computed tomography machine

Medirays Corporation

The Computed Tomography system - GE Prospeed series 6.1

THE COMPUTED TOMOGRAPHY SYSTEM

1. Introduction

Computed tomography is a medical imaging technique, which employees tomography, where

digital geometry processing is used to generate a three dimensional image of an object from a

large series of two dimensional image taken around a single axis of rotation. In computed

tomography, the image is made by viewing the patient via x- ray imaging from numerous angle,

by mathematically reconstructing the detailed structures and displaying the reconstructed

image on a video monitor.

Fig41. GE Prospeed CT system

2. History

At the Annual Congress of the British Institute of Radiology, in April of 1972, G.N.Hounsfield, a

senior research scientist at EMI Limited in Middlesex, England, announced the invention of a

revolutionary new imaging technique, which he called “computerized axial transverse

scanning.” The basic concept was quite simple a thin cross section of the head, a tomographic

slice, was examined from multiple angles with a pencil-like x ray beam. The transmitted

radiation was counted by a scintillation detector, fed into a computer for analysis by a

mathematical algorithm, and reconstructed as a tomographic image. The image had a

remarkable characteristic, one never before seen in an x ray image: it demonstrated a

radiographic difference in the various soft tissue; blood, gray matter, white matter,

cerebrospinal fluid, tumors, and cerebral edema all appeared as separate entities. The soft

tissues could no longer be assigned the physical characteristics of water. The computer had

changed that concept.

Computed tomography has had many names, each referring to at least one aspect of the

technique. Two of the more popular names are computerized axial tomography (CAT) and



computed (computerized) tomography (CT). CT is currently preferred as computed

tomography.

Like most great discoveries, CT was the end product of years of work by numerous

investigators. An Austrian mathematician J.Radon, working with gravitational theory, proved in

1917 that a two or three dimensional object could be reproduced from an infinite set of all its

projections. Thus, the mathematical concept was established 55 years before the production of

a commercial CT scanner. Workers in several unrelated fields were all struggling with a similar

problem. In 1963 understood the concept of computed tomography and built laboratory

models. Kuhl and Edwards in 1968 built a successful mechanical scanner for nuclear imaging,

but did not extend their work into diagnostic to put a CT system together and demonstrate its

remarkable ability.

Fig 42. GE prospeed CT machine

3. Principles of CT:

It is basically a technique of X-ray photography by which a single plane of a patient is scanned

from various angles in order to provide a cross-sectional image of the internal structure of that

plane. The principal of CT is the measuring of the spatial distribution of physical material to be

examined from different directions and to compute superposition free images from this data. It

is basically a technique of X-ray photography by which a single plane of a patient is scanned

from various angles in order to provide a cross-sectional image of the internal structure of that

plane.

For conventional radiography, the relative distribution of X-ray intensities is what is being

measured. Figure 1 demonstrates how this is achieved. An X-ray source of intensity Io is used

to send uniform intensity X-rays through a patient. The X-rays then exit the other side with an

intensity of I(x, y) and interact with a radiography film sheet. The exiting X-rays are attenuated

by the varying material densities that they pass through. The different paths through the



material will attenuate the X-rays by varying amounts, based only on the mass attenuation

coefficient (μ), since the distance (d) is the same on all point of the radiography film. It is this

variance that is recorded by the two-dimensional radiography film and is shown as lighter or

darker contrasts.

Fig43. Typical radiography concept

This process has some limitations. Specifically, the image captured is a two dimensional

representation of three dimensional anatomy. As a result, structures are overlapping on the

image and make positional details hard to see. Another limitation is that the mass attenuation

coefficients for tissues do not vary greatly. Thus, it is difficult to resolve some internal

structures. However, computed tomography (CT) provides solutions to these limitations.

The principle of CT is to have many measurements of attenuation through the plane of a finite-

thickness cross section of the patient. Figure 2 shows this concept. An X-ray source is used to

scan a patient along this plane, while a detector on the opposite side measures the attenuated

X-rays along this plane and the computer records this capture. Once the patient has been

scanned from one side of the plane to the other side, both X-ray source and detector rotate

around the patient by a predetermined amount and the translational scan is repeated. The

internal components of the patient are interpreted by the computer as a group of small

volumes, each with their own average mass attenuation coefficient. These volumes are called

voxels (like pixels on a TV screen). The smaller the voxel volume, the higher the resolution of

the image.

