alla shorokhova, "computed tomography"

COMPUTED TOMOGRAPHY

Saint Petersburg Electrotechnical University

“LETI”Student Alla Shorokhova

5104 groupHead Professor Alexander

Mikerov

Shorokhova Alla, 5104 2

IntroductionThe term "tomography“ comes from two Greek

words: τομοσ - section and γραφοσ – write (layer-by-layer study of the structure of various

objects)Types of imagingEssence: on the summary information it is

necessary to define the local information (the matter density at each section)

ApplicationThe first and most famous application of imaging is

computerized X-ray reconstructive tomography (CT)


History

The first CT scanner (a) and the first tomography of the brain (b)

a b

• 1969, Godfrey Hounsfield EMI-scanner

• 1917, Johann Radon, created a mathematical foundation tomography• 1963, Allan Cormack

• 1979, Cormack and Hounsfield were awarded the Nobel Prize "for the development of computed tomography"


Schemes of imaging

4 generations of CT scanners

1 generation1973;incremental;1 image – 4 minutes.

2 generationSeveral detectors;Imaging – 20 sec.

3 generationSpiral CT 4 generation

1,088 fluorescent sensors;Rotates only X-ray tube;0.7 seconds


Construction1. X-ray tube and a collimator2. Detectors and data acquisition system3. Tube controller4. High-frequency generator5. Built-in microcomputer6. Computer that provides data exchange with the console


Construction (2)X-ray tube with the collimation system

creates a narrow fan-shaped light beam, whose divergence angle is 30 ° -50 °

Attenuation of X-ray beam -> recorded by detectors -> electrical signals. These analog signals -> converted into digital pulses

In the CT ceramic, fluorescent and gas detectors are used

Extensive software package


Scan Modes

Conventional (incremental) CT(short pause , several minutes)

Spiral (helical) CT(helical motion of X-ray tube, reducing time and radiation exposure)


Multiple-Row Detector Spiral CTMDCT, 1992: two or more series of detectors

located around the circumference gantrywidth of the detector increases from center to edge1998: 4-row unit2004-2005: 32-, 64-,128-row units


Image reconstruction

Substance

HU

Air -1000

Fat -120

Water 0

Muscle +40

Contrast +130

Bone +400 or more

• The pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from +3071 (most attenuating) to -1024 (least attenuating) on the Hounsfield scale• Voxel is a volumetric pixel

The HU of common substances:


Three-dimensional reconstructionMaximal Intensity Projection, MIP (consists of voxels having the maximum

density)Multiplanar Reconstruction, MPR (makes it possible to reconstruct images in any projection)Surface Shaded Display, SSD (threshold value in units of HU)Volume Rendering (combination)

Figure: Typical screen layout for diagnostic software, showing one 3D and three MPR views


Example of Volume Rendering (1)Some slices of a cranial CT scan are shown

belowA volume rendering of this volume clearly

shows the high density bones.Figures: Computed tomography of human brain, from base of the skull to top. Taken with intravenous contrast medium.


Example of Volume Rendering (2)After using a segmentation tool to remove the

bone, the previously concealed vessels can now be demonstrated.

Bone reconstructed in 3DBrain vessels reconstructed in 3D after bone has been removed by segmentation


ConclusionsCT - an important component of inpatient and

outpatient care. The result of CT - a combination of powerful computer

processing with the knowledge and skills of a trained human operator.

Modern CT scanners are able to emit and collect data about the 1400 positions of the detector tube on the circle 360 °, or about 4 positions in degrees.

Technical merits of the spiral CT and volumetric reconstruction open up new prospects for medical imaging.

In 2010, so-called 4-dimensional electron tomography was created - visualization techniques of the dynamics of 3-dimensional objects in time.

Thank you for your attention!

alla shorokhova, "computed tomography"

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