Advancement in CT technology

Presented by

Nisha karna

Roll.No: 25

NISHA KARNA

ADVANCES

A. Hardware Components

• Data Acquisition Geometry (Beam Shape).
• Detector Technology.
• Multiple Detector Arrays.
• X-ray Tube Design.
• Rotation time, Collimator
• Dual energy CT scanners
• Cardiac CT
• CBCT, Flat Panel CT,Mammo CT, Portable CT….

B. Reconstrution Algorithms

C. Applications

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1.DATA ACQUISITION GEOMETRY

• As the number of detectors in a multi-row detector array increases, the beam becomes wider to cover the 2D detector array.
• Larger no. of rows in the detector array will result in a wider beam in z-axis direction (cone beam).
• Special cone beam reconstrution algorithms have been developed.

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DATA ACQUISITION GEOMETRY

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ADVANCES IN DETECTOR

• Ultrafast Ceramic

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• Solid State Flat-Panel Detector

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• Stellar Detector

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• Gemstone

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ULTRA FAST DETECTOR

• Ultrafast Ceramic is a hard yellow substances that resembles plastic and weighs about as much as gold
• It includes rare earth elements gadolinium , sulfur and other addition.
• The material is formed through the process that involves mixing, chemical reduction , sintering and pressing.

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ULTRAFAST CERAMIC

• Ultrafast Ceramic scintillator material was developed with high X-ray absorption efficiency, a fast decay behavior and low afterglow for the CT system with the highest rotation speed and the shortest integration time

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• The decay constant is 3 µ sec and is optimized for integration time of 20 µ sec in order to prevent image quality

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ULTRAFAST CERAMIC

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UFC

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ADVANTAGES

• Higher x-ray absorption efficiency
• Short afterglow
• Fast decay time
• The decay constant is nearly 3ms and its optimized for interrogation time of 20ms in order to maintain the image quality.
• UFC scintillation material is easy to handle due to its resistance to ambient air, humidity, water, temperature and numerous chemicals such as oils and solvents (other detector materials are hygroscopic and must be sealed).
• UFC is a non-poisonous material that does not contain any toxic elements as other solid state scintillation materials do, it has no adverse environmental impact.

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Solid State Flat-Panel Detector

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• It consists of a film of cesium iodide scintillator crystals that is cast onto a matrix of photographic detectors made of amorphous silicon.
• It yields ultra high isotropic spatial resolution (up to 150µm)compared with multi-detector CT (600µm) high resolution mode.
• Low contrast resolution & dose efficiency

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Stellar Detector

• Combines all the analysis electronics in a single chip.
• The converted signals can be processed digitally with no loss making it possible to produce medical images with a noticeably higher SENR than before at the same dose.

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• Reduces the image noise by 20 to 30 %

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• Delivers extremely detailed images with a spatial resolution as fine as 0.30 mm .

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Stellar Detector

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Stellar Detector

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Stellar Detector

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Gems Stone detector

• Newly developed transparent polycrystalline scintillator CT detector developed by GE .

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• Has higher sensitivity to radiation and allow faster sampling rate.

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• Used in single source ultrafast dual energy switching , promising almost simultaneous spatial and temporal registration and material decomposition.

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Gems Stone detector

• Has very low afterglow, extremely low radiation damage, very good chemical durability and uniformity.

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• Has primary decay time of only 30nsec i.e. 100 times quicker than conventional scintillators.

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• The noticeable advantage of gemstone detector is the improved spatial resolution

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Gems Stone detector

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Gems Stone detector

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Gems Stone detector

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Arrangement of detector

• The current MDCT scanners acquire 2, 4, 6, 8, 10, 16 simultaneous sections. Scanners with 32, 40, 64, 128, 256 & 320 slice CT are now also available.
• Detector array design in MDCT varies among vendors.
• This is achieved by collimating & adding together the signals of neighbouring detector rows.

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• Three types of detector arrays:
• Matrix Array (Linear, Uniform)
• Adaptive Array (Non–Uniform or Variable)
• Hybrid Array

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Matrix Array (Linear, Uniform)

• A detector design that is subdivided into equal elements, or portions, is called “Uniform,” “Matrix,” or “Mosaic”.

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• Mosaic detectors have elements that are all of uniform size. The thickness of the sections that can be generated from these detectors is a multiple value of the uniform size of the detector element.

