Transvaginal ScanCHAPTER 1

Evaluation of the female genital tract is the chief diagnostic modality for any gynecological disease and basis of success of any assisted reproductive technology (ART). Ultrasound (US) is the most convenient and reliable modality for evaluation of uterus, fallopian tubes and ovaries. Though these pelvic organs can be assessed by transabdominal, transrectal and transvaginal US; transvaginal route gives best visibility and accuracy of diagnosis.

This is so because

At least a verbal consent of the patient is essential. Patient is asked to empty the bladder. Patient is undressed, placed in lithotomy like position (Figure 2) on the gynecology couch in the same way as for per speculum or per vaginal examination and is adequately covered with a clean sheet, so that she does not feel uncomfortable. Maintaining privacy and dignity of the patient is of utmost importance. Gynecology couch, as it has a gap in the center, allows easy probe movements (Figure 3). A pillow under the patient's buttocks may help, to raise the buttocks if the scan is done on flat bed. Ultrasound jelly is put on the head of the transvaginal probe and then the probe is covered with the condom, not leaving any air between the probe and the condom.

A small amount of jelly is then placed over the condom on the probe head and the probe is gently slided into the patient's vagina. (Figure 4). Counseling the patient before examination and explaining the whole procedure, helps eliminate the anxiety and resistance.

In case of difficulty in introduction or patient's resistance to introduction, she is advised to take deep long breaths with open mouth, i.e. deep inspirations and long complete expirations. In spite of that if introduction of probe is difficult, the pressure should be exerted posteriorly towards the rectum which will make introduction of the probe into the vagina easier.

There are basic four types of probe movements used for transvaginal scan.

It is used at the probe entry and exit from the vagina. This movement helps to slide the tissue planes over one another. (Video 1). It is used to diagnose adhesions between uterus and ovaries, ovaries or uterus with bowels loops or anterior and posterior vaginal walls with bladder wall or rectal wall.

This is moving the probe from right side of the patient to the left side of the patient or vice versa, without rotation.

But spanning may be done with the probe in rotated in any direction (Video 2). It is used for the survey of anatomy of the pelvis.

Rotation movement of the probe does not include movement of the probe position. It is only clockwise or anticlockwise rotation of the probe. This movement is used to visualize a particular organ or lesion in different axis. Rotation of the probe can be done in clockwise or anticlockwise direction (Video 3).

This is only angulating the probe towards roof or floor, i.e. is patient's anterior or posterior aspect. Moving the handle up, directs the probe head down (posterior aspect of patient) and moving the handle down, directs the probe head up (towards patient's anterior aspect). This movement along with the spanning movement is used for survey of the anatomy and to find out the position of structure or an organ (Video 4 probe movement).

Usually, there are presets on all ultrasound equipments for different scans and there is one for each scan and there is one for gynecological 5scans also. The advantage of using a good and proper preset is that one has to manipulate the equipment settings minimally and still get good quality images with majority of the scans. A good quality B mode image is a primary requirement for good quality color Doppler, volume ultrasound images and over and above all for correct diagnosis. Though most of the times, the presets work well, several parameters need to be adjusted with each patient, due to variations in physique, habitus and anatomy. Even if the physics part of it is omitted, it is essential to know about the knobs, what do they do and when to use them.

Each probe has a maximum scanning angle. This is the maximum angle upto which the ultrasound beam can fan out. It indicates as to how much area can be covered by a single ultrasound beam or how much sidewards can an ultrasound beam see. Maximum scanning angle for transvaginal probes usually vary from 80°–180°. Large scanning angle is very convenient for obtaining the bird's eye view of the pelvis, (Figure 9) but it decreases the speed of scanning which is indicated by frame rate.

It is known that the real time B mode images that we are seeing on the scanner screen appear continuous because of several static images seen quickly one after the other. Faster the change in frames more real time it looks. Frame rate is the number of static images captured in a unit time by the scanner. This means that if the frame rate is low the image resolution is low, it appears less clear and reveals fewer details. Therefore, once the area of interest has been located, the scanning angle should to narrowed down to just a little larger than the area of interest. Narrowing the scanning angle frame rate, and therefore results in better resolution image (Figure 10).

