Abstract
The aim of this chapter is to explain the basic principles of gynaecology ultrasound for all those who are beginning to learn to perform scans, especially transvaginal ultrasound. These same principles will also benefit those who are keen to improve their scanning skills. In this chapter, we shall focus initially on the ultrasound machine itself and then on the scanning techniques, which will help you either as a beginner or to improve your scanning capability. Chapter 3 will focus on awkward or difficult clinical scenarios.
The aim of this chapter is to explain the basic principles of gynaecology ultrasound for all those who are beginning to learn to perform scans, especially transvaginal ultrasound. These same principles will also benefit those who are keen to improve their scanning skills. In this chapter, we shall focus initially on the ultrasound machine itself and then on the scanning techniques, which will help you either as a beginner or to improve your scanning capability. Chapter 3 will focus on awkward or difficult clinical scenarios.
Adopting a systematic approach to gynaecology scanning (pelvic scan) is essential. One could start scanning in the longitudinal view and then move to a transverse view. Anatomically, scanning the uterus first makes most sense, followed by the right and then the left ovary and adnexa. It is not uncommon that one, especially in the initial stages of training, may focus on an obvious pathology, e.g. a large ovarian cyst that is evident at the start of examination, and subsequently may become distracted and forget to scan other pelvic structures. A systematic approach to scanning will avoid such unnecessary omissions in scanning structures that form part of routine examination.
Ultrasound Equipment Used in Gynaecological Scanning
Machine and Keyboard
Knowledge of your machine, both for a beginner and an experienced scanner using a new machine before starting to scan, is an essential step in getting the best out of your equipment. Switching on modern machines is a bit like switching on a laptop or a computer, whereas if you have an older machine you will see an on/off switch on the side of the machine. Once the machine has been switched on, it may take one or two minutes to boot-up, as it is generally based on a Windows® environment. This gives you a good opportunity to have a look at the machine’s keyboard and screen. The keyboard can be daunting for beginners; it is advisable to initially identify a few important buttons (Figure 1.1a) before one starts scanning, such as:
1. freeze, to capture an image once obtained;
2. frequency;
3. measurement and set button (allowing one to obtain additional measurements);
4. greyscale/gain;
5. depth;
6. focus;
7. left/right and up/down screen display buttons;
8. save and print options; and
9. Doppler and 3D scanning functions.
(b) A touch screen giving options to select ultrasound settings for different organs. Frequency, angle, focal zone, up/down and right/left modes of scanning are among the basic functions which will be useful for a beginner. The touch screen is dynamic and hence selection of the options allows one to choose appropriate settings while scanning.
Some ultrasound machines, in addition to having a keyboard, may have an interactive touch screen (see Figures 1.1b and 1.2). It is important to understand that these touch screens are dynamic, so the display will show options for each function. For example, frequency display, on tapping the screen, will show three options: normal, resolution and penetrative mode. The penetrative mode is a lower-frequency setting and hence allows us to see deeper structures such as large fibroids. Higher frequency is generally good for smaller structures but specifically designed probes have made it easier to select the correct frequency. Hence, knowledge of potential options for each function is useful to ensure best use of the equipment. Those who have already achieved basic scanning skills may wish, in addition, to familiarize themselves with the Doppler and 3D scanning functions on the keyboard. It may be helpful to have a skilled scanner or systems specialist to demonstrate these functions. Some machines allow you to save individual frequently used settings, displayed as a personalized option to select before one starts scanning, especially where there are multiple users of the same machine. Machines may also have organ-specific settings – for example uterus, endometrium or the ovary in gynaecology and similar options for obstetrics – which may save time when commencing the scan. Software on all ultrasound machines provides an arrow or a cursor, which is quite useful when explaining the scan findings on the screen to the patient. The tracker ball serves as a computer mouse and helps move the cursor or the measuring point.
Figure 1.2(a,b) (a) displays the mark on the left side of the screen (arrow) and the corresponding markers indicating the direction of scanning are inactive (rectangle on (b)). This is the preferred way of scanning and most of the images in this book are displayed this way. The * indicates where the bladder would be in each of the orientations.
Figure 1.2(c,d) Activating one of the buttons (highlighted green in (d), within the white box) flips the image displayed on the screen by 180 degrees. Notice the mark on the bottom left side of the screen (arrow in (c)).
Figure 1.2(e,f) Activating both markers (green within the box) flips the display by 180 degrees and changes right for left. Notice the mark on the screen (arrow in (e)).
Technique and Steps for Ultrasound Examination
It is useful to understand the movement of the transducer while performing the ultrasound examination. The probe needs to be moved from left to right, or the reverse, for longitudinal scan, and up and down for a transverse scan. Ensure that while the probe is moving the organ being scanned is kept in the centre of the field of view, otherwise the organ will move on the screen without the scan being completed. The probe needs to move from one end of the organ being scanned to the other end, and go beyond the structure so that the structure is completely lost on the screen. Repeat this process for transverse examination to avoid missing uterine malformations and subserosal fibroids.
