Computed TomographyHistory and Technology

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Talking About Innovations

In the 1970s, Computed Tomography (CT) has sparked a revolution inboth medical engineering and medical applications. Today, CT representsnot only a well-established technology in the world of medicine, but haseven advanced to be an indispensable and integral component of routinework in clinics and medical practices.

From the beginning, Siemens Medical Solutions has been an innovationleader in CT technology. Focal points regarding technologicaland design developments have always been patient and user-friendliness, optimized workflow, excellent image quality,and advanced diagnostic possibilities. The goal has beento make CT examinations as comfortable and pleasant aspossible for both the patient and the operator.

This brochure gives a short overview of and insight into thehistory of CT and the technology behind it – from the beginningto the present.

And Siemens will continue to further develop and drive innovationsin CT.

Historical Outline

What is CT?

Components of a CT System

Clinical Use of CT

Milestones in CT1974 – First CT System1987 – First Spiral CT1998 – First Multislice CT2005 – First Dual Source CT

Portfolio of Siemens CT Solutions

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12162026

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1972

Computed Tomography

In London, Godfrey N.Hounsfield’s developmentof computed tomographymarks the beginning ofa new era in diagnosticimaging

11/08/1895

The physicist and laterNobel Prize winnerWilhelm Conrad Roentgen(1845–1923) discoversX-ray radiation

X-ray Radiation

X-ray image ofhis wife’s hand

1974

Instant image reconstruction

First CT System –SIRETOM

SIRETOM CT system

1987/88

Continuous rotationof tube and detector

Shorter examinationtimes

Increased patientcomfort

First Spiral CT –SOMATOM Plus

SOMATOM Plus CT system

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Subsecond spiral CT

Larger volumesacquired faster, shorterbreath hold, improvedthin-slice resolution

Subsecond spiral CT, long MPR,abdomen/pelvis, SOMATOM Plus 4

UFC (Ultra FastCeramic) Detector

Same image qualitywith significantlyreduced radiationdose

1998

Multislice spiralscanning with 4 slicesper rotation

Fastest rotation timeof 0.5 s

First use of Cardio CTin routine operation

First Multislice CT –SOMATOM Volume Zoom

Introduction ofSiemens’ proprietarySTRATON® X-ray tubetechnology

Extremely high coolingrate and smaller tubesize due to direct oilcooling of the anode

2005

Revolutionarytechnologicaldevelopment:Dual Source CTwith two X-ray unitsand two detectorsin one gantry

First Dual Source CT –SOMATOM Definition

1994

SOMATOM Plus 4

1996/97

Lightning UFC™

2003

STRATON®

What is CT?

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Since Wilhelm Conrad Roentgen discovered X-raysin 1895, researchers have been trying to find waysto image the body down to the smallest anatomicaldetail in two and even three dimensions. In the1970s, the British engineer Godfrey N. Hounsfieldand the American physician A. M. Cormack inventedComputed Tomography (CT) by combining X-raytechnology with computers. This special X-raymethod takes slice images from different bodyregions and visualizes not only bones, but also softtissue. For this invention, the two scientists wereawarded the Nobel Prize in medicine in 1979.

CT is considered to be the greatest innovation in thefield of radiology since the discovery of X-rays, asthis imaging technique provides physicians with aninsight into the body that was not possible before.Today, CT is one of the most important methods ofradiological diagnosis. It delivers non-superimposed,cross-sectional images of the body and showssmaller contrast differences than conventionalX-ray images. This allows better visualization ofspecific, differently structured soft-tissue regions,which cannot be visualized by mere X-ray exams.

Wilhelm Conrad Roentgen(1845–1923), thediscoverer of X-rays

X-ray imageof the hand ofMs. Roentgen

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Setup of a CT System

A CT system comprises several components. Thesebasically include:

• The scanning unit, i.e. the gantry, which consistsof the X-ray unit and the detector unit.

• The patient table.

• The image processor for image reconstruction.

• The console.