Each probe has a limit of maximum depth upto which the ultrasound beam can penetrate. This of course depends on frequency of the sound wave. Low frequency sound wave can penetrate deeper and high frequency sound wave can penetrate shallow depths. Maximum achievable depth by any probe may be used for the initial survey, but then depending on the depth at which the area of interest is, the scanning depth can be decreased. This maneuver again increases the frame rate and therefore improves resolution (Figures 11A and B).

As discussed earlier lower frequency ultrasound has higher penetration capacity, but has lower resolution, whereas higher frequency sound beam has less lower depth penetration but higher resolution. The transvaginal probes available now are multifrequency probes and one can select the frequency depending on the depth penetration required. The options present on the scanner may be high, medium or low frequency or adipose, normal and penetration setting (Figures 12A and B). Commonly available probes are 5–9 MHz and 6–12 MHz.

The ultrasound beam behaves like a light wave passing through the convex lens and therefore concentrates at a plane called focal zone. Focal zone is the level at which the image is the sharpest. Therefore, focal zone is always set at the level of area of interest. The arrow head on right side of the image indicates the focal zone. There is also an option of having more than one focal zone, when there are multiple levels at which the image needs to be sharp. But increasing the number of focal zones, decreases the frame rate and therefore usually single focal zone is selected (Figure 13).

After the overview scanning and decreasing the scanning angle and depth, further improvement in the image quality can be achieved by zooming the image. One may zoom the whole image (Pan-zoom) or may use a zooming box to decide and define which part of the image needs zooming (HD zoom). Panzoom only enlarges the image and therefore increases the distance between the image pixels and deteriorates the image quality (Figures 14A and B).

Whereas HD zoom concentrates pixels into a smaller box and thus improves image resolution. Larger image can depict more anatomical details and also results in smaller human errors when measurements are done (Figure 15). Image should be zoomed large enough to fill up at least 3/4th of the screen.

The ultrasound wave when emitted from the probe into the body, it hits several tissue planes on its onwards as well as return path. With each plane that it crosses, i.e. that is with the distance that it traverses, it attenuates. This leads to darker (hypoechoic) image of the structures far from the probe than what they are and this may 8cause an error of diagnosis.

A solid structure may appear cystic. Image can be made brighter by increasing the gains. This is strengthening of the returning beam to make the image brighter. But changing gains inadvertently may lead to erroneous diagnosis. Therefore in all doubtful, difficult situations, the gains are set in such a way that the urinary bladder appears anechoic and echogenicity of other structures are assessed in relation to bladder. (Figures 16A and B) (Video 5). Gains can be adjusted in two ways. Total gains can be increased/decreased or gains can be adjusted layer wise, depending on the distance of the tissue plane from the probe. The later one is known as TGC (time gain compensation). Ultrasound wave returning from deeper structures takes longer time to return and is attenuated. This control compensates for the gains lost by time. (Video 6)

Brightness of the image can also be adjusted by increasing the power of the incident beam. Gain adjustment corrects the returning beam and power affects the incident beam. Probe power can be increased maximum to 100%, but usually set at between 80–90%. This decreases the total mechanical and thermal energy transmitted to the tissues. (Figure 17).

Increased contrast means more black and white image with less shades of gray, and less contrast means more shades of gray in an image. High contrast (Figure 18A) may therefore hide the details of soft tissues and so is usually selected for study of cystic structures or bones. Low contrast (Figure 18B) may mask calcifications. Contrast setting (Figure 18C) may also be presented as dynamic contrast on the ultrasound machine.

Probe is introduced in the longitudinal position. That is the position in which the indicators (arrow) on the probe remain up, facing the roof of the room, that is on anterior aspect of the patient (Figure 19). These indicators on the probe match the indicator (logo of the company-circle on the screen (Figure 20). This means that if the indicator on the screen is on the right side of the screen, the structures anteriorly placed are on the right side of the screen and vice a versa. Uterus is normally seen in the midline with this probe position. If uterus is not seen, in the center, the probe is spanned from one side in the pelvis to the other side to search for the uterus. Once the uterus is located with the probe in the same position (without rotation), it is spanned from right to left side of the patient, scanning the uterus in long axis from one side to other (Video 7).

Locate and assess the ovary in a true transverse section and then rotate it 90° 10to get a true long axis of the ovary, the largest longitudinal diameter (Video 10).

