portable n mobile unit

Portable and mobile

radiographic unit

Presented by :Sudil PaudyalB.Sc .MIT 2nd yr

IOM MMC

PORTABLE N MOBILE EQUIP BY SUDIL 2

Introduction

• Machines used for severely ill and unable patients, who cannot be brought in the radiology department.

• Can be broadly divided into two types: Portable and Mobile equipment.

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Portable unit

• Portable - can be carried by one able bodied person at a time.

• Can be taken around the hospital, some place distant from hospital or even to a patient’s home.

• Simple

• Can be dismantled for transfer.

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Fig: portable radiographic units then (1912) and now


Components

1. Tube head:(A) X-ray tube: Self-rectified, Stationary anode, single focal spot of 1.0mm.

(B) High-tension generator: Tube and generator are enclosed in one oil filled

tank, described as tank construction and the whole enclosure called the tube head.

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2. Tube stand:

• support for the tube head,

3. A small control unit:

• Rheostats: to vary the mA and kV.

• Timer (s).

• Exposure switches.

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Fig: Schematic diagram of components of portable unit

PORTABLE N MOBILE EQUIP BY SUDIL

Advantages • permit radiographic examination in locations limited by the

availability of a standard electrical supply.

Disadvantages• Low output a typical maximum is 80 KVp at 15 mA for 1

second.• Difficult to maintain aspects of radiation protection.

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Mobile

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• Mobile means capable of being moved.

• Mounted on wheels with the motion brake provided.

• Larger and heavier than portable sets and need to be motorized or pushed by human power.

• Motorized units require less effort but add to weight and cost of the unit.


Fig: Mobile units in 1940-1955 and now.


Components

• Tube

• Tube stand

• High tension transformer

• Control unit

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Tube:

• Dual focus rotating anode x ray tube .

• Focal spot About 1.0mm for fine focus 2.0 mm for broad focus.

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Tube stand:

• A strong vertical column mounted on the base that supports the cross arm which carries the x ray tube.

• Range of movements: Can be split into five major components. To prevent damage to cables

movements should have mechanical stops.

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Rotation around the centre of the column, (R)

Cross arm movements the extension of the tube head away from the centre of the column ,(A)

Rotation around the axis of the cross arm, (D)

Angulations across the long axis of the tube head,(B)

Vertical movement up and down main column (H)143/26/2012


High tension generator:

• Gives a max output of 300mA and 125KVp.

• Includes full wave rectification provided by means of selenium rectifiers .

• The H.T. generator, its rectifiers and filament transformer for tube enclosed in one oil filled earthed steel tank.

• Connected to the x ray tube by means of high tension cables.

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Control unit:

• Located behind the generator tank on the base of unit.

• It consists:Mains on/off switchmAs selectorkV selectorFocal spot selectionBody part selectionExposure indicator

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Mobile classificationBy two ways: 1. By power supply:• Capacitor discharge unit• Battery powered unit

2. By output: Low Power Mobiles: 10 to 30mA and 40 to 90 kVp. Average Power Mobiles:100 to 150 mA and 40-95

kVp. High power mobiles : upto 300 mA and 125 kVp.

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Capacitor Discharge Mobile UnitPrinciple:• When charge circuit is activated, voltage from HTT charges

a capacitor up to the kilo voltage required for the exposure.

• The capacitor becomes source of power for x ray exposure. It is disconnected from the charging circuit and connected to the x ray tube for exposure.

• Its discharge through tube constitutes the mAs of the radiographic exposure factors.

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Fig : showing the working of capacitor discharge unit


CONTD…

• When the charge button is pressed ,the capacitor is charged through high tension source by connections at G1andG2.

• when required kV is reached ,charging is automatically stopped and the lamp indicates ready.

• After charging has stopped when exposure button is pressed, capacitor is connected to tube at X1 and X2.it discharges through the tube and constitutes the x ray exposure.

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kV drop:• In a 1μf design the kV drop is around 1 kV per mAS

used and the effective voltage is 1/3 of the voltage drop lower than the starting voltage.

• Hence the equivalent kV=Starting kV-1/3 x mAS • Example for an exposure of 87Kv and 20mAS: • 87-(1/3 x 20)= 87-6.6 = 80Kv Effective.