In CT scanners both the X-ray unit (or tube), whichfunctions as a transmitter, and the detector unit,which operates as a receiver, are housed in a ring-shaped unit called the gantry. In the gantry, thedetector is positioned opposite the X-ray unit. Thepatient table is located in the middle of the gantry.During a CT examination, the gantry rotates aroundthe patient’s body. X-rays passing the body of thepatient are attenuated depending on the thicknessof the tissue. The detector receives these attenuatedX-rays and converts them into visible light.Photodiodes transform this light into electrical signals,which are then converted into digital signals byintegrated detector electronics. These digital signalsare then transmitted over high-speed fiber opticsto the image processor. High-resolution images arethen generated in real-time by complex computercalculations.

The console represents the man-machine interfaceand is designed to be multi-functional. It is the controlunit for all examination procedures and is also usedto evaluate the examination results. To enhanceworkflow, Siemens has developed a double consolecapable of performing both functions at the sametime.

Scanningunit

Patienttable

Imageprocessor

Console

Components of a CT System

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X-ray components

• X-ray unit or tubeManufacturers of CT systems use X-ray units withvariable focal spot sizes. It’s like in photography: forlow-contrast images one needs a large focal spot,whereas high-resolution images with thin slicesrequire a small focal spot. Regarding power, tubesused in modern CT scanners have a power ratingof 20 to 80 kW at voltages of 80 to 140 kV. Thescanner can, however, be operated at maximumpower for a limited time only. These limits aredefined by the properties of the anode and thegenerator. To prevent overloading of the X-rayunit, the power must be reduced for long scans.The development of multislice detector systemshas practically excluded this limitation, sincethese detector units make much more efficientuse of the available tube power.

• ShieldingEvery CT scanner is equipped with grids, collimators,and filters to provide shielding against scatteredradiation, to define the scan slice, and to absorbthe low-energy portion of the X-ray spectrum.Thus, both the patient and the examiner receivelittle scattered radiation.

Data acquisition component

• DetectorThe detector unit plays a special role in theinteraction of the CT components. It converts theincident X-rays of varying intensity into electricsignals. These analog signals are amplified bydownstream electronic components and convertedto digital pulses. Over time, certain materials haveproven very effective in the utilization of X-rays.For example, Siemens uses Ultra Fast Ceramic(UFC™) Detectors, which, due to their excellentmaterial properties, dramatically improve imagequality without an increase in X-ray dose.

Scanning unit =gantry

Data acquisitionunit = detector

X-ray unit =tube

Rotation ofX-ray unit anddetector

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Patient table

Clinical Use of CT

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CT in general clinical use

Major technological and clinical advances in recentyears have made CT scanners a standard examinationtool for many patient indications. Siemens’ CT scannersexclusively deliver the exceptional spatial and temporalresolution physicians need. Additionally, Siemensdeveloped specific software applications to streamlineclinical workflow from acquisition to postprocessingand reporting, thus providing physicians andtheir patients with ultimate clinical solutions forcardiovascular CT, oncology, neurology, and routineimaging such as chest CT. What’s more, Siemens CTscanners are not only used in hospitals or privatepractices. They are also the preferred tools of manyof the world’s clinical research facilities.

CT-Angiography (CTA)

CT-Angiography enables the display of vascularstructures aided by the injection of a contrast medium.The introduction of multislice CT scanners has madeit possible to display the entire vascular system withmaximum contrast enhancement in extremely shortscan times. Image postprocessing enables a gooddisplay of the entire vascular system. Even smallvascular exits and origins (branches) and embolismsor dissection membranes can be visualized. Thephysician can retrospectively select any projectionand generate three-dimensional images, e.g. forsurgical planning.

Clinical benefits of CT at a glance

• Excellent image quality for confident diagnosis.

• Intuitive vessel analysis and treatment planning.

• Enhanced solutions for confident assessment ofcancer patients, providing accurate informationfor diagnosis, staging, and follow up for a wide range of tumors.

• Speed and high image quality needed for a fast assessment of ischemic and hemorrhagic strokeand brain tumors.

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When is a CT examination indicated?

