The document discusses the history and components of X-ray machines. It begins with a brief history of the discovery of X-rays by Wilhelm Roentgen in 1895 and important developments in dental radiology. It then describes the ideal requirements and main components of an X-ray tubehead, including the X-ray tube, position indicating device, and collimator. The document explains the circuitry and components within the X-ray tube, such as the cathode, anode, and line focus principle. It concludes with a discussion of advances in X-ray machines.
An X-ray film automatic processor is a device designed to move medical X-ray films from one solution to the next, in the film development process, without the need for human intervention except to insert a film or cassette
An X-ray film automatic processor is a device designed to move medical X-ray films from one solution to the next, in the film development process, without the need for human intervention except to insert a film or cassette
Production of x rays
Components of X-ray
Cathode
kVp , mA , mAs .
Line focus principle
Heel effect
anode
Stationary anode x ray tube
Rotating anode x-ray tube
Grid controlled x-ray tube
Saturation voltage
Metal ceramic x – ray tube
Processes of x- ray generation
intensity of the x-ray beams
Effect of kVp on x- ray beam
Effect of tube current on x- ray beam
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if you notice any mistake comment please ......
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
- Video recording of this lecture in English language: https://youtu.be/lK81BzxMqdo
- Video recording of this lecture in Arabic language: https://youtu.be/Ve4P0COk9OI
- Link to download the book free: https://nephrotube.blogspot.com/p/nephrotube-nephrology-books.html
- Link to NephroTube website: www.NephroTube.com
- Link to NephroTube social media accounts: https://nephrotube.blogspot.com/p/join-nephrotube-on-social-media.html
Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
Pulmonary Thromboembolism - etilogy, types, medical- Surgical and nursing man...VarunMahajani
Disruption of blood supply to lung alveoli due to blockage of one or more pulmonary blood vessels is called as Pulmonary thromboembolism. In this presentation we will discuss its causes, types and its management in depth.
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
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Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
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2 Case Reports of Gastric Ultrasound
Anti ulcer drugs and their Advance pharmacology ||
Anti-ulcer drugs are medications used to prevent and treat ulcers in the stomach and upper part of the small intestine (duodenal ulcers). These ulcers are often caused by an imbalance between stomach acid and the mucosal lining, which protects the stomach lining.
||Scope: Overview of various classes of anti-ulcer drugs, their mechanisms of action, indications, side effects, and clinical considerations.
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
1. Spontaneous remission of a
squamous cell carcinoma of the
floor
of the mouth
C A S E R E P O R T
Good morning
2. P R E S E N T E D B Y
SUCHITHRA K.S
1 S T M D S
D E P T . O F O R A L M E D I C I N E A N D
R A D I O L O G Y
X-RAY MACHINE
3. CONTENTS
Introduction
History
X ray machine
Ideal requirements
Classification
Tubehead
Circuitry
Recent advances
Conclusion
References
4. Introduction
X- rays belong to a group of radiations called electromagnetic
radiation.
X rays are produced by energy conversion when a fast moving
stream of electrons is suddenly decelerated in the “target” anode
of an x ray tube.
The x ray tube is made of Pyrex glass that encloses a vacuum
containing two electrodes. Electrons are produced by the heated
tungsten filament(cathode) and accelerated by a high potential
difference to hit the target anode, where x rays are produced.
5. DISCOVERY OF X RAYS
Wilhelm Conrad Roentgen, a German
Physicist, discovered X-rays on
November 8, 1895
He termed these rays as ‘X Rays’ after the
mathematical symbol for the unknown
– ‘X’ which were ultimately, called
‘Roentgen Rays’.
