the scanhead and the cable will be draped over the ultrasonographer’s shoulder to minimize cable tension.
   • The linear array will be held as one would hold a pencil to have maximum control of the ultrasound beam.
   • The ultrasonographer’s forearm, wrist, and hand will rest on the patient’s forearm. This reduces fatigue and encourages the patient not to move his/her arm during the exam. Additionally, this allows the ultrasonographer to maintain the same position so that the pre- and post-stimulus measurements will be obtained from the identical segment of the artery. 4.The scanhead will be oriented sagittally with the index positioned superiorly. This results in the proximal portion of the artery being displayed on the left side of the video monitor and the distal end on the right. At this point the S-VHS VCR record function will be activated. 5.The color flow will be activated to rapidly identify the brachial artery.
   • Since a 90º angle of incidence will be maintained throughout the procedure to maximize 2-D image quality, it will be necessary to steer the color box –20º to acquire a sufficient color Doppler signal.
4. The scanhead will be placed on the lateral surface of the patient’s procedure arm, immediately distal to the BP cuff, and the beam will be angled posterio-medially. The beam will be directed through the arm above the level of the humerus through the biceps brachii toward the brasilic vein and brachial artery.
5. The face of the scanhead will then be moved medially with a sweeping, not a sliding, motion until the artery is located. Depending on the patient’s arm the starting point of the sweeping motion may need to be more anterior or antero-medial. The reason for this approach will be so that a standoff with its complications (i.e., the probe can slip on the standoff and the standoff can slip on the arm) will be prevented.
   • When the artery is initially visualized, it typically will be displayed diagonally on the screen. This means that the beam will not be tangent to the artery. As a result, the vessel walls will be indistinct, making precise measurement of the internal diameter and less accurate. The remedy for this will be to think of the scanhead face as the plantar surface of a foot. More downward pressure will be applied on the proximal end (toe) of the linear array.
   • When the beam is tangent to the artery it will appear horizontally on the screen and there will be a significant improvement in the definition of the borders. 2-D beam steering should not be used to improve the intimal definition of a diagonally displayed artery. Such images are more difficult to measure.
6. Once the artery is horizontally displayed, the color flow will be switched off. The focal zones will then be positioned at both the anterior and posterior walls of the artery.
   • If the ultrasound machine only has one focal zone it will be positioned at the intimal border that is least well visualized. Typically, the anterior intimal border will be less well visualized, since the blood-filled lumen provides enhancement of the posterior wall.
7. The time gain compensation (TGC) and receive gain settings will be adjusted so that the tissue will be optimally displayed, and the lumen will be relatively sonolucent.
   • The diameter of the artery will be evaluated to make certain the proximal and distal ends are equal in diameter.
   • If not, the sagittal plane of the beam will not be parallel to the artery. To remedy this, the scanhead will be rotated (like a screwdriver) slightly clockwise or counter-clockwise until the artery is the same diameter over its entire length. It will take perseverance and patience to maintain the “toe” pressure/angle as the “screwdriver” angle of the scanhead is rotated.
8. The lumen will then be evaluated.
   • If there is an organized collection of echos centered in the lumen over the full length of the artery, the beam will be too close to either the medial or lateral wall of the artery. The solution will be to slide the scanhead either laterally or medially until the lumen is relatively echo-free. The beam will now be centered in the lumen.
9. The patient’s procedure arm will be surveyed from three approaches (lateral, anterior, and anterio-medial) to determine which approach will yield the best acoustic window for visualizing the brachial artery. As the scanhead is moved more medially, the artery will be displayed closer to the surface of the arm. Consequently, the TGC, transmit and receive gain controls will need to be adjusted.
10. The procedure will not be continued until the best acoustic window has been found for visualizing the brachial artery.
    • The anterior and posterior borders of the displayed image will be critically evaluated. A 1.5 cm wide x 1 cm deep zoom box will be positioned over the most well defined portion of the image and the high definition zoom function will be activated. The anterior and posterior intima will now be readily obvious.
    • When first learning this technique it may be a challenge to display both the anterior and the posterior intima simultaneously. It may be necessary to adjust the persistence to facilitate the simultaneous display of the anterior and posterior intima.
    • Once the optimum acoustic window has been found, which yields a highly detailed image, neither the scanhead nor the zoom box’s horizontal position will be moved for the duration of the procedure. Also, the patient’s procedure hand and arm should remain in the same position until the procedure is completed.
11. The high quality end-diastolic frames will be printed. This image will be placed top of the keyboard directly under the video monitor for comparison to all subsequent images. This will ensure that the same segment of the artery is consistently imaged. One copy of the image will be retained and put in the patient file.

The highly detailed zoomed image will be held as steady as possible for one minute. The image will be evaluated using the following criteria:

• Vertically centered
• Horizontally displayed (90º angle of insonation)
• Anterior and posterior intima parallel to each other over the full width of the image (the proximal diameter must be equal to the distal diameter)
• Sonolucent lumen (especially without organized echos in the center of the lumen)
• Optimal dynamic range/compression and persistence to differentiate the intima and medial layers
• Proper adjustment of transmit power, receive gain, and TGC
• Correct annotation