RT II Final April 24, 2009

Good Luck. Follow this link to the Final.

Easter Quiz April 10, 2009

Easter Quiz HERE.

Fluoroscopy

The powerPoint presentation below covers material that was presented in class on April 3, 2009. The quiz scheduled for April 10th will be based on the information in the presentation. View it HERE also.

The X-ray Circuit

The x-ray circuit is composed of two major secondary regions or circuits:
1. the filament circuit (outlined in red on the diagram below), and
2. the high voltage or high tension circuit (outlined in blue)

The filament circuit gets its power supply directly from the autotransformer and supplies current to the filament of the x-ray tube. The major components of the filament circuit are:
1. the mA selector
2. the focal spot selector
3. the step-down transformer

The Filament circuit is switched on when the prepare button is pressed. This sends current through the filament wire causing thermionic emission which produces a space charge. Prepping for too long before each exposure will put undue stress on the filament wire. So keep your prep time optimal (just right--which usually means short).
The mA selector functions as a rheostat (which is a variable resistor--you adjust the resistance to vary the amount of current flowing in the filament circuit). The amount of filament current determines how hot the filament wire gets. (More current--more heat---more electrons boiled off the filament wire--higher mA).

The focal spot selector is a switch that allows current to flow through one filament wire at a time. When you select the large focal spot the filament current flows through the longer filament wire, and when you select small focus the filament current is switched to flow through the small filament wire.

The step-down transformer steps down the voltage in the filament circuit. In the diagram to the left, there are two sets of windings or turns in the step down transformer (in yellow). There are more windings or turns on the upper part of the transformer (the primary side), than on the lower side (the secondary).

The step-down transformer steps down the voltage, but steps up the current. Therefore, in the filament circuit we get low voltage and high current.

Remember, the filament current has to be high to ensure adequate thermionic emission. This is how we control the quantity of electrons boiled off at the filament.

The mA selector and focal spot size selector are located in the primary portion of the step-down transformer. (see diagram above)

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The high voltage portion of the x-ray circuit (shown in blue in diagram 1 above), controls several important aspects of x-ray production. In the high voltage circuit you will find components such as:
1. the pre-reading kV meter--that indicates the kilovoltage that will be applied to the x-ray tube once the x-ray exposure starts (the potential difference between cathode and anode)

2. the exposure switch that closes to start the x-ray exposure and opens to end the exposure. The operator (you) start the exposure, but the amount of time the circuit stays closed is determined by the timer. (So you start it, but you don't end it).

3. the timer controls the amount of time the x-ray exposure lasts.

This is the sequence of events of an x-ray exposure: Once you press the exposure button the high voltage circuit is closed. This means that a high potential difference is set up between the cathode and anode. The electron cloud (space charge) that was produced during the prep phase of the exposure is pulled across form the cathode to the anode based on electrostatic attraction. (negative electrons attracted to positive anode).

The electron flow from cathode to anode is called tube current. As long as tube current is flowing x-rays are being produced.

The tube current will flow as long as the high voltage circuit is closed.

4. the step up transformer--steps up the voltage by a fixed ratio. If the turns ratio (number of secondary windings divided by number of primary windings--Ns/Np) is 1000 the voltage in the secondary portion of the transformer will be 1000 times the primary voltage.

The region highlighted in yellow below is the primary of the step-up transformer.

The region highlighted in blue below is the secondary of the step-up transformer.

5. the rectifiers convert alternating to direct current (pulses) ensuring that tube current only flows in one direction (from cathode to anode)

6. the mA meter--indicates the tube current.

Quiz 2...The Late Edition

Follow this link for the quiz. Submit it by 11:10. If you are late it will not count.

Diagrams for Practice Quiz

Diagram for question 12:






Diagram for questions 14, 15, and 16

Let's Get The Spring '09 Semester Rolling

Welcome back for more hard work ladies and gents. The syllabus is up.

This course covers large portions of sections B and C of the ARRT examination.

What will you have to do to get that A in RTC 105?

1. Develop a web log--7%
2. Do Online Practice Quizzes--8%
3. Demolish 5 In-Class Quizzes--(5 @ 10% each) 50%
4. Complete Laboratory Worksheets and Assignments--10%
5. Beat down a Comprehensive Final Examination--25%

Sounds simple, right? You know I like to make it easy for you.

But it gets easier...you also have to show up for class on time and attend all the class sessions between now and the end of April. Wow!!! You guys are sooo lucky.

Stochastic vs Non-Stochastic Effects

I was asked a question about the difference between stochastic and non-stochastic effects of radiation, and I decided to make my answer public.

Everyone is concerned about how radiation dose affects their body. The way the human body responds to radiation dose (dose-response) is classified into two broad categories of health effects: stochastic and non-stochastic. Non-stochastic is also called deterministic.

Stochastic Effects
Stochastic effects are typically associated with long-term, low-level (chronic) exposure to radiation. The word "Stochastic" refers to the likelihood or probability that an effect will happen. In the diagnostic range of x-radiation that Radiographers and the general public are exposed to, increased levels of exposure make these health effects more likely to occur, but do not influence the type or severity of the effect.