1st radiograph the human body-
Bertha Roentgen’s hand(exposure time15 min)
6. HISTORY OF DENTAL RADIOLOGY
YEAR DISCOVERY PERSON
1895 Discovery of X rays W.C. Roentgen
1896 First Dental
Radiograph
O. Walkhoff
1896 First Dental
Radiograph in
US(skull)
W.J. Morton
1896 First Dental
Radiograph in US(live)
C.E. Kells
1901 First paper on dangers
of radiation
W.H. Rollins
1904 Introduction of
Bisecting Technique
W.A. Price
1913 First dental text H.R. Raper
7. HISTORY OF DENTAL RADIOLOGY
YEAR DISCOVERY PERSON
1913 First pre-wrapped
dental films
Eastman Kodak
Company
1913 First X ray tube W.D. Coolidge
1920 Concept of paralleling
Technique
F. MacCormack
1920 First machine made film
packets
Eastman Kodak
Company
1923 First dental X ray
machine
Victor X ray
Corporation of Chicago
1925 Introduction of
Bitewing technique
H.R.Raper
8. HISTORY OF DENTAL RADIOLOGY
YEAR DISCOVERY PERSON
1933 Concept of Rotational
panoramic proposed
Dr. Hisatugu Numata
1947 Introduction of Long
cone paralleling
technique
F.G. Fitzgerald
1948 Introduction of
Panoramic Radiography
Dr. Yrjo Veli Paatero
1955 Introduction of D speed
film
1957 First variable
kilovoltage Dental Xray
machine
General Electric
1960 First Panoramic Xray
machine Marketed
S.S White & Co
9. HISTORY OF DENTAL RADIOLOGY
YEAR DISCOVERY PERSON
1978 Introduction of dental
Xeroradiography
1981 Introduction of E speed
film
1987 Introduction of
Intraoral digital
Radiography
1987 Denta scan designed
1998 CBCT European market
2000 Introduction of ‘F’
speed films
2001 CBCT US Market
10. Ideal requirements
The equipment should be:
Safe and accurate
Capable of generating X-rays in the desired energy range and with
adequate mechanisms for heat removal
Small
Easy to maneuver and position
Stable, balanced and steady once the tube head has been positioned
Easily folded and stored
Simple to operate
Robust.
11. TUBE HEAD
It is a tightly sealed, heavy metal housing that contains the
X ray tube that produces dental X rays.
12. Components of tube head
• protect the X ray tube and grounds
the high voltage component
Metal
housing
• filament, copper block and the
target
X ray tube
• step-up the mains voltage of 240
volts to the high voltage (kV)
required across the X-ray tube
Step-up
transformer
• step down the mains voltage of 240
volts to the low voltage current
required to heat the filament
Step-down
transformer
13. Components of tube head
• minimize leakageLead shield
• heat removal, insulation.
(metal bellows)Surrounding oil
• remove harmful low energy
(soft) X-rays
Aluminium
filtration
• shape and limit the beam sizeCollimator
• indicating the direction of the beam and setting the ideal
distance from the focal spot on the target to the skin
Spacer cone or
PID
14. Position indicating devices
The spacer cone or beam-indicating device (BID) or Position
indicating device is a device for indicating the direction of the
beam and setting the ideal distance from the focal spot on the
target to the skin.
The ideal focus to skin (fsd) distances:
— 200 mm for sets operating above 60 kV
— 100 mm for sets operating below 60 kV
The long PID is preferred because less
divergence of X ray beam occurs.
The rectangular type is most effective in
reducing patient exposure.
1.Conical
2. Rectangular
3. Round
1. Short (8 inches)
2. Long (16 inches)
15. X ray tube
All dental and medical x-ray tubes are called Coolidge tubes
because they follow the original design of W. C. Coolidge
introduced in 1913.
The X ray tube in dentistry measures approximately several
inches long by one inch in diameter.(12-18 cm in length and 9 cm
in breadth, made of pyrex glass/borosilicate glass to withstand
high temperatures)
Crookes tube first
16. Components of x ray tube
LEADED GLASS HOUSING
It prevents X ray from escaping in all directions(radiation
leakage)
It has a ‘window’ that permits the X ray beam to exit the tube
and directs the X ray beam towards the Aluminium disc, lead
collimator and PID
Used for earthing.
17. The effectiveness of the tube housing in limiting leakage radiation
must meet the specifications listed in the National Council on
Radiation Protection and Measurements Reports No.49,which states
that,
“The leakage radiation measured at a distance of 1 meter from the
source shall not exceed 100mR in an hour when the tube is operated
at its max continuous rated current for the maximum rated tube
potential.”
18. Usually x ray tube has a glass envelope(pyrex glass) that encloses
vacuum containing two electrodes.