Fig44. CT cross-sectional measurement



Fig45.The CT scanner

In order to generate an image of the cross section, the computer must attempt to calculate the

average mass attenuation coefficients (μ) of each of the voxel volumes. This could be

determined algebraically with a very large number of simultaneous equations, however a

simpler method called filtered back-projection was used in the early CT scanners and remains in

use today. X-ray scans are collected in sets called projections, which are made across the

patient in a particular direction in the section plane. To reconstruct the image from the X-ray

measurements, each voxel must be viewed from multiple different directions. A complete data

set requires many projections at rotational intervals of 1° or less around the cross section. Back-

projection effectively reverses the attenuation process by adding the attenuation value of each

X-ray in each projection back through the reconstruction image. This requires a significant

computer power to quickly generate the patient image. Because this process initially generates

a blurred image, the data from each projection are mathematically altered (filtered) prior to

back-projection to eliminate the blurring.



CT generations

The general classification of computed tomography (CT) scanners based upon the arrangement

of components and the mechanical motion required to collect the data. The term generation

has been applied because of the order in which the CT scanner designs have been introduced,

and each has a number associated with it. However, one should not assume that a higher

generation number necessarily means a higher performance system.

First generation: In the first CT scanner design, a single X-ray

source and a single X-ray detector cell collect all the data for

a single slice. The source and detector are rigidly coupled and

the pencil beam is translated across the patient to obtain a

set of parallel projection measurements at one angle. The

source/detector pair is then rotated slightly and a

subsequent set of measurements are obtained during a

translation past the patient. This process is repeated once for

each projection angle. Because of the translation and

rotation process, this geometry is referred to as a

translate/rotate scanner.

Fig46. First generation

Second generation: Because the X-ray source emits radiation

over a large angle, the efficiency of measuring projections

was greatly improved by using multiple detectors. The

detectors all lie within the scan plane but are not necessarily

contiguous nor do they span the entire diameter of the

object. The source and the array of detectors are translated

as in a first generation system, but since the beam measured

by each detector is at a slightly different angle with respect

to the object, each translation step generates multiple

parallel ray projections. Because multiple projections are

obtained during each traversal past the patient, the 2nd

generation scanner is significantly more efficient and faster

than the original 1st generation scanner. This generation is

also referred to as a translate/rotate scanner.

Fig47. Second generation

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Third generation: With improvement in

detector and data acquisition technology, it

was possible to design a detector array with

enough, high spatial resolution cells to allow

the simultaneous measurement of a fan-beam

projection of the entire patient cross-section.

With such a large detector, it is no longer

necessary for the detector-tube assembly to

translate past the patient. Instead, the tube-

detector assembly simply rotates around the

object. The imaging process is significantly

faster than 1st or 2nd generation systems.

However, very high performance detectors are

needed to avoid ring artefacts and the system

is more sensitive to aliasing than 1st or 2nd

generation scanners. Because the tube and

detector both rotate, this generation is often

referred to as rotate/rotate scanner geometry.

Fig48. Third generation

Fig49. Internal view of gantry

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Fourth generation: Contemporary with the development of viable third generation,

rotate/rotate, systems and to avoid the sensitivity to ring artefacts, a design was developed

using a stationary detector ring and a rotating X-ray tube. Because the reduced motion seemed

consistent with a reduction in complexity, this geometry is known as the fourth generation. The

stationary detector requires a larger acceptance angle for radiation, and is therefore more

sensitive to scattered radiation than the 3rd generation geometry. Fourth generation

geometries also require a larger number of detector cells and electronic channels (at a

potentially higher cost) to achieve the same spatial resolution and dose efficiency as a 3rd

generation system. This system is sometimes referred to as a rotate-stationary or rotates only

geometry.

Fig50. Fourth generation

Several other CT scanner geometries which have been developed and marketed do not

precisely fit the above categories. However, there is no agreed-upon generation designation for

them. In a fourth generation scanner, the detector ring is outside the circular path of the X-ray

source. A CT system design was developed in which a circular detector ring is inside the source

trajectory. This reduces the size of the detector array and may lead to a more compact system.