Assess the ovaries for any pathology (Video 11). Then span the probe, come back to the midline and follow the same procedure for the opposite adnexa. In and out movement of the probe with the ovary in view or pressing from the abdomen when probe is looking at the ovary and checking the sliding of the organs against each other confirms mobility of the ovaries and rules out adhesions (Videos 12 and 13). This is also known as Timor-Trsitch sign or a sliding organ sign.

When sound is reflected from a moving object the returning wave has a different frequency than the transmitted frequency, which is known as Doppler shift. The frequency is more than the transmitted frequency when the object moves towards the probe and is less if the object is moving away from the probe.

The physics and facts of different types of Doppler used for diagnosis is complicated and therefore we shall here discuss only the practically relevant points.

This is a semiquantitative directional Doppler. Flow towards the probe appears red and flow away from the probe appears blue (Figure 27). The brightness of the color represents the intensity of the flow.

This is a nondirectional Doppler. Any moving object represents color (Figure 28).

This is a directional quantitative Doppler. The flow signals are marked as a spectrum. Flow towards the probe is seen above the baseline and flow away from the probe is seen below the baseline. The height of the signal from the baseline on the spectrum can be measured and represents the velocity of the flow.

To derive the correct information about the flows, it is important to set the Doppler parameters. These settings are as follows:

Same as for B-mode scan, size of color box should be kept to the smallest possible to get highest frame rates (Figures 30A and B).

Higher pulse repetition frequency is to be selected for interrogation of blood flows with high velocity and lower PRF for blood flows with lower velocity (Figures 31A and B). Selecting high PRF for low velocity flows lead to elimination of flow information and selecting low PRF for high velocity flows leads to artifact called aliasing.

As is known, Doppler is a frequency shift arising due to movement of the target object and with other variables, its amplitude also depends on velocity of the target object. This means that when moving RBCs (red blood cells) are producing high amplitude signals, vessel wall that moves much slower than 14RBCs also produce low amplitude signals.

These signals do not produce any useful information and so should be best filtered out. This function is done by wall filter. It restricts low amplitude signals to improve the quality of signals coming from blood flows. Wall filter is set to lowest for low velocity blood flows like follicular or endometrial flows. If the wall filter is high it would cut down the information of the diastolic flow first and also sometimes the information from low velocity systolic flow (Figures 32A and B). For study of very high velocity blood flows like in fetal echocardiography, the amplitude of movement of heart wall is also high and so wall filter setting is also adjusted to high, otherwise there will be lot of noise and the information of blood flows will be polluted.

Gains, like in B-mode settings must be set correctly for color Doppler also. Too much gains leads to spill of color outside the vessels and too little gains leads to cutting off the information of low velocity flows (Figures 33A to C). In any vessel, the blood flow velocity 15is highest in the center, but is low close to the walls, due to friction with the wall.

It is information about this flow that may be missed by low gains or high wall filter. The image of color Doppler in that case would show gap between vessel wall and color column.

This is an important setting. Even with all above mentioned settings, the color filling is dependent on the brightness of B-mode image. The color appears patchy when the B-mode image is too bright. The limit of brightness beyond which the color will appear patchy is decided by balance. On the left upper corner of the screen, two vertical bands are seen, one in gray and one in color. On the gray band, a green line is seen which indicates the balance.

If the brightness of the image is more than the brightness above the green line, the color filling will appear patchy. To correct this either the gains on B-mode are decreased or the 16balance is to be increased. Generally therefore, if this manipulation with every patient is to be avoided, the balance is to be set in such a way that the B-mode image does not become too dark and the color fill up is smooth (Figures 34A and B).

The sample volume should be equal to the diameter of the vessel. If large may lead to overlapping of spectrum from multiple vessels and if small may evaluate flow only in part of the vessel lumen (Figures 35A and B).

This is a very important setting for velocity assessments. It has been described earlier in the equation for Doppler shift, that the shift is dependent on cos θ where θ is the Doppler angle. Because value of cos 0° is one and that of cos 90° is 0, the correct value of velocities can be achieved when the Doppler angle is the smallest. As the Doppler angle increases the error in velocity calculation increases, till it becomes unacceptable beyond 60°. Therefore, Doppler angle should be set at the lowest possible. When spectral Doppler is switched on, a dotted line appears appears on the screen, on which a sample volume appears and also a line that can be rotated. The angle formed between this line and the dotted line indicates the Doppler angle. This line should be adjusted in such a way that it remains as parallel to the vessel as possible and the Doppler angle is the smallest possible. (Figures 36A to C).