Sun-burning or Sun- tanning of tube – Vaporization of the filament
occurs over a period of time. When the particle vaporize (turn into
gaseous form), they solidify on the glass of the X ray tube, which is
called ‘sun-burning or sun-tanning of the tube.
This reduce the output of the X ray tube, destruction of the vacuum and
integrity of the tube, resulting in ‘arcing’ and ultimate tube failure.
19. metal or ceramic x-ray tubes
This leads to the development of a high performance x ray tube by
Philips Medical Systems under the trade name of “ceramic super
rolatix” tube.
Metal or ceramic tube has a metal casing instead of the usual glass
envelope, and has three ceramic insulators.
Ceramic insulators are used to insulate the high voltage parts of the
x ray tube from the metal tube envelope. Aluminium oxide is a
commonly used ceramic insulator.
Advantages
1. Less off-focus radiation
2. Longer tube life with high tube currents.
3. Higher tube loading.
21. Why vacuum inside???
The x-ray tube is evacuated to prevent collision of the fast-moving
electrons with gas molecules, which would significantly reduce their
speed.
The vacuum also prevents oxidation , “burnout” of the filament.
Also, the electrons that were being accelerated towards the anode
would collide with the gas molecules and cause the secondary electrons
to be ejected ,resulting in a wide variation in the tube current.
The purpose of vacuum in the modern x ray tube is to allow the number
and speed of the accelerated electrons to be controlled independently.
22. Connecting wires must be sealed into the glass wall of the x ray
tube.
During operation, both the glass and the connecting wires are
heated to high temperatures. Because of differences in coefficient
of expansion, most metals expand more than glass when heated
resulting in glass-metal seal to break & would destroy the
vacuum in the tube.
So, special alloys having approximately the same coefficients of
linear expansion as pyrex glass, are generally used in x ray tubes.
23. cathode
Two components:
a) Filament
b) Focusing cup
Filament – source of electron.
It is a coil of tungsten wire about 2 mm in diameter and 1 cm or less in
length
The filament is heated to incandescence by the flow of current from the
low-voltage source and emits electrons
Focusing Cup - the filament lies in a focusing cup, a negatively charged
concave reflector made of molybdenum
The parabolic shape of the focusing cup focuses the electrons into a
narrow beam directed at a small rectangular area on the anode ,the
focal spot
FOCUSING
CUP
FOCAL
SPOT
24. Focusing cup
Modern x ray tubes may be
supplied with a single or more
commonly, a double filament.
Only one filament is used for any
given exposure.
Two additional filament
arrangements such as triple focus
and stereoscopic angiographic tube
is also available.
25. Thermionic emission
The filament is heated to incandescence through a range of
temperatures by varying voltage (10V), across the filament from a step
down transformer in a low voltage circuit.
The hot filament emits electrons that are separated from the outer orbits
of tungsten atoms at a rate proportional to its temperature by a process
called ‘thermionic emission’.
26. • Edison effect
The electron cloud surrounding the filament produced by the
thermionic emission.
• Electrons emitted from the tungsten filament form a small cloud in the
immediate vicinity of the filament. This collection of negatively
charged electrons forms what is called the space charge.
• The tendency of the space charge to limit the emission of more
electrons from the filament is called the space charge effect. The
number of electrons in the space charge remains constant.
27. Anode
The anode consists of a tungsten target embedded in a copper stem.
The purpose of the target in an x-ray tube is to convert the kinetic
energy of the colliding electrons into x-ray photons
This is an inefficient process with more than 99% of the electron
kinetic energy converted to heat
Two types of Anodes:
1. Stationary or fixed anodes
2. Rotating anodes
28. Stationary anode
2 or 3 mm thick tungsten plate embedded in a large mass of
copper.
Tungsten plate is square or rectangular in shape, with each
dimension usually being greater than 1 cm.
The anode angle is usually 15 to 20 degree.
