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5+ Reasons Why You Shouldn't Empty Your Bladder Before An Ultrasound

by David Smith

| Updated October 25, 2023 |
So, you have an ultrasound appointment coming up, and you have this persistent question running through your mind: To empty or not to empty your bladder when preparing for an ultrasound?

The answer?

Renal and pelvic ultrasounds that scan your urinary and reproductive organs provide more accurate results when done with a full bladder. As such, you should not empty your bladder before a bladder or pelvic ultrasound.

But that’s a rather generic answer. So, let’s make it more specific in the rest of the article. To begin with, the reason why you should have a full bladder before an ultrasound has to do with the working of the ultrasound machine. Let’s start there!

1.How Do Ultrasound Machines Work? 

Ultrasounds are generally 2-part machines. They have a probe (transducer) and a processor or a kind of computer.

During the imaging process, the ultrasound probe produces sound waves and directs them to body organs. When these sound waves hit the body organs, they echo back to the probe. The probe then sends them to the processor for interpretation. Lastly, the sonographer can see the interpreted waves as images on the monitor.

To do all this, the probe ultrasound waves must be able to penetrate through the skin and body organs. And that’s where a full bladder before an ultrasound comes in.

2.Why You Shouldn’t Empty Your Bladder When Preparing for an Ultrasound

There are 5 reasons why it is important to have a full bladder for an ultrasound and why you should not empty your bladder when preparing for an ultrasound.

1.A Full Bladder Clears the Way for Ultrasound Waves

A large urine volume causes bladder distention or enlargement. Under normal circumstances, a distended bladder is not a healthy situation. But, for ultrasound scanning, an enlarged full bladder helps produce a clear ultrasound image.
That’s because the enlarged bladder pushes the bowels and other pelvic organs out of the way of ultrasound waves. As such, the waves are transmitted directly to the targeted organs, bringing back precise and clear ultrasound images.

2.Ultrasound Waves Travel Better Through Fluid

Fluid has a higher wave transmission speed and intensity than soft tissue. That explains why ultrasound waves move to and return from the organs faster through a fluid-filled bladder. Also, the fast speed of ultrasound waves through bladder fluid facilitates higher wave intensity.

As a result, the image produced is high-quality, better than what would be if the ultrasound waves had to navigate through dense body tissues.

It's worth noting that the speed of ultrasound waves through a fluid also depends on the probe frequency. For example, portable ultrasound machines have a 2Mhz probe frequency. This frequency can be higher in high-tech brands like the BladGo 2.0, which has a 2.5 MHz probe frequency and produces high-quality images.

3.A Full Bladder Acts as Good Sound Medium

To be transmitted, sound needs a medium to travel through. The medium should have enough density but not too heavy. Gas has little density compared to liquids and solids. So, between urine, body tissues, and gas, body tissues are too dense, gas has insufficient density, while urine (fluid) has the appropriate density for ultrasound wave transmission.

Luckily, gas is not a natural occurrence in the bladder. It only happens with bladder infections and inflammations, as in the case of cystitis. However, having a full bladder before a scan will eliminate the gas in these cases and aid the transmission of ultrasound waves.

4.A Full Bladder has Clearer Urine for Better Visualization

Drinking a lot of water makes your urine clear. When you fill your bladder to prepare for an ultrasound by drinking plenty of water, you create a clear fluid through which the sonographer can clearly see the bladder, its contents, and the organs in the pelvic area.
As a result, the sonographer can position the ultrasound probe in the best spot for a clear image. And that also means precise interpretation of the ultrasound image and proper diagnosis.

Most healthcare practitioners will tell you to drink 1 liter (around 32 ounces) of water before the ultrasound. They will also advise you to empty your bladder 2-3 hours before the ultrasound so you can fill it again for the scan.

5.An Empty Bladder Makes Space for Solid Body Tissue

When you empty your bladder, it shrinks to its usual size. That causes two things to happen:

●The bladder presents as a solid pouch of tissue.
●The pelvic organs around the bladder take up the freed space.

When you take an ultrasound with an empty bladder, the soundwaves will be working with solid body tissues, which are denser. That means poor soundwave transmission and, consequently, a poor ultrasound image.

3. Summing It Up!

Ever wondered what happens if you empty your bladder before an ultrasound? Well, the empty bladder blocks the movement and intensity of ultrasound waves. As a result, the ultrasound image is not of the best quality.

You don’t want your ultrasound scan to be poor quality, right? Then don’t empty your bladder when preparing for an ultrasound. If you do, you’ll have to wait longer at your appointment while drinking more water to fill your bladder.
Article by
David Smith
David is a urologist with over 9 years of experience. He is also the Co-fonder of BladGo, where he regularly shares his expertise in the field of urology. David is committed to keeping readers up-to-date on the latest urological research and to sharing other beneficial healthcare tips and information so that they can live healthier lives.

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