In this system, the detector array nutates so that the detectors do not obstruct the X-rays as

they pass from the source to the object (nutating detector ring). In some texts, this is referred

to as a fifth generation system. It can also be called a rotate-nutate scanner.

The cine CT system has no mechanical scanning motion. In this system both the X-ray detector

and the X-ray tube anode are stationary. The anode, however, is a very large semicircular ring

that forms an arc around the patient scan circle, and is part of a very large, non-conventional X-

ray tube. The source of X-rays is moved around the same path as a fourth generation CT

scanner by steering an electron beam around the X-ray anode. Because the electron beam can

be moved very rapidly, this scanner can attain very rapid image acquisition rates. In the

literature, this system has been referred to variably as fifth generation and sixth generation. It

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has also been described as a stationary-stationary scanner. The terms millisecond CT, ultrafast

CT and electron beam CT have also been used, although the latter can be confusing since the

term suggests that the patient is exposed to an electron beam.

Fig51. Slip ring technology

Fig52. Contacts on the slip ring

Slip-ring technology has had a great impact on CT system performance and utilization. Whereas

most previous conventional CT systems used a cable-take-up mechanism to deliver electrical

power to the X-ray tube (and could rotate through perhaps 400-600 degrees before it had to

stop), use of a slip-ring allows the continuous rotation of the X-ray tube (and the detector

Slip rings

Contacts

Varying

thickness




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assembly if appropriate). While not as fast as the cine CT scanner described above, these slip-

ring scanners can attain sub-second image acquisition rates, zero interscan delay, and are

compatible with helical scanning or spiral CT scanning (see helical CT scanner). They are

generally referred to as slip-ring versions of their respective (e.g. third or fourth) generations.

Speed and spatial resolution have been significantly improved recently with the development of

multisection CT technology. The multisection capability has been created by dividing each

detector element into several smaller sub-elements. Each sub-element has its own complete

data acquisition electronics.

Fig53. Internal view of gantry

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Table 3: Characteristics of various generations of CT



CT Prospeed systems:

The CT prospeed system is a continuous rotation gantry type CT scanner which uses low voltage

slip rings for power and signal transmission. The different units of a CT scan machine are

Gantry

Patient table

Power distribution unit

Operator console

Stabilizer

The basic system is equipped with a magnetic optical disk unit on the operator console,

additionally customer can also purchase advanced windows diagnostic console and Ethernet

interface.

Data Processing System (DPS):

Central processor (data storage unit)

Image/ reconstruction processor

Interface for operator and component.

The data processor system consists mainly five boards as follows:

1. CPW (Central Processor of DPS) :-

It controls data transfer between storage units (hard disks) and memory devices (on

IPU2 board).

It also controls entire scan sequence and sends required information to relevant

components and receives status information from those components via MISC2 board.

2. IPU2 (Image/Reconstruction processor):-

It contains 64 bit microprocessor and 96Mb memory which is used for raw data during

high rate scans (helical scans) and for image reconstruction.

The processor does reconstruction for stored data on memory according to the CPW

processor instruction.

3. DISP2 (Image display):-

It has an image frame buffer and image overlay function to generate video display data

which is converted from digital to analog.

It also contains DAS data buffer for receiving DAS data from DAS IF board and sending it

to IPU2 board.

4. MISC2 (Interface between CPW and other boards)

It provides the no of interface between CPU and other components such as touch panel,

controller, multiformat camera, key board trackball, scanning station (TGP board on

gantry) or scan panel switches/LEDs



5. SPBU (Back projection)

It operates as a back projection unit under IPU2 board control

6. IPA (Image reconstruction processor/accelerator)

It is used instead of SPBU for fast image processing and reconstruction.

Up to two IPA boards can be installed on the OC.

Storage units:

A 3.5inch hard disk holds operating system software, several system parameters, calibration

data, patient image data and raw data. A 5 inch MOD to load system software are archived

image data, raw data and to save system parameters. The floppy disk drive is used for loading

option software, or using the boot floppy disk.

SCAN STATION:

1. GANTRY:

It contains x-ray tube, generator, collimator, detector, DAS, table gantry processor(TGP

board)

The axial drive motor, rotates the x-ray tube, generator, collimator, detector, DAS assembly

during axial scan.

The gantry hydraulic pump and cylinders can tilt the gantry frame +/- 25° from vertical.