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Adaptive Array

• A different approach uses an adaptive array detector design, which comprises detector rows with different sizes in the longitudinal direction.

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• Variable or non-uniform detectors are composed of elements that are not uniform in size but can be combined with a post-patient collimator unit to generate sections with several different thickness values.

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• Several manufacturers used this approach for their early designs, not used in later generation MDCT.

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Hybrid Array

• This detector design has a number of narrow detector elements in the centre of the detector & a different number of wider detectors (usually double the width of the narrow detectors) on both sides of the span of narrow detectors.

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• The number of narrow and wider detectors can vary.

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Arrangement of detector

24mm Super wide body （16 DAS system）

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24mm Super wide body （16 DAS system）

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• 24 non equidistant detector design, the middle 16 rows 0.75mm，ensure both the image resolution and the isotropic accuracy

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Arrangement of detector

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ADVANCEMENT IN CT TUBE

• Straton tube

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• Maximus rotalix Ceramic (MRC) tube

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• LIMAX(Liquid Metal Anode Xray tube)

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• Vectron X-ray tube

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STRATON X-RAY TUBE

• One of the more interesting developments is the Siemens Straton x-ray tube
• The tube itself is a radical new design, where the entire tube body rotate(RET), rather than just the anode, as is the case with conventional designs.
• This change allows all the bearings to be located outside the evacuated tube & enables the anode to be cooled more efficiently.

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FLYING FOCAL SPOT:

• The no. of measurements channel can be doubled by rapid deflection of X-ray tube focal spot for each projection increasing the image resolution.
• This technology is achieved by electromagnetically deflecting the electron beam within the X-ray Tube.
• For each focus position 2 – measured interlaced projection result, since the detector continue to move continuously which double the sampling frequency & enhance the spatial resolution.

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Straton tube

• The Straton has a low inherent heat capacity of 0.8 MHU, but an extremely fast cooling rate of 5 MHU / min.

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• This compares with typical figures of 7-8 MHU & up to 1.4 MHU / min for existing tubes.

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• The heat capacity & cooling rate combine to produce a tube which Siemens claim as tube with ‘0 MHU', implying that tube cooling considerations are a thing of the past..

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MAXIMUS ROTALIX CERAMIC (MRC) TUBE

• In 1989 Phillips became the 1^st company to introduce MRC

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• Based on the technology of spiral groove bearing , using liquid metal alloy as lubricant.

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MAXIMUS ROTALIX CERAMIC (MRC) TUBE

• Dissipation of the heat via the liquid metal lubricant gave the tube higher cooling capacity.
• Noiselessly rotating anode and had a very long lifetime.
• Avoid waiting time during and between examination.
• Continuous rotation overcame the time to speed barrier
• 200 mm graphite backed anode

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MRC Tube

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MRC Tube

• Anode heat storage capacity - 8 MHU
• Tube voltage 90 to 140 kv
• Tube current 20 to 500 mA
• Anode angle – 7^o
• Directly cooled anode

^USES

• ^{-Cardiovascular imaging}
• ^{-Multi-slice CT}

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LIMAX(Liquid Metal Anode Xray tube)

• In these tubes a liquid metal jet is subjected to fast electrons.
• Liquid metal, eutectics of SnPb, GaInSn, or PbBiInSn, turbulently streaming through a tube close to the cathode, is heated at the focal spot.
• While the heated material is transported through the tubing, cold metal enters the focal spot area.
• Liquid metal is cooled effectively by circulation through a H E
• This is separated from the vacuum by a diamond, W or Mb window of several microns in thickness as compared to stationary anode X-ray tubes, the LIMAX design has shown a sig. improvement in its ability to be continuously loaded.
• However, in the current state of development, the peak power does not reach values in the order of 150 kV, that are required for the latest CT generation.

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LIMAX

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Fig A. Basic principle of the liquid metal X-ray tube. B. The anode module consists of a constricted fluid channel incorporating an exchangeable electron-beam window module. C The anode module itself is connected to a fluid circuit containing a displacement pump and a water-cooled cross-flow heat exchanger. D Infrared imaging of the focal spot temperature.