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X-ray Tube:• Rotating anode tube with single focal spot size of 1.2mm

and heat storage capacity of 80,000 HU.Grid controlled: • Uses a third electrode i.e. focusing cup to control flow of

electrons from filament to target.• Voltage across filament-grid produces electric field along

path of electron beam that pushes e-s closer.• Exposure start & stop controlled by voltage on grid. • Large enough negative voltage on grid blocks tube current

from cathode to anode.

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+


Control Unit• Automatic charging circuit for charging the capacitor.• The kV range is from 30kv to 125kv. If pre selected Kv is

altered after charging, the tube voltage is automatically adjusted to the new value.

• A single mAs control, rather than mA and exposure time being selected separately. The units are usually designed to operate at a high, fixed mA value, so that exposure time becomes the main variable by default.

• mAs control has 15 steps range from 2 mAs to 60 mAs.

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Advantages:• less bulky and easily controllable.

• No need for special installations as power is only required to charge the capacitor.

• The voltage waveform across x ray tube is uniform rather than pulsating. It has no relationship with ac mains.

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• Shorter exposure time by use of grid controller.

Limitations:• Limited mAs output. • The maximum output range is 30-50mAs so cannot

be used for heavy body part such as spine and abdomen.

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Battery Powered Mobile Unit• Also called cord less mobile unit. • Ni-Cd batteries are used as a source of energy for x ray

exposure .• The generator is referred to as constant potential

generator (CPG).• Power supply is used to charge the batteries.• The batteries produces low voltage DC charge.

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Major Components of battery Powered X Ray machine

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Advantages

• Stores considerable energy to generate x rays. can store 10,000 mAs.

• Make exposures independent of power supply.

• Supplies constant output of KV and mA through out the exposure.

• Used in case of emergency power failure.

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Disadvantages

• Batteries must be charged

• Requires regular batteries maintenance

• Heavy

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Care and maintenance:

• The unit should be left connected to the mains power supply of (200v or 115v):

– Every night. – During weekends. – At all times when the unit is idle (not being used).

• Naked flames or lighted cigarettes should not be held near the batteries when they are being charged.

• The acid level in the batteries should be checked every 2 weeks.

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Mobile Image Intensifiers Units

• Used in operating theatre for fluoroscopy examination.

• This reduces the number of radiographs taken and saves the time during surgery.

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Essential features of mobile unit for fluoroscopy

• The x ray tube

• The image intensifier

• High tension generator

• Control consol

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The x ray tube and image intensifier:-

• Mounted opposite to each other at the end of C –arm.

• X ray tube head is at the lower end of C arm and the image intensifier is at the upper end with input phosphor facing towards the x ray tube.

• The tube head houses the x ray tube.• The x ray tube is stationary anode and two focal spots.

• A small focal spot of size 0.6mm is used for fluoroscopy and a large focal spot of size 1.8mm is used for radiography.

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• The C arm is mounted on a cross arm which extend from a carriage carried on a vertical support rising from the control console.

• The x ray tube and the image intensifier are held directly opposite to each other with x ray beam permanently centered to the input phosphor.

• At the back of I.I. is the television pick up tube, so that image can be viewed on monitor.

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• The input phosphor of the image intensifier is cesium iodide which gives good contrast.

• A secondary grid of grid ratio 5:1 is used.

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Movements

• The vertical support can be raised and lowered and the cross arm can be extended through the carriage.

• The x ray tube and image intensifier are attached to the c arm and move together.

• The c arm can be moved in any direction. so the equipment enables a good range of positions and projections to be used without wastage of time.

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High tension generator:

• The x ray tube and high tension generator are together in the tube head.

• High tension generator are single phase with full wave rectification provided by silicon rectifiers i.e. the generator is two pulse.

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Fig: Block diagram of sequence of transference of signal


Control unit : • Kilovoltage for fluoroscopy or radiography range

from 50kv to 105kv.

• mA settings or fluoroscopy range from 0.1to 3.0mA.for radiography the Kv and mA are linked .i.e.

50mA at 55kv 40mA at 80 Kv 30mA at 105 Kv

• The timer for radiographic exposure is electronic and gives range from 0.1 to 3.0 sec.

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• For the television chain, circuit includes controls which allow the image to be transposed right to left and inverted top to bottom.

• There is control for memory circuit with two magnetic disc that is image storage is possible.

• There is facility for pulsed fluoroscopy with electronic selector: the rates provided vary from 1 flash per sec to 1 flash every 5 sec.

• This allows to monitor dynamic events without subjecting the patient to continuous radiation.