2. TABLE:

It is a unit of CT machine where patient lies down to take a scan.

A stepping motor moves the table in longitudinal direction (in/out) and a hydraulic pump

raises or lowers (up/down) the table.

3. X-RAY GENERATOR:

The x-ray generator supplies DC power to x-ray tube to make x-ray exposure.

It contains circuit board for kV control, rotor control, filament, current control, and overall

control of the generator system

It contains HV tanks, invertors for kV generation, rotor power module including an inverter

4. COLLIMATOR:

It consists of removable bowtie filter and the aperture assembly

The filter shapes the x-ray beam intensity. The aperture regulates x-ray beams slices

thickness to 1mm, 2mm, 3mm, 5mm or 10mm at the isocentre.



5. DETECTOR:

It converts x-ray intensities which are received by the detector into electrical signals.

It uses total of 813 channels.

6. DAS(data acquisition system):

The data acquisition system charges the signals from the detector, then converts , digitizes

and transfer the data to the data processing system.

7. X-RAY TUBE:

The XG subsystem provides DC high voltage, together with filament heating current, to

the x-ray tube.

It also provides power for anode rotation.

X-ray need 120 kv and output currents as 40mA, 60mA, 80mA, 100mA, 130mA, 160mA.

The Sytec system uses a rotating anode x-ray tube.

The heat exchanger and x-ray tube are mounted separately on the gantry.

The tube contains an anode (target), cathode as filament, rotor, stator coil, and

temperature sensors and the anode rotates at 10,000 revolutions per minute.

The stator coil produces the magnetic field that induces a current in the copper rotor.

The stator coils and rotor work as an induction motor.

The filament is the source for electrons in the x-ray tube.

The tube current increases as the filament current increases.

The anode is biased positive with respect to ground and the cathode is biased negative.

To get 120 kV high potential x-ray voltage, during an exposure, they are biased to +60 KV

and -60 KV

Fig54. Different CT tubes



PDU (POWER DISTRIBUTION UNIT):

PDU receives the network power supply and distributes electric power to all sub-systems of CT

systems.

PDU is available in two forms:

1. P9180AB/AF: It provides regulated 550VDC output.

2. 2121798: It provides non-regulated 700VDC output.

The PDU provides

1. Regulated (550VDC) or non-regulated (700 VDC) for inverters (kV and rotor) of x-ray

generator and to slip rings.

2. From slip rings it goes to inverter of cathode and anode and CTVRC

3. 200 VAC, 3-Φ for servo amplifier and gantry.

4. 100VAC, 1-Φ for operator console.

5. 115VAC, 1- Φ for table, gantry tilt, the control components like TGP boards and IGBT

driver circuits.

6. The output of IGBT is AC which goes to HV tank and in the HV tank it is stepped up using

transformer and rectified to DC. This DC supply is then given to the x-ray tube.

WARM-UP ROUTINE:

The system requires warm-up routine to warm-up the x-ray tube just after the power on prior

to starting the first scan or when 3 hours have elapsed since the last scan. The warm-up routine

also should be performed before performing phantom calibration which updates the calibration

files (CAL files).

The following series of scans are performed during the warm-up sequence.

Two scans without data collection - (2.0 sec, rotate, 1mm thickness, 80kV, 80mA)

Four scans without data collection - (2.0 sec,rotate,1mm thickness,120kV, 100mA)

15 scans without data collection - (2.0 sec,rotate,1mm thickness,120kV, 200mA)

1 scan with data collection – (3.0 sec, stationary,10mm thickness,120kV, 60mA)

Fig55. Interface of TGP board with OC



TGP Board:

It is the subsystem controller of gantry

It has two microprocessor that receive commands and data from the scan processor and

execute corresponding task.

Both processors communicates through serial links

TGP board issues commands to and receive status from the components it controls such

as axial drive control, tilt control, cradle in/out, table elevation, collimator control, das

control, hv on control.

Filament Current Control:

The current is adjusted by the variable resistor and is regulated by CVT.

There are rough adjustment resistors to adjust current.

The sensibility of the rough adjustment is 11 times of the fine adjustment.

Adjust the variable resistor which is set in series with the variable resistors for rough

adjustment and fine adjustment, and the current at all technique can be adjusted at the

same time.

