Ultrasound in Medicine Standard Grade Physics Health Physics Click here to go to the menu

Ultrasound in Medicine This presentation will explain what ultrasound is and how it is used in medicine. You will be given a choice of general or credit options, ask your teacher which you should take. Always follow the instructions on screen!

What is Ultrasound? Ultrasound is simply sound that has a very high frequency. Humans are not able to hear ultrasound, though some animals can hear them. Sounds with frequencies above hertz are called ultrasounds.

Uses of Ultrasound in Medicine Ultrasound is used for examining soft tissue inside the body. Parts of the body that may be examined include muscles and unborn babies. Blood flow can also be monitored using ultrasound. © 2000 ATL Ultrasound Ultrasound images courtesy of ATL

The Power of Ultrasound Modern ultrasound equipment can produce 3D images Colour enhancement to show blood flow Digital files for examination on computers © 2000 ATL Ultrasound Ultrasound images courtesy of ATL

Aaah, How Cute! The images so far have been of static images, ultrasound captures movement. This baby is so pleased to see you its waving! You can see more images at come1.htm (but youll need an internet connection to get there!) come1.htm © 2000 ATL Ultrasound Ultrasound images courtesy of ATL

Why Use Ultrasound? Ultrasound is very safe. There is no firm evidence that it does any harm to the body (or the baby in the case of pregnancy scans). X-rays are potentially dangerous, particularly to young children and pregnant women (they damage the unborn baby).

How Does It Work? Medical ultrasound systems use very high frequencies - several megahertz (mega means million or 10 6 ). A sound is a wave it has all the usual wave properties (reflection, refraction, diffraction). Ultrasound imaging makes use of the fact that sound can be reflected. The idea is just like that used in radar and sonar.

More about how it works… The probe contains a transmitter and a receiver. A pulse of ultrasound is sent out by the transmitter. The pulse is reflected from a surface and returns to the receiver. The ultrasound machine measures how long it takes for the pulse to return Ultrasound probe Body tissue (muscle etc) skin A thin layer of jelly is placed between the probe and the skin to make sure all the sound enters the body.

How the image is created… Millions of sound waves are transmitted every second. As the waves reflected at different times, the computer in the ultrasound machine calculates how far the wave travelled before being reflected (using d=vt). Using this information the computer builds up an image of the inside of the patient. © 2000 ATL Ultrasound Ultrasound images courtesy of ATL

Menu: Please make a choice Re-run the presentation Starter questions General questions Credit questions Problem solving strategies

Starter Questions 1. What is ultrasound? 2. What can ultrasound be used for? 3. Which of these frequencies are ultrasound frequencies? Hz Hz15.1 kHz36 kHz 4 MHz0.58 MHz Hz Hz 4. What advantages does ultrasound have over x-rays for examining inside the body? Answer all question in sentences. If you are stuck, look back through the presentation. Press a key to go to the next question. Click here to return to the menu

Answers to Starter Questions 1. Ultrasound is sound with a frequency above Hz. If you have just said that it is a sound we cannot hear, that is not quite accurate enough. 2. Ultrasound can be used for examining soft tissue inside the body. For example, muscle, the heart and unborn babies. 3. The following are ultrasound frequencies: Hz, 36 kHz, 4 MHz, 0.58 MHz, Hz 4. Ultrasound does not have any damaging effect on the body. It is entirely safe to use, even on very young foetuses. X-rays are harmful, particularly on young and unborn children. Click here to return to the menu Please return to the main menu and select credit or general questions Click here to return to the menu

Problem Solving Strategies Most of the problems involving ultrasound need you to use v=d/t or v=f Things to look out for: – Units- time will often be in milliseconds (ms). Take care not to get this confused with metres per second (m/s or ms -1). and distances may be in mm or cm There will often be an echo (or reflection involved. This means that you will need to think carefully about the times and distances involved. The following worked examples should help you. Click here to return to the menu

Example Problems There are several example questions. You can either work through all of them, or choose the ones you want to look at. Click here to return to the menu Changing units Reflections

Basic Question Example 1 The speed of sound in human tissue is 1500m/s. How long will it take for a sound wave to reach a muscle 4 cm below the surface of the skin? Press a key to go through the worked example Things to look out for…units! summarise the information: v = 1500 m/s d= 4 cm (…units!) = 0.04 m t = ? choose your equation t=d/v substitute in your numbers t = 0.04/1500 t= s change to standard form t = 2.67 x s (dont forget your units) Click here to return to the menu

