Introduction to BME LAB

Lec.5:Introduction to the x-ray system

Dr. Qabas Khalid

Contents

1 Introduction

2 Properties of X-rays:

3 Biological Effects of Using X-ray on Biological Cells:

3.1 Direct Damage: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.2 Indirect action or damage: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Inside the Operation Room:

4.1 X-ray Tube: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.1 Housing case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.2 The anode: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4.1.3 The cathode: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 References

Introduction

X-ray: is an invisible, highly penetrating electromagnetic wave of much shorterwavelength (higher frequency) than visible light. The wavelength range for x-rays is fromabout 10−8m to about 10−12m as shown in Figure (1), the corresponding frequencyrange is from about 3*1016 Hz to about 3*1020Hz.

It has many applications in different fields of life. X-ray is used in very wide range ofapplications including medicine, engineering, security all these applications depends onpenetrating ability of X-ray. However, one of its major disadvantages is the health riskassociated with the radiation.

In medical fields, it consider as an efficient non-invasive, safe (when used in theacceptable doses), and painless tool to image the inside of the human body specially theskeletal bones, as in normal X-ray testing device Figure(2), Computed Tomographydevices (CT scans) as in Figure (3), and in Catheteraization processes Figure (4).

Properties of X-rays:

The energy range of normal X-ray is between100 eV to 10 MeV. Generally, X-rays have theseproperties:

• X-rays are invisible, it is not in the visible range of EM.

• X-rays are electrically neutral. They have neither apositive nor a negative charge. They cannot be acceleratedor made to change direction by a magnet or electrical field.This feature is good in that no electrical device or 50 Hzelectrical line can effect the direction of radiation of X-ray.

• X-rays travel at the speed of light in a vacuum, andapproximately the same velocity in air.

• X-rays cannot be optically focused, since it penetratesphysical objects.

• The x-ray beam used in diagnostic radiography comprisesmany photons that have many different energies.

• X-rays travel in straight lines.

• X-rays can cause some substances to fluoresce.

• X-rays can be absorbed or scattered by tissues in the human body.

• X-rays can produce secondary radiation.

• X-rays can cause chemical and biologic damage to living tissue, that is why it is dangerous to take X-ray test more that one time in six months.

Biological Effectsof Using X-ray onBiological Cells:

Radiation can cause damages toliving tissues in two ways, Figure(5): 1. Direct Damage: as a result ofionization of tissues cells.

2. Indirect damage: as a result ofthe free radicals produced by theionization of water.

3.1 Direct Damage:

When an X-ray photon or any other high energetic ray hits thebiological cells, it will rupture the DNA, RNA and some of theenzymes inside this cell, as shown in Figure (6). This will leadthe cell to do a wrong chemical reactions when during celldivision and may lead to the following symptoms.

• Inability to pass on genetic information to the new cells.

• Abnormal replication, which can cause cancer if not stopped.

• Cell death.

• Only temporary damage – the DNA being repaired successfully beforefurther cell division. This is the case if we follow the safety instructionduring the x-ray test.

If the radiation directly affects somatic cells of the tissue, the effects on the DNA (and hence the chromosomes) could result in a radiation-induced malignancy or cancer as in Figure (7).

If the damage is to reproductive stem cells, the result could be a radiation-induced congenital abnormality.

What actually happens in the cell depends on several factors, including: 1. The intensity and type of radiation.

2. The time between exposures.

3. The ability of the cell to repair the damage.

4. The stage of the cell’s reproductive cycle when irradiated.

3.2 Indirect action or damage:

This process, which is shown in Figure (5),involves the ionization of the water moleculeproducing both ions and free radicals which cancombine to damage the vital biologicmacromolecules such as DNA.

4 Inside the Operation Room:

Operation room , Figure(8), is where the test isdone. So, the main partsof the x-ray machinelocated here, yet in thislecture we will speakabout the x-ray tube only.

4.1 X-ray Tube:

4.1.2 The anode:

Is the positive side of the tube, X-ray tubes areclassified by the type of anode:

1. Stationary, which are used in dental x-ray andsome portable x-ray machine where high tubecurrent and power are not required.

2. Rotating. The rotating anode allows the electronbeam to interact with a much larger target area.The heat is not confined to a small area. Therotation happens by the use of a special motorinside the x-ray tube, as in Figure (11).

exposure, there is a need to cool it, normally this job is done in many ways, Radiation, Conduction, and Convection. Target material: The anode material needs to have:

• High atomic number, increase the production of x-ray as shown in Eq (1).

• Thermal conductivity conductivity, huge amount of heat produced during the x-ray production.

• High melting point.

4.1.3 The cathode:

Is the negative side of the tube and contains two primary parts:

• The filaments.

• The focusing cup.

The filaments is made of Tungsten because of it’s high melting point of 3410𝐶°. X-rays are produced by thermionic emission when a 4A or higher current is applied. Most tube have two filaments which provide a choice of quick exposures or high resolution. The focusing cup has a negative charge so that it can condense the electron beam to a small area of the anode.

References

• For additional reading see:

• http://www.infoplease.com/encyclopedia/science/x-ray.html.

• http://www.nhs.uk/conditions/X-ray/Pages/Introduction.aspx.

• http://www.wikiradiography.com/page/Characteristics+and+Production+of+X-rays.

• http://web.stanford.edu/group/glam/xlab/MatSci162_172/LectureNotes/01_Properties% 20&%20Safety.pdf.

• http://ocw.mit.edu/courses/materials-science-and-engineering/3-091sc-introduction-to-solid-state-chemistry-fall-2010/ syllabus/MIT3_091SCF09_aln05.pdf.

• Fundamental Properties of X-rays .pdf

• http://ocw.mit.edu/courses/materials-science-and-engineering/3-091sc-introduction-to-solid-state-chemistry-fall-2010/syllabus/MIT3_091SCF09_aln05.pdf

• http://www.vetmansoura.com/Radiology/X-RayMachine/Machine1.html

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