29. Why tungsten ?
High atomic number (74) -A target made of a high atomic number
material is most efficient in producing x rays
High melting point(3380 C) - heat is generated at the anode
High thermal conductivity - readily dissipating its heat into the copper
stem
Low vapor pressure - maintain the vacuum in the tube at high operating
temperatures
30. Why Copper is used ?
Thermal conductor - removes heat from the tungsten, thus
reducing the risk of the target melting
31. Rotating anode
Used to produce x ray tubes capable of withstanding the heat generated
by large exposures
The electrons strike successive areas of the target, widening the focal
spot by an amount corresponding to the circumference of the beveled
disk, thus distributing the heat over this extended area
The focal spot of a stationary tube is now a focal track in rotating anode
machines
Used in tomographic ,cephalometric
units ,medical computed tomography
x-ray machines
32. Structure
The anode of rotating anode tube consists of a large beveled disc of
tungsten, or an alloy(90%tungsten and 10%rhenium) of tungsten
disk (The angle of bevel vary from 6 to 20 degree, to take advantage of
the line-focus principle), which theoretically rotates at a speed about
3600 rpm when exposure is being made
The magnetic field produced by the
Stator coils induces a current in the
copper rotor of the induction motor,
and this induced current provides the
power to rotate the anode assembly.
33. Electron beam striking an area
(assume a 7mm high&2mm wide area)
Stationary anode - 7×2 = 14 sqmm
Rotational anode – track of 7mm wide that extends
around the periphery
The typical disc diameter measure 75, 100 or 125 mm.
34. Factors to be considered
Heat dissipation - the stem is made up of Molybdenum (high melting point
(2600c) & poor heat conductivity)
Length of Molybdenum Stem – inertia – bearings at each end of the anode axle
Lubricant - vaporize and destroy the vacuum - the use of metallic lubricants
(especially silver)
Roughening of the focal track - very rapid heating and cooling of the surface -
an alloy of about 90% tungsten and 10% rhenium
Speed of rotation –
1. Length of the anode stem is made as short as possible to decrease the
inertia of anode
2. The anode assembly rotates on two sets of bearings, which are placed as
far as possible
3. The inertia is reduced by decreasing the weight of the anode by a
compound anode disc in which the largest part of the disc is made of molybdenum
(specific gravity 10.2), which is lighter than tungsten( 19.3).
35. Methods of heat dissipation
1. Conduction : through the Copper stem
2. Convection : through the oil surrounding the tube
3. Radiation : through the radiator device attached to the copper
stem
4. Rotating Anode
36. Focal spot and line focus principle
The focal spot is the area on the target to which the focusing cup directs
the electrons and from where x rays are produced.
Most of the energy of the electrons is converted in to heat, with less
than 1% being converted into x rays.
The sharpness of image increases as the size of the focal spot
decreases, but heat/area increases.
This conflicting need of a large focal spot to allow great heat loading
and a small focal area to produce good radiographic detail, were
resolved in 1918 with the development of line focus principle.
37. The target is inclined about 20
degrees (ANGLE OF
TRUNCATION) to the central
ray of the x-ray beam. This
causes the effective focal spot
to be approximately 1 × 1 mm,
as opposed to the actual focal
spot (1 × 3 mm)
38. The anode angle differs
according to individual tube
design and may vary from 6 to
20 degree.
For general diagnostic
radiography done at 40-in focus
film distance, the anode angle
is usually no smaller than 15
degree.
Focal spot size is expressed in
terms of the apparent or
projected focal spot, sizes of
.3,.6.1.0,1.2mm are commonly
employed.
39. Heel effect
The intensity of the x ray beam that leaves the x ray tube depends on the angle at
which the x rays are emitted from the focal spot. This variation is termed as the
‘heel effect’.
The decreased intensity at the anode side is caused by the absorption of the x ray
photons by the target itself
Significance :
1. The intensity of film exposure on the anode side
of the x ray tube is significantly less (thicker parts of
the body should be placed towards the cathode side)
2. The heel effect is less noticeable when larger
focus-film distances are used.
3. For equal target film distances, the heel
effect will be less for smaller films. (the intensity
of the x ray beam nearest the central ray is more uniform)
42. X-ray generators
An x ray generator is the device that supplies electric power to the x-
ray tube.
The tube requires electrical energy for two purposes.
1. To boil electrons from the filament-filament circuit.
2. To accelerate these electrons from the cathode to the anode-
high voltage circuit.
• The generator has a timer mechanism ,a third circuit, which regulates
the length of exposure and a group of rectifiers for the high voltage
circuit.
