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Scan line address logic?

What is meant by a computers "address logic"...and if possible the phrase "Scan line address generation logic computers". The latter is in relation to the transfer of infromation from an ultrasound beam to a computers memory. Thanks

I am NOT a computer science student. this term was mentioned in my medical physics lecture (it is a fairly basic course) so please don't make it to technical! thanks

Reply 1

Jon_6_sk

Right, I'll take a stab at this.

So, first of all scan line in case this isn't clear. I'll say the words "raster scan" and let you google it. But in the olden days, we had big box TVs, called CRTs. CRT stands for Cathode Ray Tube. Don't worry about the elements of that title, but a simple definition of how these television worked is this. The CRT shoots a beam of electrons out of the end towards the screen which is made of a material receptive to being bombarded with electrons to produce an image. But naturally, this beam of electrons is quite thin. It's not possible for this beam to be big enough to cover the whole screen and produce an image made up of many different coloured boxes in the way you expect to form an image on the screen. Instead, it flicks back and forth, row by row, shooting out electrons to the screen to construct the image. When it gets to the bottom corner, it starts again from up top. This happens 50 times per second on a CRT television. This is a rough explanation of scan lines.

For your ultrasound scanner, the same thing is true. However, instead of the scan lines generating an image, the scanner will emit a sound wave and the reflection of that soundwave is picked up. It then moves to the next pixel, throws out that base soundwave, picks up that reflection and so on. When it gets to the end of that row of pixels, it will run back and start the next row of pixels. From what I know of ultrasound, an emitter is producing some sort of base soundwave and whatever that soundwave comes into contact with reflects it in a specific way. The detector will then detect how the base soundwave has changed and that will indicate things like density at that one particular spot. This will determine how bright/dark/black/white/grey that particular spot is.

Address Generation. I assume this is referring to logical addressing and generation of. So, another quick explanation. In computing, we have simple data structures called arrays. Feel free to google it, it's probably a very basic data structure which I have picked for this explanation. Now you can imagine an array as a fixed length list of numbers. So, if you have a small sheet of notepaper, you can mark out ten lines where you can write one number on each line and that's it. That is your data structure. When you write some program code to create this array, what happens in your computer goes off and fences off some memory to store this array. It is a consecutive block of ten memory spaces is reserved for the array's contents. So your computer code may be:

1. Make me an array capable of holding ten numbers ..... computer goes away and fences off memory, specifically a ten individual spaces which are one after the other, each one of those ten spaces are capable of holding a single number, just like a single line on your page. All ten together is your array, or the bit of paper you have fenced off.
2. Write the number 34 in array space three..... so computer goes away and in the third block of the memory it reserved, writes the number 34. The same as you writing 34 on the third line of your paper
3. Write the number 10 in array space five.... same thing, goes away and finds the fifth block of memory it reserved, writes the number
4. And so on...

Each one of those blocks of memory has an address. So when it created this array, it generated addresses. (Technically it did not, but for our purposes, we can say that it did). So memory address 1 will be the space for the first number in the array, memory address 2 for the second and so on.

Now back to your ultrasound. Your scanner is going to generate a lot of pieces of data. If you look at an ultrasound picture, mentally divide the whole thing up like a lattice (arbitrary numbers here) so your image has 500 rows and 500 columns. If you look at any one square, it will be a particular intensity of black and white (assuming your ultrasound is B&W). This intensity (brightness, how grey it is) of this specific black and white square is determined by the sound wave returned by your ultrasound scanner. Now this one particular square will need to be stored in the computer memory somewhere and the software running the show will ideally need to know where that one square is. This is where your address generation will come into things. Given the size of the image, it's unlikely the computer could store the whole image in a continuous block of memory, more likely the image is scattered around the memory anywhere.

Now of course, an ultrasound image isn't static, it updates. So if you're scanning a pregnant woman, the foetus will move about, or you may re-position the scanner slightly, what have you. The intensity of the sound wave being returned in each individual square will change X number of times per second. Remember our old TVs would scan down the image 50 times per second? Ultrasound will scan through the image X number of times per second too. So logically, each of those squares will "update" each time that scan happens. The address generation is necessary so the software can take that intensity data and pop it into the correct address.

So to briefly bring that all together, your ultrasound scanner "rasters" over the area to produce an image, that is shoots out soundwaves, reads the intensities and feeds that back to the computer, many times per second given the area it must cover and how many times it needs to update. The computer has to store all these intensities generated from the scanner and needs to remember where they are so the software running the whole show can find these intensities again and create an image for you to see. The computer will throw all this data (remember it's receiving a lot of data very quickly) somewhere in memory and generate addresses for the main software to use later on.

A logic computer is, I would guess, just a fancy way of saying "a computer running special software for ultrasound".

I hope that helps and wasn't too patronizing. Do check with your lecturer though as I am not in any way a qualified ultrasound expert. I'm just relaying what those words mean to me and how they combine in that context.