Imagine that your palm with the fingers is the ultrasound transducer and the thumb indicates the direction. When the thumb is facing upwards, the probe is held in a longitudinal mode, and when the thumb is pointing to the right side of the patient, this constitutes the transverse mode of scanning (Figures 1.3 and 1.4). Once the structure is identified and good contact is maintained, the movement of the probe resembles the movement of the palm at the wrist joint from right to left, and the reverse, until you have completely scanned the structure in the longitudinal/sagittal plane. In the transverse mode, the palm moves at the wrist with up-and-down motions. Please note that any axial movement (rotation) of the probe will make identification of the true axis of the structure difficult and is a common mistake made by those learning to scan (an exception is scanning foetal long bones, when axial rotation of the transducer allows identification of the actual length of the bone).
(a) The palm with the thumb upwards representing the probe in a longitudinal axis; the movement of the probe is sideways at the wrist joint.
(b) Probe held correctly for a longitudinal image with thumb facing upwards.
In summary, the structure being scanned should be identified clearly, good contact with the tissue should be maintained while the scan is performed to acquire a good-quality image, and the probe should move very slowly for a thorough examination of the structure being scanned. Failure to identify the structure, or lack of good contact and axial rotation, are generally the main reasons why most beginners initially struggle to acquire good-quality images.
Transvaginal Probe and Scanning (TVS)
Once the machine has been switched on, the next step is to identify the probes attached to the machine. On the keyboard, or the panel, there will be a sign for probe selection, which will display the transducers available for use. Almost all machines will have a two-dimensional (2D) transvaginal and a 2D abdominal transducer for gynaecology scanning. Three-dimensional (3D) probes are provided separately and are much bulkier in appearance, especially the abdominal transducer. When changing probes, it may be necessary to press the freeze button to activate the transducer. If selecting the transvaginal probe, a semicircle image will appear on the screen. This semicircle is the active part of a TVS image measuring to an angle of up to 180 degrees (scanning angle), which can be adjusted. A wider angle allows for an overview of the structures of interest and the surrounding tissues, whereas a narrow angle allows one to focus on a specific area. This is especially important when assessing moving objects, particularly the foetal heartbeat in early gestation, as a wide angle has a low screen refresh rate (measured in hertz (Hz) and displayed on the screen); narrowing the angle allows for a faster screen refresh and better identification of foetal heartbeat. An abdominal probe has a curvilinear image appearance with a slight curvature representing the probe surface. Thus, by just looking at the screen one can identify which probe is being used, and probes may be changed as appropriate.
Holding the Probe
The first step to correctly hold the probe is to identify either a groove or a depression on the probe handle. While doing a TVS, the thumb should be placed on the depression or the groove of the transducer (Figure 1.5). Holding the probe correctly while scanning is an important step. Scanning with the thumb facing upwards allows you to perform longitudinal imaging (Figure 1.3) and with the thumb placed to the right of the patient allows transverse imaging of the structure being scanned (Figure 1.4). Scanning with the thumb facing to the left of the patient or downward may lead to mistakes related to location of structures (Figure 1.6). Aligning the top and bottom and the right and left sides of the image on the screen is the next important step. The image on the screen shows a mark (this could be the logo of the scan machine company) identifying the ‘right’ in a transversely held probe and ‘top’ in a longitudinally held probe (Figure 1.7). This mark can be reversed or inverted by pressing appropriate buttons on the keyboard (Figure 1.2). A very important point to remember for all who are learning to scan is to follow one particular system while scanning. Ensure the mark is in the same position on every occasion that one performs scans by making appropriate adjustments on the keyboard with the invert and right/left buttons. For consistency, all descriptions in this chapter assume the mark to be on the top and the left side of the screen (Figure 1.2a). Whatever the preferred settings are, these need to be changed accordingly before scanning is commenced.
(a) The thumb should be placed on the groove (arrow) of the TVS probe.
(b) When ultrasound gel is applied to the surface of the transducer on the side where the groove is (arrow), the corresponding image displayed on the screen displays the mark on the left side of the screen. This is the preferred way of scanning and most of the images in this book are displayed in this way. The * indicates where the bladder would be in each of the orientations.
Figure 1.6 Thumb facing the left side or downwards should never be the position of the probe while doing TVS scanning.
In the image on the screen, the right and top are aligned with the patient’s (and not the scanner’s) right; making a note of this is very useful to avoid a basic error of sides and position (right- or left-sided ovarian cyst or a breech/cephalic presentation in an abdominal scan). A good way of demonstrating this is to hold the probe as in a longitudinal scan (thumb is placed up as in Figure 1.2) and then if you place a small amount of gel on the top of the probe before the probe is inserted into the vagina the screen will show the structure; in this situation ‘the gel’ is on the left side of the screen (Figure 1.5). Any part of the scanned organ that appears on the left side of the screen in a longitudinal view is cranial in an abdominal scan and top (anterior) in a transvaginal scan, and on the right half of the screen is caudal (posterior in a TVS). For example, in an anteverted uterus on a longitudinal scan the fundus will be on the left side when looking at the screen and the cervix on the right when looking at the screen, whereas in a retroverted uterus it is the reverse, i.e. the cervix appears on the left side of the screen and the fundus on the right (Figure 1.7).
