Why Full Blader Ultrasound
This is a common phrase from the receptionist whenever one books for a pregnancy or gynaecological ultrasound examination. What is the medical science behind this simple but sometimes uncomfortable request?
How ultrasound machines function:
Ultrasound equipment generates and receives sound waves. Ultrasound waves are at very high frequency that can’t be heard by the human ear. Once the ultrasound probe is placed on or in your body, it transmits sound waves through your body. The sound waves travel through your body to organs and structures along their path of transmission. Sound energy and light energy have lots of similarities. Both can be reflected and in the case of sound, giving an echo as a result or it can be refracted leading to a change in transmission path.
Sound waves which are reflected or bounced back (echo) are very important in ultrasound examinations. We rely on the echo to make a diagnosis. The ultrasound machine can amplify and process these echoes and by using a special computer can generate an image of the body part that is getting scanned on a video screen which can be saved e.g. baby parts, uterus, ovaries etc. Once the computer has assessed these echoes it is possible to determine the distance, size, shape and consistency of the target organ.
What is the Advantage of a Full Bladder:
The primary objective of every examination is to transmit as much sound energy as one can, so that we receive a good echo which may lead to better images. The use of ultrasound gel helps to maximise transmission of sound. Body tissues or organs have their own different inherent tendencies to sound transmission. Fluid filled body cavities have good transmission of sound whereas gas filled organs e.g. bowel and lungs have poor transmission of sound. In fluid filled cavities, there is better transmission and good echoes and in gas filled organs there is poor transmission and weak echoes.
A full bladder helps the sonographer in several ways:
Sound transmitted through the bladder results in more sound energy at the target organs e.g. baby, cervix, uterus ovaries etc. This results in good echoes and better, more crisp images on display as the round trip of sound energy has little resistance to transmission.
Air is a very strong ultrasound beam reflector. Bowel tends to fill up with intestinal contents and gas. This makes it almost impossible to get good transmission of sound to target organs if bowel is along the pathway as almost all the sound will get reflected before reaching the region of interest. A full bladder helps by pushing bowel out of the pelvis allowing transmission of ultrasound to target organs.
Most women have an anteverted (tilted forwards) womb which unfortunately in some cases doesn’t present the ideal angle to the sound transmission pathway. A full bladder tilts the womb backwards hence presenting a more favourable angle to the transmitted sound energy which results in better images.
How much fluid should one take:
Bladder capacity and behaviour varies with individuals. Ideally, drink as much fluid to make your bladder comfortably full. If your bladder is not adequately full or is very full and causing great discomfort, both may impact negatively on the examination.
Depending on the service provider you may not need a full bladder for all examinations. Most early pregnancy ultrasound scans and up to 22-24 weeks will need a full bladder but thereafter possibly not. Gynaecological scans performed using the vaginal approach generally don’t need a full bladder as the ultrasound probe is much closer to the region of interest. When booking for an ultrasound scan, the reception staff will advise you accordingly depending on the indication for the scan on your referral.
Why You Shouldn’t Empty Your Bladder When Preparing for an Ultrasound
The answer is simple: one of the most common areas on the body to be examined through an ultrasound scan is the abdomen. Depending on the internal structure that is to be scanned, the bladder may need to be full for better visualization. This is because of the nature of sound waves and the way they move though different mediums such as air or fluids. If you have ever had your head underwater, you may have noticed that sounds are more muffled.
In the same way, your bladder acts as a reservoir of fluid, which helps the sound waves bounce back for better visibility and more detailed images. In such cases, you should not empty your bladder, because the extra fluid is necessary for the ultrasound.
Not every ultrasound requires a full bladder. It really depends on the specific body area being imaged. Fluid can increase visibility in some cases, but it can also obstruct the view of some internal structures. There are only a few ultrasound scans that require you to have a full bladder, and your doctor will inform you when the time comes if yours should be full or empty.
Full or Empty Bladder Ultrasound Scans:
Pregnancy Ultrasound (in early stages) – If the pregnancy is in the early stages, before the 20th to 24th week, then it is necessary to have a full bladder for an ultrasound. This is needed to provide better visualization of the pelvic organs. In the later stages of pregnancy, the fetus moves from the pelvis and is surrounded by amniotic fluid, which serves as a medium for visualization, and it’s no longer necessary to have a full bladder. In fact, in this case, a full bladder may distort the imaging.
KUB Ultrasound – KUB (Renal Ultrasound) is used to evaluate the urinary tract, including the kidneys, urinary bladder (and ureters if female, the prostate gland and seminal vesicles if the patient is male). KUB ultrasound is used to observe if there are changes in the kidneys that can point to signs of damage, structural abnormalities, and even the presence of kidney stones, tumors, or cysts. Patient must often drink a liter of water one hour before the ultrasound is performed. In this case, the full bladder is necessary to evaluate the urinary bladder properly as the bladder volume will be measured during the scan.
Transvaginal Ultrasound – Transvaginal ultrasound uses an ultrasound probe or transducer that is inserted into the vagina. The transvaginal ultrasound is used to view female reproductive organs like the uterus, cervix, and ovaries. Although the transvaginal ultrasound can be used during pregnancy to view the placenta or monitor fetal growth in the early stages of pregnancy, it is also used to diagnose ectopic pregnancy, fibroid tumors, and cysts. It can also be used to evaluate infertility, menstrual problems, or pelvic pain. A full bladder in this case would not only distort the image of the uterus but it will also be uncomfortable for the woman. The bladder for this ultrasound needs to be empty.
An empty or full bladder can mean the difference in how accurate the ultrasound imaging is. Knowing what imaging procedure you are scheduled for can determine whether or not you need to have an empty or full bladder.
If you, or a loved one needs an ultrasound scan, or any other imaging services, or if you would like to schedule an appointment for an ultrasound examination, please call 561-795-5558 today, or go online to make an appointment. Our board-certified radiologists are right here in the Lake Worth, Wellington, Belle Glade, or Royal Palm Beach areas.
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