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Published on : May 11, 2019 | Views : 2550 | Downloads : 8

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Slide 1-

The Future of CT Matthew Russell CT Section Manager Sydney Adventist Hospital
Slide 2-

Siemen’s Somatom World Summit Conference held biannually Held in Singapore in June 400 Radiologists around the world, a 6 Aussie radiographers and the token Kiwi were invited
Slide 3-

Siemen’s World Summit Efficient Workflows Scan Techniques Advanced Software Next Evolution of CT Technology
Slide 4-

Efficient Workflows SOMATON go.Now
Slide 5-

SOMATON go.Now Mobile tablet Camera New Workflow Design Remote Control
Slide 6-

Mobile Tablet Patient Details Protocol Topogram Start Button
Slide 7-

go. Technology Assesses coverage Assesses contrast Automated recons
Slide 8-

Scan Techniques CT Myocardial Perfusion
Slide 9-

CTCA vs CT Myocardial Perfusion CTCA Morphological assessment of the heart Identification and classification of CAD Assessment of the degree of stenosis CT Myocardial Perfusion Functional assessment of the heart Identification of myocardial ischemia Assesses the hemodynamic significance of coronary artery stenosis
Slide 10-

What is CT Myocardial Perfusion CTCA Calcium Score CT Coronary Angiogram CT Myocardial Perfusion CT Myocardial Perfusion(Rest) CT Myocardial Perfusion(Stress induced) Stress agents primarily used are adenosine and regadenoson CT Delayed Enhancement
Slide 11-

Different approaches to CT Myocardial Perfusion Static Single Energy Perfusion Encompasses entire left ventricle Single shot acquisition Best performed on scanners with large detectors Always acquired during CTCA so no additional radiation required Qualitative assessment performed by visualisation of the left ventricular myocardial enhancement Limitations: Acquisition timing Segmental scanning causing difference in uptake timing
Slide 12-

Different approaches to CT Myocardial Perfusion Static Dual Energy Perfusion Performed on dual source scanners but can also be performed on scanners with fast kVp switching technology Iodine distribution map created from merging 2 data sets of different energy spectra Myocardial blood pool is quantified from the amount of iodine per voxel Superior diagnostic performance when compared to single energy CT myocardial perfusion Limitations: Acquisition timing and segmental scanning Loss of temporal resolution Non-standardised evaluation of the iodine maps
Slide 13-

Different approaches to CT Myocardial Perfusion Dynamic Dual Energy Perfusion Two approaches 256/320 slice scanner Second/Third Generation Dual Source using shuttle mode Only way that CT can directly measure myocardial perfusion Samples the myocardial attenuation multiple times during the first contrast uptake Limitations: No morphological assessment of coronary arteries Extended breath hold (~30s) Spatial misalignment from table movements Higher radiation dose and furthermore if CTCA still required Time consuming (exam time ~ 45min)
Slide 14-

Dynamic CT Myocardial Perfusion Moderate – severe mixed calcified/atheroma stenosis noted in the LAD Minimal atheroma stenosis noted in the RCA Severe atheroma stenosis noted in the LMB or OM Medial wall of the myocardium affected by LAD Lateral wall of the myocardium affected by the LMB Superior aspect of the myocardium could be a result of both LAD and LMB TAC curve identifies the hemodynamic significance of the lesions
Slide 15-

Why do we need CT Myocardial Perfusion Multiple modalities used to assess myocardial ischemia Cardiac MRI SPECT MPI Invasive Coronary Angiography
Slide 16-

Comparison between modalities
Slide 17-

Advanced Software CT Fractional Flow Reserve (FFR) Cinematic Volume Rendering Technique
Slide 18-

What is FFR? Fractional Flow Reserve is a technique used in Invasive Coronary Angiograms to assess the hemodynamic significance of a lesion FFR is measured by using a pressure wire to calculate the ratio between coronary pressure distal to the stenosis and aortic pressure under maximal myocardial hyperaemia If the ratio falls under 0.75 – 0.8 there is association with myocardial ischemia Cardiologist will visualise the stenosis. If the stenosis is believed to be 70% or greater the FFR may be measured to help make a clinical decision whether revascularisation is required. Intervention may include angioplasty, stenting or coronary artery bypass/graft
Slide 19-

Where does CT fit into this? CTCA is becoming a widely accepted examination to assess CAD The examination takes approx. 20 minutes Minimally invasive with only the need of a cannula to be inserted Small volume of contrast (~60 – 80mL) Low radiation dose ( avg. 2 – 3 mSv on our Force) Patient only need to hold breath ~ 10s
Slide 20-