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Advancements

High frequency generator mobile units

Computed radiography mobile x ray unit

Direct radiography mobile x ray unit

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High Frequency Generator• Recently high frequency generators are more popular

for use in radiology for mammography and mobile units.

• One of significant advantages is its compact design.

• Converts low frequency (60 HZ) to high frequency (KHZ) pulsed DC, by altering waveform of incoming electrical circuit which is subsequently increased to kilovolts, rectified and sent to the x-ray tube.

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• Produces a nearly constant voltage wave form with extremely low ripple(<1%).

• Provides great x-ray quality(effective energy) and quantity. More efficient.

• More expensive than previous mobile units.

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• Uses inverter circuit. • The DC power supply produces

a constant voltage from either a single phase or three phase input line source.

• inverter circuit creates the high frequency AC waveform.

• This AC current supplies the high voltage transformer and creates a waveform of fixed high voltage and corresponding low current.

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• After rectification and smoothing two high voltage capacitor on the secondary circuits accumulates electron charges. These capacitors produce a voltage across the x-ray tube, that depends upon the accumulated charges

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Fig: Block diagram of high frequency generator


Mobile CR

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Digital portable unit

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Construction

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• Includes a transport case housing several components, a digital x-ray image sensor and x-ray generator.

• Sensor is coupled to a stand that is mounted to transport case.

• Generator is positioned opposite to centre of sensor.• A pt. support unit is disposed b/w image sensor and

x-ray generator.• Image acquisition unit connected to generator and

image sensor and mounted on transport case.• An image display unit is connected to image

acquisition unit and spaced from generator.

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• Tube is positioned above stand to facilitate image generation

• Image acquisition unit includes a display to allow the user to view information relating to control and operation of digital x-ray sensor and tube.

• Display comprises of a touch screen display. An image display unit may also be provided to permit the radiologist to view images at a distance from the tube.

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• The image sensor is a thin film transistor (TFT) based digital x-ray image sensor. Preferably, digital image sensor is about the same size as standard medical x-ray films. The sensors can be grouped into two categories:

• 1)indirect x-ray sensors• 2) direct x-ray sensors

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indirect x-ray sensors: feature a TFT photodiode array that is sensitive to visible light. These sensors are covered by an x-ray to light converter such as gadolinium oxysulfide or cesium iodide which converts each incident x-ray photon into light photons. The light photons are converted into electronic charge at each pixel photodiode.

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direct x-ray sensors: is coated with amorphous selenium which converts incident x-rays directly into electronic charge at each pixel.

• In both cases electronic charge distribution collected by pixel array is proportional to intensity distribution of x-ray photons. This charge distribution is digitized and stored in a computer.

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• In order to display images generated by image sensor image display unit is provided with software that at least supports images in DICOM and JPEG format.

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Table : Tube parameters of digital portable


Digital mobiles

• The digital mobile units are the ultimate solution to mobile X-ray imaging for digitization in ER, traumatology, intensive care units (ICU), in patient wards and pediatrics.

• The system represents an evolutionary move in mobile diagnostic imaging equipment and includes unique features in terms of operability, mobility and image quality.

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• The system meets today’s and future clinical demands providing the premium solution for

immediate image processing

an efficient clinical workflow

a rapid display of high-quality clinical images

fast integration into the hospital network

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Digital mobile units

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Features

• Generator: High frequency generator

• Kvp Range: 40 - 100 Kvp, adjustable in 1 kV increments

• mA range: Fixed, 15 mA and 30 mA

• mAs Range: 0.15 – 120 mAs

• Exposure Time: 0.01 - 4.00 s

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• Indicators: Digital display of kVp, mAs and Time, X-Ray, Ready, mA Station and Fault Indicators

• Exposure Switch: Detachable two position switch

• X-Ray Tube: Stationary Anode Filtration-2.7 mm aluminum

Target Material: Tungsten Anode Capacity: 30,000 HU Storage Focal Spot: 1.0 mm Target Angle: 15 degree.

• Detectors: f p ds amorphous selenium or silicon

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Questions • What are the features of portable unit?• What are the features of mobile unit?• How does a capacitor discharge mobile unit works?• What are the major components of battery powered

mobile unit?• What are the features of mobile image intensifier

unit?• How does a high freqency generator works?• Description of digital portable unit?• What are the features of digital mobile units?3/26/2012


References

• Chesney’s equipment for student radiographers• Christensen’s physics of diagnostic radiology• Cho et.al. Digital mobile radiographic apparatus• Various other websites and ppts.

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Thank you

portable n mobile unit

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