���������������Vectron x-ray tube���������������

• Stellar detector with UFC detector and with anti-scatter 3D collimator grid integrated into one
• Temporal resolution up to 66ms
• Rotation time: 0.25s
• Spatial resolution 0.22 lp/cm(equivalent to 24mm)
• Max scan speed - 737mm/s
• Voltage : 70-150kV
• Focal spot: 0.4x 0.5 mm

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GANTRY ROTATION TIME

• Is time interval needed for a complete 360° rotation of the tube-detector system around the patient.
• It affects the spiral scan length & thus the coverage of the scan range during a certain period of time. Ultra modern CT systems require only 0.27 seconds for one rotation. A short rotation time has the following advantages: -
• A longer spiral scan can be acquired in the same scan time
• The same volume & slice thickness can be scanned in less time
• Motion artifacts are eliminated
• Savings on contrast media
• Reduced patient Discomfort & Anxiety

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Gantry rotation

• Sub second gantry rotation

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• In 16 slices - 0.5 sec

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• In 64 slices – 0.3 sec

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• In 256/320/640 slices – 0.27 sec.

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• In DS scanners slice- 0.25sec

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Dynamic collimator

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• During helical scanning, some overscanning in the longitudinal direction (z-overscan) is required to ensure that sufficient data are available for reconstruction.
• Dynamic or adaptive collimation is a hardware-based solution for collimating the X-ray beam such that extraneous radiation exposure is blocked by retractable collimator blades.
• Dynamic collimation has the greatest effect in reducing dose for shorter scan lengths and higher pitch values .

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Dynamic collimator

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Figure 1: Examples of (a) conventional and

(b) adaptive section collimation CT scanning protocols. For

adaptive section collimation, shape of x-ray cone beam at beginning and end of spiral acquisition is controlled

by two collimators made of absorbent material

DECT

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• DECT utilizes the principle that different material show different attenuation at varying energy level and this difference in the attenuation can be used for tissue characterization.

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Historical Perspective

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• In the early days, Sir Hounsfield proposed that ,two pictures taken of the same slice at 100KV and at 140 kv has shown that iodine (z=53) can be readily differentiated from calcium(z=20)
• Alvarez , Macovski and Calender also described the theoretical basis of the dual energy scanning in the early 1980s.

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• First commercially available dual energy CT came into use in 2006(Somatom Definition,DSDE)

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Historical Perspective

• Over the time newer modifications and advancement came in dual energy CT scanner

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• In the 2nd gen. of DSDECT , FOV was increased from 26cm to 33cm and the addition of selective photon shield lead to increase in contrast to noise ratio and better and accurate material characterization.

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• Later single source and single detector(SSDECT)was developed (GE healthcare and spectral Imaging)

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Historical Perspective

• With dual-energy CT, two image datasets are acquired in the same anatomic location with two different x-ray spectra to allow the analysis of energy-dependent changes in the attenuation of different materials.
• Each type of material demonstrates a relatively specific change in attenuation between images obtained with a high-energy spectrum and those obtained with a low-energy spectrum, and this attenuation difference allows a more distinct characterization of the features depicted.
• Two different materials that show similar attenuation on images acquired with one of the two energy spectra are often more easily differentiated on images acquired with the other spectrum because of substantial differences in their attenuation

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DECT

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Graph of mass-attenuation coefficients for iodine (blue), calcium (green), and water (red) on CT images obtained at two different energies (vertical dashed lines) shows that these materials can be characterized by comparing their attenuation at the lower energy with that at the higher energy. When dual-energy images reconstructed for 50 and 80 keV are compared, iodine demonstrates a greater decrease in attenuation than calcium does at the higher energy, whereas the attenuation of water remains more or less constant

DECT

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DECT

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DS-DECT

• It was the first commercially available and had 2 tubes
• Arranged at 90* to each other in the same gantry but operating at different kVp.

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• Mean kVp of higher & lower energy tubes were120-140kVp and 80-100kVp resp.

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• The tube with larger kVp had a larger detector of FOV (50 cm) and the lower kvp tube has smaller FOV detector(26cm)

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SS-DECT

• SSDECT scanner uses a single x-ray tube
• Generates high and low energy spectra by rapid changing of the kvp setting (at an interval of 0.5ms)in the same rotation.
• Since the tube current can not be changed so rapidly in order to maximize the contrast to noise ratio, the exposure time ratio is changed between two acquisitions.