Basic Question Example 2 How deep is a babys head if it takes ms for a sound wave to reach it in the mothers womb? The speed of sound in body tissue is 1500 m/s. Press a key to go through the worked example Things to look out for…units! summarise the information: v = 1500 m/s d= ? t = 0.05 ms (units!) = x s choose your equation d=vt substitute in your numbers d = 1500 x 0.05 x d= m (dont forget your units) Click here to return to the menu Click here to return to the problem menu

Questions involving reflections The thing you must remember in these is that the sound has to make a round trip. The sound must travel to the baby from the transmitter. The sound must then travel back to the transmitter from the baby. If the baby is 7 cm below the skin, this means the total distance travelled is 14 cm. You must remember to take the total distance into account! Click here to return to the menu

Questions involving reflections 1 The speed of sound in the human body is 1500 m/s. If a foetus is 6 cm below the mothers skin, how long will it take for the echo to be received? Click here to return to the menu summarise the information v = 1500 m/s d = 6cm (change units and double the distance) d= 0.12 m t = ? choose your equation t = d/v substitute in your numbers t = 0.12/1500 t = s change to standard form t = 8 x s

Questions involving reflections 2 It take 0.2 ms for the sound from ultrasound probe to travel to a babys heel and back again. If sound travels at 1500 m/s inside the body, how far is the babys foot below the mothers skin? Click here to return to the menu summarise the information v = 1500 m/s d = ? t = 0.2 ms (change units and halve the time) t = s choose your equation d = vt substitute in your numbers d = 1500 x d = 0.15 m Click here to return to the menu

General Questions 1 Show all your working and include units in your answers. If you are stuck, look back at the worked examples. 1. If the speed of sound in the human body is 1500 m/s, how long will it take sound to travel 0.12 m? 2. Medical ultrasound uses frequencies of MHz. Write this frequency in hertz using standard form. 3. Change 2.3 ms to seconds. 4. How far would an ultrasound wave travel in 2.3 ms if it has a speed of 1500 ms? 5. A sound wave travelled 8 cm through bone in 0.04 ms. How fast was the wave travelling? Click here to return to the menu Click here to get the answers!

General Answers 1 Check your answers. If you have got any wrong, ask your teacher for help s (0.08 ms) x 10 8 Hz (or x 10 6 Hz…but this isnt quite as good) m m/s Click here to return to the menu Click here to go to the next set of general questions

General Questions 2 Show all your working and include units in your answers. If you are stuck, look back at the worked examples. These questions use v=f. 1. What is the wavelength of an ultrasound wave if it has a frequency of Hz and is travelling with a speed of 1500 m/s? 2. When checking a patient for a muscle injury, sound with a wavelength of m is used. If the frequency of the sound was 2 MHz, find the speed of the sound in the body. 3. A dog whistle emits ultrasound. If the speed of sound in air is 330 m/s and the sound has a wavelength of 1.1 mm, find the frequency of the dog whistle. Click here to return to the menu Click here to get the answers!

General Answers 2 Check your answers. If you have got any wrong, ask your teacher for help m m/s Hz Click here to return to the menu

Credit Questions Show all your working and include units in your answers. If you are stuck, look back at the worked examples 1. When examining a 20 week old baby, an ultrasound pulse of frequency 2.5 MHz travels 12 cm down to the babys back. The sound is travelling at 1500 m/s. a) How long will it take for the echo to return to the probe? b) What is the wavelength of the ultrasound? 2. A sound wave used to examine the bladder has a frequency of 15 MHz. The sound travels at 1500 m/s through the body. The sound travels for 0.04s before returning to the probe. a) How far below the surface of the skin is the bladder? b) Calculate the wavelength of the ultrasound. Click here to return to the menu Click here to get the answers!

Credit Answers Check your answers. If you have got any wrong, ask your teacher for help. 1. a) 0.16 ms b) 0.6 mm 2. A sound wave used to examine the bladder has a frequency of 15 MHz. The sound travels at 1500 m/s through the body. The sound travels for 0.02 ms before returning to the probe. a) 3 cm b) 0.1 mm Click here to return to the menu