Disconnect the connector of the adjusting panel and connect the other variable resistor to

the connector, then the current can be adjusted from external.

The filament current detecting circuit operates when more than 0.18 A current flows

through the primary side of the filament transformer.

Scan Operation: This section describes the system operating during scan. Each scan sequence has the following three phase.

1. Scan preparation

That is to set the scan parameters. It includes kv, mA, slice thickness, scan time, slice interval, and cradle in out.

Fig56. Scan Preparation



2. Data collection

That is to perform a scan. As scan is initiated data collection is initiated after pressing the

start button.

Prior to the actual X-ray exposure, the system gathers 64 view of the electronic offset data

from the DAS. It uses these offset to correct the actual X-ray data.

The system performs a full 360 degree scan in clockwise and counter clockwise at the 3 or

5 sec and rate, and collects 648 views of data per scans.

It can also perform a 228 degree partial scan in same clock and counter clock wise at the 2

second rate, and collect 410 view of data per scan. The sampling rate depends upon the

scan speed: 3msec/view for 2 or 3 second scan, 5 ms/view for 5 second scan.

3. Data processing

As the data is collected in the DAS the DAS memory transfers the collected data (raw data)

to the console.

The das memory outputs raw data to the FPU and on the hard disk. The FPU process the

data and outputs it to the back projection unit.

The BPU performs the back projection and send it back to FPU.

The FPU performs the post-processing and produces the image data.

The FPU compresses the image data, stores it on the hard disk.

When auto mode display is selected, the FPU transfers the image data to the display

image on the CRT monitor.

Image Reconstruction: The 3 phases of CT Image Reconstruction are as follows

(1) Scan Phase CT machines use various methods of acquiring the necessary projection data to produce a CT image. These methods are classified in terms of their scan geometry about the object.

Fig57. Scan phase in image reconstruction



For example, in medicine, 2nd generation CT systems are generally used which operate a

translate/rotate scan geometry about the object, whereas most industrial systems use a 3rd

generation configuration involves the use of cone beam projections and the object under study

being placed on a rotating manipulator. This enables the system to collect the many angles of X-

ray attenuation data or X-ray projections needed to perform CT reconstruction.

Fig58. Slice images

(2) Image Reconstruction

In this phase specialised algorithms are used to reconstruct a 2D image from the set of X-ray

projections, known as the sinogram, produced during the scan phase. In other words,

complicated algorithms are used to reconstruct the distribution of the X-ray attenuation data to

produce a digital image.

The most common algorithm used for this process is the Filtered Back Projection method,

which calculates from this set of 1D sinogram lines a reconstructed 2D image.

Back projection is the mathematical process of obtaining the digital image from the projection

data or sinogram, but if it is not filtered in some way, results in a very noisy image, hence the

use of Filtered Back Projection

The CT image is now digital in the form of a matrix of pixels, and a part of the reconstruction

process is the calculation of CT numbers for each image pixel

The CT numbers are calculated from the X-ray attenuation data for each individual voxel first

calculated in the reconstruction process.

X-ray attenuation depends on both the density and atomic number (Z) of materials and the

energy of the X-ray photons. Therefore, the density of the materials determines the CT

numbers. So for all practical purposes, the CT image is an image of the densities of the material.



(3) Visible Image Formation

In this phase the digital image, consisting of a matrix of pixels with each pixel having an

assigned CT number is converted into a visible image represented by different shades of grey.

Each number represents a shade of grey with +1000 (white) and -1000 (black) at either end of

the spectrum.

Patient Preparation:

Patients should wear comfortable, loose fitting clothing for their CT exam. Patient preparation

for a CT examination involves removing any articles of clothing or jewellery that might degrade

the CT images, such as belts, earrings, bras, glasses, dentures, hairpins, etc. Zippers and snaps

common in many clothes can also cause image degradation. In some cases, the patient may be

asked to wear a patient gown (such as CT imaging of the body).

Many CT examinations require the oral or intravenous administration of a contrast agent, a

liquid material that enhances the images of the organs and/or blood vessels. CT imaging

examinations that require the patient to receive iodine contrast injection may cause slight,

temporary discomfort while the intravenous needle is placed.

Patients should inform the radiologist or technologist if they have a history of allergies

(especially to medications, previous iodine injections, or shellfish), diabetes, asthma, a heart

condition, kidney problems, or thyroid conditions.