Gains should be adjusted in such a way that the spectrum appears clear—only the information of the flow is seen and no information of the flow is being eliminated from the spectrum. Too high gains create noise (unwanted movement information), too low gains eliminate the signals from low-diastolic flow (Figures 37A to C).

Mirror image artifact 18(Figure 41) is seen on spectral Doppler and can be avoided by selecting a correct sample volume to avoid interrogating two loops of a vessel or two vessels at a time. Other instant when a mirror image artifact is seen is when a large sample volume is placed on the curved vessel.

It is out of the scope of this book to explain the basics of 3D ultrasound and all the applications of volume ultrasound as such. We shall therefore discuss only the relevant applications of volume ultrasound here. Volume ultrasound combined with transvaginal scan has revolutionized the gynecological imaging. Multiple planes and sections available on the tissue blocks of volume ultrasound has made the understanding of the complex anatomy easy. The availability of coronal section is of prime importance. Volume ultrasound has also made volume calculations more accurate.

This is of importance for gynecological masses as well as for infertility assessment. New softwares of volume calculation like SonoAVC have great applicabilities in infertility for follicular assessment as well as for other fluid filled masses of fallopian tubes or ovaries and also for volumetric assessment of early pregnancy. New rendering mode—HD Live is very helpful for assessment of uterus, for HyCoSy and for assessment of fetal development.

The area of interest is first selected on the B-mode scan. This area should ideally be placed in the center of the monitor screen. The B-mode image should be optimized. The volume box is switched on and is placed over the area of interest. The volume box should be large enough to include the area of interest with at least 5–10 mm of margin on all sides. To select the volume angle, probe is manually angulated up and down or side to side depending on orientation of the image to assess the depth the organ of interest. Quality of the volume is selected depending on whether the structure or organ of interest is steady and stable or has movements. Higher quality takes longer to acquire as it contains more B-mode images in the volume block, whereas lower quality images takes shorter time to acquire. Having adjusted the region/area of interest, angle of acquisition and quality, then acquisition is done. The transducer head takes an automatic sweep and the acquired volume is displayed on the screen as three images in three orthogonal planes—x, y, z axis.

Walking through each image would take through the complete anatomical details in the volume box in individual plane. This is multiplanar imaging. This is the study of sectional planes and makes the understanding of anatomical relationship of various structures clear. A dot is seen in each image and this is the point at which the orthogonal planes intersect. This point is known as the reference point as it represents the same anatomical landmark in all three sections. Coronal section is the most important, as this is the plane which is inaccessible on B-mode ultrasound imaging (Figure 42).

Viewing the whole tissue block as a whole from any one side is known as rendering (Figure 43). When the image is rendered a box appears on each image. In two of the three images, the box is drawn by three yellow lines and one green line and in the third image, the box has all yellow lines. The resulting rendered image will be similar to the image in this later box. The green line on the box is the viewing line. This line is aligned with the curve of the organ of interest. For gynecological scans and infertility scans almost always up-down rendering direction is used. Rendering can be done in various modes and even combination of various rendering modes can be used viz. Surface modes, transparent modes, inversion, angiomode, etc. (Figures 44A to D). For tissue rendering that is required for uterus and ovaries commonly combination of surface texture or smooth with transparent mode is used. Though rendering can be done for straight as well as curved surfaces, it is difficult to render the uterus or any other surfaces with acute curves. It is in these cases that omniview is used (Figure 45).

For 3D power Doppler angiographies, the acquisition is done with power Doppler and rendering is done in glassbody or angiomode (Figures 46A and B) to 22see the soft tissue details and vascular anatomy together or only blood vessels respectively. Using volume histogram with the volume that is acquired with power Doppler, allows quanitative assessment of the global vascular indices..

It is therefore of great help for calculation of antral follicles or for calculation of follicular diameter or volume or multiple pre-hCG follicles of controlled ovarian hyperstimulation (Figure 50). SonoAVC can also be used for volume calculation of hydrosalpinx, cystic adnexal lesions or early gestational sac (Figures 51A and B).

Adjust angle, focal zones, focal depth, contrast (Dynamic range), gains, zoom probe power, probe frequency.

Size of color box or sample volume, gains, PRF, wall filter, probe power, Doppler angle.

Multiplanar imaging, omniview, VCI, TUI, rendering, VOCAL and SonoAVC.