43. There are two basic circuits in a diagnostic x ray unit.
One circuit contains the step up transformer and supplies the high
voltage to the x ray tube.
The other circuit contains a step down transformer and supplies the
power that heats the filament of the x ray tube.
A transformer called the “autotransformer” supplies the primary
voltage for both these circuits.
46. Filament circuit
Regulates current flow through the filament of the x ray tube.
A current flow of 3 to 5 A with an applied voltage of about 10V are
typical values.
The power to heat the x ray tube filament is provided by a small step
down transformer called the “filament transformer.”
Precise control of filament heating is critical, because a small variation
in filament current results in a large variation in x-ray tube current.
In addition, stabilizing and compensating circuits are also present.
47. High voltage circuit
The circuit has two transformers, an autotransformer and a step up
transformer.
The autotransformer is actually the kVp selector and is located in the
control panel.
48. The step up transformer increases the voltage by a factor of 600 and the
potential difference across the secondary coil may be as high as 150000
V.
Two meters are present in high voltage circuit,one to measure
KVp(“prereading peak kilovoltmeter”) and the other to measure mA.
KVp-indicate the potential across the x ray tube
mA-indicate the actual current flowing through the tube during an x ray
exposure.
KVp meter is placed in the circuit between autotransformer and step up
transformer and mA, at the center of secondary coil where the
transformer is grounded. Both the meters can be located on the control
panel with a minimum of insulation and without serious risk of electric
shock.
49. Tube current
The tube current is the flow of electrons through the
tube; that is, from the cathode filament, across the
tube to the anode, and then back to the filament
Transformer
reduce voltage
to10 V
mA selector
adjust I to 10
mA
Regulates
filament
temperature
Regulates no of
electrons
50. Tube voltage
kVp selector
adjust primary
voltage
Secondary voltage
applied to step-up
transformers
110V becomes
60,000 to
100,000V
Increase energy of
electrons
Sufficient energy
for X ray
production
A high voltage is required between
the anode and cathode to give
electrons sufficient energy to
generate x rays
51. Rectification
Process of changing alternating current into direct current and the
device that produces the change is called a rectifier.
The high voltage transformer provides an alternating voltage for the x
ray tube.
52. Half-wave rectification
Current flows only when anode is + ve & cathode – ve
The half of the cycle where cathode is + ve & anode – ve ,where there
is no flow of electron is Inverse Voltage or Reverse bias.
The circuitry in which the alternating high voltage is applied directly
across the x-ray tube, limits x-ray production to half the AC cycle and
is called self-rectified or half-wave rectified.
Self rectification has two disadvantages-
Prolonged exposure times.
Destroy the filament
53. Therefore, to protect the x ray tube and to improve the efficiency of the
x ray production, special rectifiers are incorporated into the high
voltage circuit.
54. Full wave rectification
In Full-wave rectified , constant potential between anode
& cathode.
Mean energy of X ray beam is higher
Longer contrast scale
Patient receives less dose
55. The principal disadvantage of pulsed radiation is that a considerable
portion of the exposure time is lost while the voltage is in valley
between two pulses. the time spent bombarding the target with low
energy electrons does little except to produce heat in the target and to
produce low energy x rays, which are absorbed in patient and raise
patient dose.
This lead to the development of three phase generators, capacitor-
discharge generators, battery powered generators, medium frequency
and falling load generators…
57. Exposure timers
A variety of ways to control the length of an x ray exposure
have been developed.
There are four basic types of exposure timers-
Mechanical timers
(rarely used today)
Electronic timers
Automatic exposure control
(phototimers)
o Pulse – counting timers
58. Electronic timers
The electronic timer controls the length of time that high voltage is
applied to the tube and therefore the time during which tube current
flows and x rays are produced.
The length of the x ray exposure is determined by the time required to
charge a capacitor through a selected resistance. The exposure button
starts the exposure and also starts charging the capacitor and is
terminated when the capacitor is charged to a value necessary to turn
on associated electronic circuits.
59. Subjecting the filament to continuous heating at normal operating current
shortens its life.
To minimize filament damage, the timing circuit first sends a current
through the filament for about half a second to bring it to the proper
operating temperature and then applies power to the high-voltage
circuit.