Also, many CT exams require the patient to hold their breath several times. This helps to

eliminate blurring from the images, which can be caused by breathing or other patient motion.

Pregnant women should not have a CT exam or any x-ray examination, especially if the woman

is in her first trimester (first of three-3 month periods of pregnancy). Also, patients are

instructed to wait for 24 hours after receiving the CT contrast injection before breast feeding

again.



Advantages

As mentioned in previous sections, CT imaging provides detailed views of soft tissues, bones

and blood vessels. It can eliminate invasive exploratory surgeries such as laparotomy,

thoracotomy, and invasive endoscopy such as colonoscopy. It is a non-invasive diagnostic tool

which is considered highly accurate, fast, simple, and cost effective. CT scan can identify

internal bleeding and injuries which are essential for treatment of trauma patients. It is also

frequently used in assisting surgical biopsies for confirmation of certain diseases.

Disadvantages

Despite the many benefits mentioned above, several hazards and disadvantages are present

with CT imaging. One of the main hazards of CT imaging is the risk of allergic reaction

(nephrotoxicity) to the contrast agent which may cause itching, hives or swelling of body parts.

CT imaging involves exposure to small amount of ionized radiation which is considered a hazard

for pregnant women and children. CT scanning may also involve uncomfortable body posture in

order to obtain imaging of the desired body part. In addition, due to the physical shape of the

CT equipment, claustrophobic patients may experience anxiety. Furthermore, early detection

of diseases with CT scan may lead to more aggressive treatments such as chemotherapy or

radiotherapy which may cause more serious side effects than if diseases were diagnosed based

on symptoms. Early detection of diseases is also not 100% accurate. Hence, it may lead to

confirmatory procedures, such as invasive biopsies, that in fact may not be necessary.



Next generation Nano CT system:

Fig59. Next Generation Nano CT



In 1991, Ge Wang produced the first paper on spiral cone-beam computed tomography (CT),

now an imaging technique used in the mainstream of the medical CT field. Today, Wang,

known as a pioneer in this field, and his colleagues have been awarded more than $1.3

million from the National Science Foundation (NSF) to develop the next-generation nano-CT

imaging system, which promises to greatly reduce the required dose of radiation. Virginia

Tech and Xradia, a leading nano-CT company, are also collaborating on the project with a

cost-sharing investment of close to $800,000. CT is an imaging method that shows objects by

sections or sectioning, through the use of x-ray waves and computer processing.

X-ray nano-CT is a cutting edge imaging tool, Wang said, but a long-standing barrier to

realizing its full potential is its inability to precisely reconstruct an interior region of interest

within a larger object from purely local projections.

Wang, the Samuel Reynolds Pritchard Professor of Engineering at Virginia Tech, has a

scholarly record of achievements in the imaging world. More than 1000 scientific citations are

attributed to his groups pioneering efforts. In 2002, for example, he and his research group

pioneered another highly sensitive imaging procedure called bioluminescence tomography

(BLT). One application of the in vivo molecular imaging technology became the identification

of tumors in live animals.

As an additional example, in 2007 he and his collaborators, Yangbo Ye of the University of

Iowa and Hengyong Yu, who is the associate director of Wang CT lab, patented a novel x-ray

imaging method called interior tomography.

Interior tomography, Wang said, was a first step towards overcoming the long-standing

barrier to realizing the full potential of x-ray nano-CT. Despite the ability of this cutting-edge

imaging tool as a non-destructive, non-invasive recorder of information, it cannot precisely

reconstruct an interior region of interest within a large object from purely local projections,

Wang said. And, when used in medicine, a patient is subjected to a radiation dose that must

be increased dramatically to obtain improved resolutions.

Wang suggested to the NSF that the combination of X-ray nano-CT and interior tomography

will provide a versatile nano-imaging tool that can visualize fine features within a larger

object, and use a much lower radiation dose and in much less time. This new work is the

foundation of the NSF project.

Working with Wang on this NSF grant are Chris Wyatt, associate professor of electrical and

computer engineering, Linbing Wang, associate professor of civil and environmental

engineering, and Yu, all at Virginia Tech. Also, David Carroll, associate professor of physics at

Wake Forest University, is a member of the team. On the industrial side, the key collaborators

are Steve Wang, S. H. Lau and Wenbing Yun.