The primary stochastic effects are: Cancer and genetic defects.

Cancer is considered by most people as the primary health effect from radiation exposure.

Radiation can also cause changes in DNA, the "blueprints" that ensure cell repair and replacement. Changes in DNA are called mutations.

Sometimes the body fails to repair these mutations or even creates mutations during repair. The mutations can be teratogenic or genetic. Teratogenic mutations are caused by exposure of the fetus in the uterus and affect only the individual who was exposed. Genetic mutations are passed on to offspring.

In summary, Stochastic effects are:

*totally random (occur by chance)

*appear in non-exposed persons as well as exposed persons

*No Threshold--any dose can cause an effect

*the likelihood of an effect increases as the radiation dose increases, but a single photon can cause an effect

*the severity of the response is independent of the dose (the severity of cancer is not associated with the amount of dose received. You are more likely to get cancer if you receive a higher dose, but the severity of the disease is not based on the dose)

Non-Stochastic (Deterministic) Effects

Non-stochastic effects are those in which the severity of the effect varies with the dose and for which a threshold value exists.

Non-stochastic effects appear in cases of exposure to high levels of radiation, and become more severe as the exposure increases. Short-term, high-level exposure is referred to as 'acute' exposure.

Many non-cancerous health effects of radiation are non-stochastic.

Unlike cancer, health effects from 'acute' exposure to radiation usually appear quickly. Acute health effects include burns and radiation sickness.

Radiation sickness is also called 'radiation poisoning.' It can cause premature aging or even death. If the dose is fatal, death usually occurs within two months. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function.

Summary of non-stochastic effects:

*Threshold--A certain minimum dose must be exceeded before the particular effect is observed. Because of this minimum dose, the non-stochastic effects are also called Threshold Effects. The threshold may differ from individual to individual

*The severity of the effect increases with the size of the dose received by the individual. (More dose more severe effect)*There is a clear relationship between exposure to radiation and the observed effect on the individual.

Examples of Non-Stochastic effects:

RTC 100--Powerpoint Presentation

View Presentation here:

Comparison of Meiosis and Mitosis

Mitosis Animation

RTC 201--The Cell Cycle

View and Chat

RTC 201--The Human Cell

View and Chat

RTC 100--Technique Chart

View Presentation here:

RTC 100--Group 6 Presentation

View the presentation and chat

RTC 100--Group 5 Presentation

Topic for Group 5

What factors are used to determine the quality of a radiographic image? What makes an image good, and conversely, what do people see when they look at an image and determine that it is bad?
Discuss the geometric factors and subject factors that affect image quality. Make sure to include images and diagrams to illustrate your answers and emphasize your key points

RTC 100--Group 2 Presentation

Topic for Group 2

Describe the various components of a typical x-ray tube. Make sure you have a clearly labeled diagram of the x-ray tube. What is the function of each component? What are the differences between a stationary anode tube and a rotating anode tube? Also discuss recent innovations in x-ray tube design. What design features have been introduced, and how do these new design features improve on what existed in the older tubes?

RTC 100--Group 1 Presentation

Group 1 presented information on the X-ray Operator Console.

Take a picture of a typical x-ray operator's console. Discuss each of the dials, switches, displays, and buttons on or connected directly to the operator's console. What is the purpose of each component of the console, and how does it impact the production of x-rays and/or the appearance of the radiographic image?

RTC 100--Group 3 Presentation

The first three group presentations went off successfully on Thursday, November 6th.

All the group members did well, and I am extremely proud of the effort that was made.

Below is group three's presentation. I will be posting each presentation online in the upcoming weeks.

Group 3's topic was:

Take pictures of the equipment in your energized x-ray lab. (Table, bucky tray, vertical cassette holder, grid, generator, high tension cables, tube housing, collimator, etc.) Describe the purpose of each bit of equipment in your x-ray room. Your discussion should answer the questions what does it do, or what is it used for?

Judge for yourself how well they did.

RTC 100--PowerPoint Presentation Topics Groups 7 & 8

The following topics will be presented on Thursday November 20, 2008.

Topic for Group 7

Provide details of the use of intensifying screens in Radiography. Use a diagram to discuss the details of the structure of an intensifying screen. Discuss the various screen-film combinations. Describe the handling and cleaning of intensifying screens. What is the result of poor film/screen contact? (Show an image) How is radiographic technique adjusted for variations in screen speed?


Topic for Group 8

Radiography has gone filmless. No film? Just as photography is now predominantly digital, radiography is heading in that direction as well. Discuss the major forms of digital radiography now in use. How do they compare to traditional (film or analog) radiography? For example, how has the introduction of filmless radiography affected Radiology department expenses, workflow, and number of repeats?

Do not get caught up with details of the technology or how digital radiography works. The intent of your presentation is to introduce the class to the current trend in imaging, and the advantages and disadvantages of going digital. Crucial questions that should be answered are: is it cost effective? Does it save on patient radiation dose? Does it expand the availability of images? Are there any adjustments that have to be made by the radiographer to their technique and the way imaging devices are handled? What about workflow? Are there any improvements in patient throughput when we go from film to filmless?