Here are several examples of CT examinations:

• Head • Abdomen• Neck • Extremities• Thorax • Spine

Head

Head, general/brain

Eye socket

Sella turcica

Petrous bones

Paranasal sinuses

Circle of Willis

3D cranial, facial bone

Thorax

Interpleural space

Thorax high resolution

Thoracic vessels

Pulmonary vessels

Heart

Abdomen/pelvis

Liver

CT-Arterioportography (CTAP)

Pancreas

Kidneys, biphase

Adrenal glands

Renal arteries

Abdominal vessels

Small pelvis

Vessels, pelvic/lower extremity

Neck

Cervical soft tissue

Carotids

Spine

Cervical spine

Thoracic spine

Lumbar spine

Extremities

Shoulder joint

Hip joint

Wrist bone

Knee joint

Foot

1974

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First CT System –SIRETOM

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Sequential CT

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In 1974, Siemens was the first medical equipmentmanufacturer worldwide to introduce a CT system –SIRETOM, the first head scanner. Later sequentialCT systems produced cross-sectional images of theentire body by scanning a transverse slice of thebody from different angular positions while the tubeand detector rotate 360° around the patient with thetable being stationary. The image is reconstructedfrom the resulting projection data. After each scanningsequence, the table moves a little bit along thelongitudinal axis of the body (z-direction) beforethe next scan is taken.

If the patient moves during the acquisition, however,the data obtained from the different angular positionsare no longer consistent. The result: the image isdegraded by motion artifacts and may be only oflimited diagnostic value. This tomographic techniqueis not suitable for the diagnosis of anatomical regionswith automatic movement such as the heart orthe lung.

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z-direction

Direction of patient transportafter each scanning sequence

Path of rotating gantry(tube and detector)

1987

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First Spiral CT –SOMATOM Plus Classic

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Spiral CT

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Siemens introduced SOMATOM Plus Classic, the firstSpiral CT system for routine clinical use, in 1987.Spiral CT is a technical advancement of ComputedTomography. Often referred to as “volume scanning“,it uses a different scanning principle in comparisonto sequential CT: the patient on the table is movedcontinuously through the scan field in the longitudinalaxis of the body (z-direction), while the gantryperforms multiple 360° rotations. Thus, the X-raytraces a spiral around the body, producing a datavolume. This volume is created from a multitudeof three-dimensional picture elements, i.e. voxels.

Software applications enable the clinical use of SpiralCT even for regions that are subject to involuntarymovements, such as the lung.

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z-direction

Direction of continuouspatient transport

Path of rotating gantry(tube and detector)

1998

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First Multislice CT –SOMATOM Volume Zoom

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Multislice Detector

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With SOMATOM Volume Zoom, Siemens introducedits first multislice CT scanner in 1998. Having multipledetector slices, multislice CT detectors utilize radiationdelivered from the X-ray tube more efficiently thansingle slice detectors. By simultaneously scanningseveral slices of the body, the scan time can be reducedsignificantly and the smallest details can be scannedwithin practicable scan times.

In the adaptive array detectors used by Siemens,the slices inside the detector are very narrow,becoming wider as one moves toward its outer edgesin the longitudinal axis of the body (z-direction).A combination of collimation and electronicinterconnection provides considerable flexibilityin the selection of slice thickness. At the sametime, the space required by the detector septa, andtherefore the unused space, is minimized.

Multislice CT enables a wide range of clinicalapplications from 3D to perfusion imaging toCT fluoroscopy.

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Single slice CTs have only one detector slice in thedirection of the longitudinal axis of the patient(z-direction), while multislice CTs have multipledetector slices, scanning several slices of the bodyat the same time.

16-slice spiral acquisition.

X-ray tube

Tube collimator

Collimated slice

Detector collimator

1-slicedetector

16-slicedetector

Single slice spiral acquisition.

STRATON X-ray Tube

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Conventional X-ray tubes use a rotating anodemounted in a vacuum. The limited heat exchangebetween the anode and the cooling oil results in aslow cooling rate and consequently in a build up ofthe anode heat. Thus, large anodes are requiredthat are capable of storing the high amounts of heatproduced during X-ray exams.

Siemens’ STRATON X-ray tube, on the other hand,provides innovative direct oil cooling of the anodewith ball bearings located outside the vacuum.Similar to Electron Beam CT, an electron beam isshaped and controlled by an electromagnetic field,all within the X-ray tube assembly. This technologyensures an extremely high cooling rate, resulting inan exceptionally fast rotation time. In addition, theinner tube assembly is significantly smaller thanthose used in conventional X-ray tubes, resulting ina slim tube design.

