Ultrasound, on the other hand (or up one peak and down the other as my Pappy used to say), operates at a much higher frequency range - between 2 and 10 MegaHertz (think of this as running at the speed of a new Ferrari). The waves pictured here will represent ultrasound.

(I let him think he's a Ferrari. Actually, he's more along the lines of one of those ancient computer chips - you remember, the original IBM AT style computers running at 6-12 MHz! Hee, hee - let's go along with his Ferrari analogy, though, it keeps his spirit up.)

If you're quite finished with my audience, we'll continue now. I want to take a side road here for a second to separate "diagnostic" ultrasound from "therapeutic" ultrasound. Diagnostic ultrasound involves low power levels and high frequencies to provide images of what's inside a body. Therapeutic ultrasound (like that in a physical therapist's office) utilizes high power levels and low frequencies to heat up tissue to encourage healing of an injured part of the body. There is no imaging with therapeutic ultrasound, and there is no tissue heating or damage with diagnostic ultrasound (see "Is Ultrasound Safe?" - just click on these words to jump if you want). So you Weekend Warriors with the sore shoulders received therapeutic ultrasound when you went to the physical therapist last week. Sure felt good, didn't it!?!

Okeedokee, let's get back to diagnostic ultrasound and how it works. Inside the probe (look at the cute picture we have for you), there is a special crystal called a "transducer." It won't channel your energy (BTW - the other ones won't either, hee, hee, they're just very organized molecules that happen to sparkle and shine - very cute, though) - but it does get affected when a tiny bit of electricity hits one side of the transducer. The ultrasound system, and all the computer circuitry inside the box, produces an electrical signal that travels down the cable to the transducer (to the probe).

The electrical signal causes the transducer to vibrate and produce sound waves in the range of ultrasound (remember - in the United States this is between 2-10 MHz - regulated by the FDA - other nations - especially in Europe - have different standards). These ultrasound waves come out of the transducer (or probe). Due to the low power levels and high frequency range, diagnostic ultrasound can't travel through air - it's too weak to do that (in fact, it's so weak you can't feel it, and the frequency is so high you can't hear it). The sonographer (that's the title of the person trained to operate and understand ultrasound systems and images - called sonograms) has to squirt some of that gel (for you biomed types, it's an acoustically designed transmission medium) onto your skin to allow the ultrasound waves to travel from the transducer, through the gel, and into your skin. Now the fun part begins.

Those ultrasound waves travel into your body and start bouncing around and off-of anything and everything inside ... except air. Once the sound waves hit air (like in your lungs, stomach, or colon) they just sort of disappear. Actually, little-by-little they sort of disappear throughout your body. It's called "attenuation" and it means that as the sound waves travel through the tissue, they lose some of their energy, becoming weaker. They end up looking like my buddy BellyWalker. (See how he's sort of "beat-up" lookin'? Don't tell him that, he's sort of sensitive about it.)

Anywhooo, they bounce around in there, getting attenuated, and some of the ultrasound waves bounce back, or echo back to the transducer. This is where we get real technical! As those ultrasound waves reach the transducer, they cause the transducer to vibrate, but this time instead of sound coming out, a small electrical signal is produced on the opposite side of the transducer! Awesome piece of work! That electrical signal travels down the cable, goes through some sort of probe-interface board, an Analag-to-Digital coverter, some software to analyze the signal (the data), and then a video section to display a real-time image of your guts on the monitor! There's a LOT more that really goes on, but this is a general explanation of how ultrasound works. (Stay tuned for the "History of Ultrasound" - if we can't find it on the Web someplace, we'll provide it for you ourselves in the near future!)

Take a look at the picture here for a visual representation of what I just explained. Cute little guy, isn't he? Or is it a "she" - you can't tell until around 15-16 weeks! Bone tissue or other dense tissue will bounce back the waves much stronger than will soft tissue or liquids (such as blood or urine). Bones will look real bright (a lot of echo) on the monitor, while liquids such as blood (in veins or arteries) or urine (in the bladder) will look almost completely black on the screen (hardly any echo). The levels of intensity of the returning sound waves are used by the system to form the picture you see. It's really quite amazing that we actually can open someone up without opening someone up!

Imaging is also improving with each year. Twenty-five years ago you could see practically nothing with the ultrasound systems of that vintage. Now you can see blood flowing through an artery and you can see the lens in an eye of a twenty-week-old baby (still inside his/her mother's belly). You can see a faulty valve in a patient's heart go flitter-flutter and you can see a tiny speck-of-a-stone in someone's gall bladder. You can see liver or kidney damage with tissue density changes and you can see an 11-week-old baby sucking his/her thumb (though the whole baby is only about two inches long!).

Due to its extreme safety in use diagnostic ultrasound is being used in many exciting ways - to assist physicians in performing fetal surgery, to help doctors correct defects in the eye, to aid the urologist in killing cancer cells in an older man's prostate without removing the organ, to give "eyes" to the specialist with a transducer on the end of a scope going down the patient's throat to take a very close look at the heart, or to determine whether pain in someone's stomach is due to endometriosis or what she ate at lunch time. The possibilities seem endless, and many new areas of usage open up continuously. All of this is done without any harm or danger to the baby in the mother's womb, to the mother (or to the kidney patient, heart patient, etc.) to the sonographer doing the scanning, to the physician standing by watching, or to the anxious dad taking the first look at his child. There has been no documented detrimental (no bad) effects from ultrasound on anyone, ever reported! (See the "Is Ultrasound Safe" section.)

Diagnostic ultrasound is one of the least expensive, safest, and most widely available modalities (or methods) of imaging inside the body to look at fluid-filled or soft tissue areas. One of the coolest things about it is that it's only sound waves! We can actually look inside someone's body with sound! Awesome!

Hey - we hope you enjoyed your little excursion into the world of diagnostic ultrasound. Try to catch us as we jump around the Initial Images web site. Hope to see you again!