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DUAL ENERGY CT:

Dual layered detector

1. Dual layered detector;
1. The detector is formed by two scintillating layer with the top layer attenuating lesser than the bottom layer.
2. The x ray photons with lower energy will likely be absorbed by the top layer and photons with higher energies will pass through it.
3. The bottom layer will interact mostly with the higher energy photons

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Applications of DECT

• Applications in Abdomen :
• Renal calculi characterization
• Renal cyst, renal mass characterization
• Pancreatic neoplasm n necrosis.
• Application in pulmonary
• Pulmonary thromboembolism
• Pulmonary nodule evaluation
• Application in musculoskeletal : application in gout, metal artifact reduction,
• Applications in cardiovascular imaging: myocardial infarction analysis

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Flat Panel Volume CT

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• It is the unique CT design, that is capable of high spatial resolution volumetric and dynamic imaging.
• In the simple term, FPVCT can be thought of as conventional multi-detector CT , in which the rows of detector has been replaced by an area detector.

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• The FPVCT detector has wide z-axis coverage that enables entire organ to be imaged in one axial scan.

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• Furthermore, the scanner provides ultra high spatial resolution in x , y and z-axis(200µm or less)

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Flat Panel Volume CT

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• It consists of area detector composed of a matrix of as many as 2048X1936 elements,
• The scanner has z-axis coverage of 18 cm.
• MAJOR COMPONENTS:

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1. X-ray tube: modified x –ray tube as compare to MDCT

- wide anode angle ( 16º)

- source to detector and source to isocenter distance are 93 cm and 57 cm.

- small focal spot: (0.57 mm)minimal penumbra effect (preserve sufficient photon flux)

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Flat Panel Volume CT

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Applications:

1. The potential application of FPVCT are broad with numerous possibilities in the area of clinical , preclinical , animal and human imaging.

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• The ultra high spatial resolution of flat panel volume CT is ideal for imaging and analyzing skeletal structure; such as trabecular bone and bone maxillofacial structure on microscopic level

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• It can depict dynamic process such as coronary blood flow, myocardial angiographic abnormalities in stroke and perfusion abnormalities in kidney

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• Small animal imaging, tissue engineering experiments.

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Cardiac Imaging

• To reduce the impact of cardiac motion in cardiac imaging , the data acquisition typical relies on ECG signal to indicate the phase of the heart.

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• A cardiac cycle has two phases in which the heart motion is relatively less(end systolic n end-diastolic)
• During end systolic and end diastolic heart undergoes quiescent period of cardiac motion.

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• On the ECG trace , the mid-diastolic phase generally corresponding to a region of 70-75% of R-R interval and the end diastolic phase is 30-35% R-R interval.

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Cardiac Imaging

The basic modes of MDCT data acquisition are

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• Prospective ECG gating and

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• Retrospective ECG gating

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• Prospective Triggered Helical Acquisition

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Advantages

• High spatial resolution
• Real time fluoroscopy
• Volume coverage in one rotation
• Dynamic imaging
• Lexible c- arm like orientatio

Disadvatages

• Low contrast resolution
• Slower scintillation
• Longer scan time
• Lower dynamic range
• Lower SNR in very thin section

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Cardiac Imaging

• The primary challenge required to image a rapidly beating heart is that the imaging modality should provide high temporal resolution.
• It is necessary to freeze the heart motion in order to image coronary arteries located close to heart muscles, since these muscles show rapid movement during the cardiac cycle.
• the imaging modality should provide high spatial resolution to resolve very fine structures such as proximal coronary segments that run in all directions around the heart.

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Prospective ECG triggering

• Step and shoot technique
• The patient’s cardiac functions are monitored through ECG signals continuously
• Temporal resolution with this type of acquisition can range from 200 to 250 msec

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Retrospective ECG gating

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Data reconstruction

• Single cycle data acquisition(Half scan algorithm)

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• Multiple cycle data acquisition( Multi-segment algorithm)

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Data reconstruction

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FPD PORTABLE C & O-ARM CT:�

• C-arm–based flat-panel volume CT is a system in which a cone-beam x-ray tube and a flat-panel detector are integrated with a C-arm gantry .
• The key advantage of C-arm–based flat-panel volume CT is its accessibility.
• C-arm systems offer greater flexibility in orienting the detector around the patient than closed CT gantries do.
• In addition, they have an advanced fluoroscopic capability.
• They are particularly suitable for interventional and intraoperative applications.
• Such systems typically allow image acquisition and rotation around an isocenter to occur simultaneously, making 3D reconstruction imaging possible.