Since the discovery of X-rays, engineers haveceaselessly been trying to increase the heat storagecapacity of X-ray tubes in order to make them faster.In 2003, Siemens has set a benchmark with itsrevolutionary STRATON® technology, which is basedon direct cooling of the X-ray unit.

STRATON X-ray tubeand mobile phone

shown in comparison.25

Cathode

Anode

Vacuum

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Cooling oil

Cathode Anode

Cooling oil

Heat

1

2

Conventional anode heatsup quickly and cools downonly slowly after exposure.

Due to fastest anode cooling,STRATON never accumulatesheat during exposure.

2005

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First Dual Source CT –SOMATOM Definition

Dual Source CT

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In 2005, Siemens revolutionized the world of CTwith the introduction of SOMATOM Definition.What makes this new CT scanner so special is itsnew technology, which is called Dual Source CT.It is based on the addition of a second X-ray unit anda second detector. As a result, Dual Source CT offersunprecedented image quality and detail at lowestradiation exposure while ensuring substantiallyincreased diagnostic speed and confidence –allowing physicians to scan every heart at any heartrate. What’s more, Dual Source CT provides one-stopdiagnoses for most patients regardless of size,condition, and heart rate, which is a key pre-requisiteto make it a sophisticated tool in acute care.

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Patient table

Gantry

Detector 1

X-ray unit 2

X-ray unit 1

Rotation ofX-ray unit anddetector

Detector 2

Rotation ofX-ray unit anddetector

Portfolio of Siemens CT Solutions

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Siemens offers the right scanner for any medicalfacility from smaller practices to hospitals to researchfacilities and to examine medical conditions fromhead to toe.

Siemens’ SOMATOM family comprises the followingCT scanners:

SOMATOM Spirit – Join the World of CT

SOMATOM Spirit is the ideal CT scanner for smallerpractices, as it is cost-efficient and needs only littlespace.

SOMATOM Emotion – Efficiency in CT

SOMATOM Emotion is an excellent choice for biggerprivate practices or smaller hospitals. It is a greatchoice to meet everyday needs in CT.

SOMATOM Sensation – Performance in CT

Due to its excellent performance, SOMATOMSensation is well-established in both clinical routineand advanced research.

SOMATOM Definition – Excellence in CT

SOMATOM Definition is the latest revolution in CT.Its new Dual Source CT technology promotespioneering new clinical opportunities at the highestlevel, making it the ideal choice for bigger hospitalsand research facilities.

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SOMATOM EmotionSOMATOM Spirit

SOMATOM DefinitionSOMATOM Sensation

On account of certain regional limitations of sales rights

and service availability, we cannot guarantee that all

products included in this brochure are available through

the Siemens sales organization worldwide. Availability

and packaging may vary by country and is subject to

change without prior notice. Some/All of the features

and products described herein may not be available in

the United States.

The information in this document contains general

technical descriptions of specifications and options as

well as standard and optional features which do not

always have to be present in individual cases.

Siemens reserves the right to modify the design,

packaging, specifications, and options described herein

without prior notice. Please contact your local Siemens

sales representative for the most current information.

Note: Any technical data contained in this document

may vary within defined tolerances. Original images

always lose a certain amount of detail when reproduced.

The statements contained herein are based on the actual

experience of Siemens customers. Siemens maintains

data on file to support these claims. However, these

statements do not suggest or constitute a warranty that

all product experience will yield similar results. Results

may vary, based on the particular circumstances of

individual sites and users.

Please find fitting accessories:

www.siemens.com/medical-accessories

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HeadquartersSiemens AG, Medical SolutionsHenkestr. 127, D-91052 ErlangenGermanyTelephone: +49 9131 84-0www.siemens.com/medical

Contact AddressSiemens AG, Medical SolutionsComputed TomographySiemensstr. 1, D-91301 ForchheimGermanyTelephone: +49 9191 18-0

© 03.2006, Siemens AG

Order No. A91100-M2100-3420-1-7600

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CC CT 00162 WS 03065.