Together, they believe they can construct this next generation of a nano-CT imaging system

that will provide images that will reveal deeply imbedded details, including sub cellular



features. And, they believe they can handle a sample that is ten times larger than what is

currently available, and at much reduced radiation dose, Wang explained.

Wang, director of the Virginia Tech-Wake Forest University School of Biomedical Engineering

Sciences' biomedical imaging division is also the founding editor-in-chief of the International

Journal of Biomedical Imaging. He is the associate editor of the Institute of Electrical and

Electronic Engineers (IEEE) Transactions on Medical Imaging and others.

SBES is part of the University Institute for Critical Technology and Applied Science (ICTAS).

ICTAS has already developed a state-of-the-art nanoscale characterization and fabrication

laboratory with capabilities on par with the best nanotechnology labs in the world. With his

high-end 500 nanometer micro-CT system, newly funded by the National Institutes of Health

(NIH), Wang is making efforts to build an advanced multi-scale CT facility in synergistic

combination with the existing university resources as shown in the following chart.

We are realizing our dream to establish the world’s most advanced comprehensive multi-

scale and multi-parameter CT facility, Wang said. The use of the facility will be available to

other universities and industry.

An academic partnership already exists between Virginia Tech and Xradia. Xradia is already in

talks with Virginia Tech about commercializing the next generation nano-CT system.



Applications of CT:

CT can provide detailed cross sectional images and diagnostic information for nearly every

part of the body including:

The brain, vessels of the brain, eyes, inner ear, sinuses.

The neck, shoulders, cervical spine and blood vessels of the neck.

The chest, heart, aorta, lungs, mediastinum.

The thoracic and lumbar spine.

The upper abdomen, liver, kidney, spleen, pancreas and other abdominal vessels.

The pelvis and hips, male and female reproductive system, bladder, and GI tract.

The skeletal system including bones of the hands, feet, ankles, legs and arms and jaws.

Fluoro CT’ is more like a video camera (or x-ray fluoroscopy) and allows acquisition and

immediate display of up to 9 images per second. It is used to guide a number of minimally

invasive, micro-therapy procedures:

Drainage of fluid collections such as cysts, abscesses (pus), lymphoceles (lymph fluid),

bilioma (bile), haematomas (blood), for example, to remove fluid from an infection or

wound.

Diagnostic biopsy to remove a tissue sample for pathologic or cytologic lab testing.

Pain therapy, for example, the injection of therapeutic agents into a spinal disk space to

alleviate pain.

Minimally invasive operation, for example, cyst removal or ablation (cutting away) of

tumours (such as brain tumours).

Dynamic study of knee or elbow motion, swallowing or study of the larynx.

CT arthrogram (injection of contrast into joint space for easier diagnosis of injury).

Guidance of embolization to stop bleeding, for example, in liver and spleen trauma

Monitor difficult endoscope placement, for example in the gastrointestinal tract



COMPARATIVE STUDY

Comparison of SIEMENS Somatom Sensation 64 CT Scanner to GE Prospeed S CT Scanner

Parameter SIEMENS Somatom

Sensation 64 GE Prospeed S

Max Generator Output Power 70 kW 24 kw

Tube Current Range 28 – 580 mA 60,80,100,130,160,200 mA

Tube Voltage Range 80, 100, 120, 140 kV 80, 120, 140 kV

Anode Heat Storage Capacity 30 MHU 2 MHU

Anode Cooling Rate 5 MHU/min 820 KHU/min

Gantry Aperture 70 cm 68 cm

Gantry Tilt ± 30° ± 25°

Rotation Time (360°) 0.33, 0.37, 0.5, 1.0 s 2, 3.5 sec

Vertical Table Range 53 – 102 cm 40 – 100 cm

Elevation Speed 2.5 – 45 mm/s 15 – 20 mm/s

Horizontal Scannable Range 1570 mm 920 mm

Maximum Table Load 450 lbs 400 lbs

Table Speed 1 – 150 mm/s 15 mm/s and 55 mm/s

Number of Slices per Scan 64 1

Number of Detector Elements 26880 635

Number of Projections 4640 648

Table 4: Comparison between Siemens Somaton and GE Prospeed S

computed tomography machine

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