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FPD PORTABLE C & O-ARM CT:�

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FPD PORTABLE C & O-ARM CT:�

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Photographs of a flat-panel-detector–based O-arm flat-panel volume CT system in the C-arm (left) & O-arm (right) configurations. The O-arm configuration is achieved by a telescoping mechanism in the C-arm that provides a closed gantry to allow continuous rotation of the imaging chain. (Image courtesy of Medtronics, Minneapolis, Minn.)

MAMMO CT:�

• A prototype breast CT scanner was designed, fabricated and is currently undergoing clinical testing.
• The CT system operates at 80 kVp, and between 3 and 10 mA. With the 0.3mm of added filtration, the 80 kVp beam has a half value layer of 5.29mm Al.
• The flat panel detector system has an intrinsic pixel size of 0.194mm
• In an effort to reduce scan time even further, the electronics of the detector were modified to achieve 55 frame per second acquisition.

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MAMMO CT:�

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Mammo CT

• These scanners offer 3-dimensional images of the breast in contrast to the 2D images obtained with mammography.
• This procedure is more comfortable than regular mammography, which involves breast compression which is painful for many women.
• However these scanners is less efficient than regular mammography at detecting the microcalcification that can sometimes signal breast cancer.

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CT FLUOROSCOPY:�

• CT scanners commonly have the facility for ‘Fluoroscopy’ i.e. A display of a CT – Image in real time.
• It is achieved through continuous rotation of the gantry without table movement.
• Using fast reconstruction techniques, generally from 1800 linear interpolation data sets, frame rates of 5 frames/Sec. or greater may be achieved.
• Application: -
• Most commonly, such techniques are used in: -
• ‘Biopsy Needle Placement’ for Tissue Biopsy.
• Drainage of Fluid – Filled Lesions.
• Ethanol & RF Ablation of Tumours.
• Placement of Catheters & Guidance of Sacroiliac Injections.

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NISHA KARNA

Disadvantages: -

• It should be noted, however, that although the effective dose may be less than for a standard diagnostic scan, there is the potential for relatively high patient & operator skin dose because scanning is confined to a narrow region of the body.

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Fusion Modality/PET CT/ SPECT

• The modality fusion technology makes less time-consuming, less expensive, and logistically beneficial for patients and staff.
• Can perform measurement within the same system without moving patient relative to table make reregistration easier and help for correlation and attenuation correction.
• Combining both we can achieve physiological information within the anatomical region.

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Micro-CT

• Commonly known as Industrial CT Scanning
• The term micro is used to indicate that the pixel sizes of the cross-sections are in the micrometer range.
• The machine is much smaller in design compared to the human version and is used to model smaller objects.
• There are two types of scanner setups-
• one setup, the X-ray source and detector are typically stationary during the scan while the sample/animal rotates.
• second setup, much more like a clinical CT scanner, is gantry based where the animal/specimen is stationary in space while the X-ray tube and detector rotate around.

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Micro-CT

• Open X-ray system-In an open system, X-rays may escape or leak out, thus the operator must stay behind a shield, have special protective clothing, or operate the scanner from a distance or a different room.
• Closed X-ray system -In a closed system, X-ray shielding is put around the scanner so the operator can put the scanner on a desk or special table.
• Use-
• Both in vitro and in vivo small animal imaging
• Human skin samples
• Bone samples, ranging in size from rodents to human biopsies
• Insects, used to study diverse materials including bone, teeth, medical implants, snow, textiles, concrete and precious stones.
• detecting defects in a diamond and finding the best way to cut it.

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Dose modulation in CT

Tube current modulation

• Basic idea:
• Adapts tube current to attenuation of body region
• Increase tube current for more attenuating area
• Decrease tube current for less attenuating area
• Overall goal: reduce dose yet maintain image quality

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Tube current modulation �

Several flavors

• Angular modulation (in plane)
• Longitudinal modulation(z axis)
• Combination (x, y and z)

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Longitudinal modulation

• Adapts to pt variations from one anatomic region to another along the length of the pt.