CT FFR CT FFR was a concept that believed the information achieved from FFR performed in Invasive Coronary Angiogram could be achieved in a CT Scan Furthermore, this could be achieved by doing no more than a standard CTCA The software could utilise the anatomical data obtained from the CTCA dataset in conjunction with computational fluid dynamics to calculate the FFR In 2014 an American company HeartFlow received FDA approval for the use of this software
Slide 21-

CT FFR Technology Three main elements: Anatomical modelling of coronary arteries Physiological modelling of blood flow Solution on equations of blood flow on a computer
Slide 22-

HeartFlow First company to provide an external service where referrers could upload the CTCA datasets Data would be loaded into a supercomputer for the analysis Utilises a 3-dimensional CT-FFR modelling technique that solves ‘millions of complex equations’ to assess the blockage Calculation time ~ 2 - 4 hours Comes at a hefty price of US $1500 As good as this sounds is this clinically viable????
Slide 23-

HeartFlow Technology 3D modelling: Anatomical modelling and left ventricular mass extracted from CTCA data Bloodflow is coronary arteries is calculated since blood flow at rest is proportional to myocardial mass Left ventricular mass is measured from volumetric imaging of the heart Segmentation of the coronary arteries Resting bloodflow is computed from left ventricular myocardial mass, accounting for the size and number of branches 3D model details the lumen boundaries, captures 3 components of velocity vectors. Accounts for pressure gradients across the stenosis Limitations: Completely reliant upon image and scan quality
Slide 24-

HeartFlow Examples
Slide 25-

Siemens cFFR March 2017, Siemens and HeartFlow are colloboratively working towards a 1 Dimensional computational analysis technique 1D Modelling requires less computational power since there is one component of velocity vector and the software makes assumptions about bloodflow through the arteries This product will be available on Syngo VIA workstations and hopefully provide a faster alternative for clinical sites Product has been developed but still not commercially available yet. Maybe Seb can tell us more when he gets back from RSNA
Slide 26-

Cinematic Volume Rendering Technique The new version of imaging that we currently output known as VR images. This technology was inspired by CGI used in movies Provides a 3D photo-realistic image of the human body using either CT or MRI data Uses a image technique known as shading Requires considerable more computational power than standard VR imaging
Slide 27-

Cinematic Volume Rendering
Slide 28-

Evolution of CT Technology Photon Counting Detectors
Slide 29-

The Evolution of the CT Detector 1st Generation: Xenon gas detector to convert x-rays to electric current 2nd Generation: solid state detector was introduced that was more efficient by converting the x-ray into light then converting the light into electric current and an ADC to digitise the signal 3rd Generation Scintillator detector introduced into the Force where there conversion of light to current and digitised is combined 4th Generation Photon Counting is able to directly convert x-rays to electric current
Slide 30-

Scintillator Detector Technology X-ray photon hits the detector and the scintillator layer converts the photon into light Light then hits the photodiodes and converted into an electric current Scintillation layer is made of ceramic material with septa or divisions separating the detector into pixels This is to prevent signals being received on the wrong photodiode
Slide 31-

Photon Counting Technology X-ray photon hits the detector passing through the Cadmium Telluride layer When the photon hits the Cadmium Telluride it is converted into a free charge, which is proportional to the energy of the photon By having a strong electrical current induced through this layer, this free charge can be directed to the pixelated anodes The strong current tries to direct the free charges to the closest anode to prevent loss of information or incorrect information from hitting another anode.
Slide 32-

Benefits of Photon Counting Technology 100% geometric efficiency - scintillator detectors run at appox 70% efficiency. Photon counting technology will be able to improve on that substantially and decrease radiation dose by an estimated additional 30% No electrical noise – caused by the conversion of the photon to light then light to electrical current Higher spatial resolution – currently 0.4mm on the Force but 0.2mm could be achievable Spectral separation – every scan will have the dual energy capabilities
Slide 33-

Spectral Separation All elements have different k-edges and spectral curves By using selective binning or grouping we can categorise and assign the elements This is normally performed with the aid of Dual Energy, but with the spectral separation that can be achieved with photon counting every scan will be ‘Dual Energy’
Slide 34-

Current Problems A) Charge Sharing – a photon interacts with the detector and the energy is split B) K-Escape – a photon reacts with the detector and the energy can be split with part of the energy being pushed to another detector pixel C) Consecutive photons hitting the detector with too short of an interval D) Compton Scatter Solution: Larger and slower Photon Counter Detector (PCD)
Slide 35-

Current Problems Pulse Pile Up Solutions: Smaller and faster PCD
Slide 36-

The Gang