60. Phototimers
Mechanical and electronic timers are subject to human error.
Phototimers measure the amount of radiation required to produce the
correct exposure for a radiographic examination.
The essential element in phototimers is a device that can detect
radiation and in response to this radiation, produce a small electric
current. There are three such devices-
Photomultiplier detectors
Ionization chambers
Solid state detectors
Phototimers can be located in front of the cassette, and are called
entrance types, or behind the cassette as exit types.
61.
62. Tube Rating
The total load that can be safely accepted by an x ray tube is a function
of the heat energy produced during the exposure.
The rate at which heat is generated by an electric current is proportional
to the product of the voltage (kV) and the current (mA).
Thus the total heat produced is a product of voltage and current and
exposure time. This energy is currently expressed in two different
systems.
Heat units(an artificial system)(mA*kVp*sec)
SI units(the watt-second or joule)
63. The heat storage capacity for anodes of dental diagnostic tubes is
approximately 20KHU.
Another parameter that measure x ray tube loading is kilowatt
rating. It is commonly used to express the ability of the tube to
make a single exposure of a reasonable duration(for 0.1 sec) and
always calculated for an x ray tube with a constant potential and
high- speed rotation.
64. Tube Rating Charts
An x ray tube rating chart help us to calculate the approximate kW
rating.
kW rating of a tube
that accept an exposure
of 70 kVp and 500 mA
at 0.1 sec is-
70kVp*500mA=35000w
=35kW
So this a 35-kW tube.
65. Each x-ray machine comes with a tube rating chart that describe the
longest exposure time the tube can be energized for a range of voltages
(kVp) and tube current (mA) values without risk of damage to the
target from overheating.
Anode heat-storage chart is used to determine the length of time the
tube must be allowed to cool before additional exposures can be made.
Duty cycle relates to the frequency with which successive exposures
can be made. It must be long enough for heat dissipation and this
characteristic is a function of the size of the anode and the method used
to cool it.
66. Summary
X rays are produced by energy conversion when a fast moving
stream of electrons is suddenly decelerated in the target of an x
ray tube. An x ray tube is a specially designed vacuum diode
tube. The target of an x ray tube is usually tungsten or an alloy
of tungsten. Heat production in the x ray tube is minimized by
using the line focus principle and a rotating anode.
67. An x ray generator supplies electrical energy to the x ray
tube and regulates the length of the radiographic exposure.
Single phase generators have half wave rectification. Three
phase generators may be six pulse or twelve pulse.
Transformers are given a rating that indicates the
maximum safe output of the secondary windings. Such ratings
are expressed as the kilowatt rating.
68. references
Oral radiology – Principles and Interpretation - 6th Edition
Stuart C White & Michael J Pharoah
Christensen's Physics of Diagnostic Radiology – 4th Edition
Oral radiology – Principles and Interpretation - 5th Edition
Stuart C White & Michael J Pharoah
Essentials of dental radiography and Radiology- 3rd
Edition,
Eric Whaites
Fundamental physics of radiology –W.J. Meredith – 3rd
Edition
Essentials of Oral & Maxillofacial Radiology – Freny R
Karjodkar
Editor's Notes
With rise in temperature, the oil expands and occupies greater volume. It is essential that there should be no air bubbles within the space surrounding the glass. This is solved by inserting ‘metal bellows’, which extends as the heated oil expands, simultaneous acting as a safety device. If bellows expand beyond a certain point then they operate a micro switch which prevents operation of the tube until the oil has cooled sufficiently.
The parabolic shape of the focusing cup focuses the electrons emitted by the filament into a narrow beam directed at a small rectangular area on the anode called the focal spot.tungsten filament is coiled to form a vertical spiral about 0.2 cm in diameter.
The target and rotor (armature) of the motor lie within the x-ray tube, and the stator coils (which drive the rotor at about 3000 revolutions per minute) lie outside the tube
. In the rotating anode tube, absorption of the heat by the anode is undesirable because heat absorbed by the bearing of the anode assembly would cause them to expand and bind
, the stem , which connects the tungsten target to the reminder of the anode is made up of Molebdenum. Molebdenum has a high melting point (2600c) and is a poor heat conductor
Almost all conventional dental x-ray machines are self-rectifi ed.