-Neck to chest to abdomen to pelvis

• Seeks to produce approximately equivalent image along the length of the pt
• Operator has to select desired image quality parameter:
• Reference image index( GE)
• Reference image acquisition (Phillips)
• Quality reference mAs( siemens)
• Reference std deviation (Toshiba)

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Combination (x, y and z)

• Adapts to pts size
• Adapts to variation from one anatomic region to another along the length of pt and in plane
• Low frequency changes across anatomic regions(z)
• High frequency changes across angular variations(x,y)

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Dose modulation techniques

• SURE DOSE - Toshiba
• DOSE RIGHT- Philips
• CARE KV AND CARE DOSE - Siemens
• AUTO mA OR SMART mA -GE

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Iterative reconstruction dose reduction

• AIDR-3D- Toshiba (adaptive iterative dose reduction)
• ASIR- GE (adaptive statistical iterative reconstruction)
• iDOSE IMR –Philips (iterative model reconstruction)
• ADMIRE- Siemens (advanced modeled iterative reconstruction)

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Metal artifact reduction techniques

• iMAR –Siemens
• MAR-GE
• SEMAR- Toshiba
• O-MAR- pHILIPS

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Metal artifact reduction

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Photon counting detector

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• Photon counting detectors capable of discriminating X-ray photon energies have been developed in past decades for various applications in medical imaging and material science
• Compared to energy-integrating X-ray detectors working in a current mode, photon counting detectors are operated in a pulse mode based on single event, meaning that theoretically each interaction occurred within the detection material can be processed and registered individually

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Photon counting detector�

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• Three types of photon counting detectors have been developed based on the ionization radiation in gases, scintillators, and semiconductors

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Photon counting detector

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Diagrams show detector types. A, In conventional energy-integrating detector, an incident x-ray photon is converted into a shower of visible light photons in a scintillator. Visible light hits an underlying light sensor, where it generates positive and negative electrical charges. B, In photon-counting detector, the x-ray photon is absorbed in a semiconductor material, where it generates positive and negative charges. Under the influence of a strong electric field, the positive and negative charges are pulled in opposite directions, generating an electrical signal

Photon counting detector

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Photon counting detector

• Photon-counting CT is a promising technique, with the potential to dramatically alter the clinical use of CT in the upcoming decades.
• New energy-resolving detectors enable detection of individual x-ray photons and measurement of their energy.
• Relative to conventional energy-integrating detector CT, photon counting CT allows for radiation dose reduction, increased spatial resolution, correction of beam-hardening artifacts,
• And use of alternative contrast agents while creating opportunities for quantitative imaging.

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Disadvantages

• Cross talk
• Pulse pile up

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Photon counting detector

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Photon counting detector

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Figure : A EID B PCD a. shows left upper rib appears eroded b: more uniform appereance with

low noise and left upper rib is nicely seen

Integration of AI algorithms into CT systems�

• Machine learning has created great potential to advance medical imaging, specifically CT scanning, through reducing exposure to radiation and by harnessing the power of Artificial Intelligence.
• The integration of Artificial Intelligence algorithms into CT systems will enable radiologists to provide better images to clinicians, who will in turn provide better treatments based on more accurate diagnosis

NISHA KARNA

SUMMARY

• The advances in MDCT scanners have presented new opportunities for improved patient imaging and throughput.
• However, these scanners bring with them new concepts that have to be understood and new tradeoffs that have to be made.

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• The advancements includes different multiple-row detector designs, cardiac imaging principles with MDCT, pitch and its influence on radiation dose, image quality and section thickness.

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NISHA KARNA

REFERENCES

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• Computed Tomography Principles, Design, Artifact Recent Advances by Jiang Hsieh
• Diagnostic Radiology Recent advances and applied physics by Arun kumar, Veena Chaudhary, Niranjan Khandelwal
• Christensens Physics of Diagnostic Radiology Fourth edition by Thomas S.curry, James Dowery
• Computed Tomography in the 21st Century: Current Status & Future Prospects , Nitin P. Ghonge, JIMSA JAN-MARCH 2013 VOL 2
• Past presentations and various web sites of manufacturers

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NISHA KARNA

Thank you

NISHA KARNA