The Fundamentals of MSCT Cardiac Imaging Using Dual Source Technology

Welcome to the eLearning The Fundamentals of MSCT Cardiac Imaging Using Dual Source Technology Hardware & Software   Cardiac workflow Patient preparation Cardiac protocols Image reconstruction Clinical Practice Disclaimer All information in this presentation is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any healthcare practitioner reading this information is reminded that they must use their learning, training, and expertise in dealing with their individual patients. This material does not substitute for that duty and is not intended by Siemens Medical Solutions to be used for any purpose in that regard.   This length of time required to complete this course will vary depending on, but not limited to, expertise of subject matter, reading speed, interruptions, and internet connection speed.  The accrediting agency is responsible for determining the number of CE credits awarded for this course.   This activity may be available in multiple formats such as web-based training and an actual live event. The ARRT does not allow CE activities such as internet courses, live event, home study programs or directed readings to be repeated for CE credit in the same or any subsequent biennium.   Any of the protocol(s) presented herein are for informational purposes and are not meant to substitute for any clinical judgement in how best to use any medical devices. It is the clinician that makes all diagnostic determinations based upon educational, learning and experience. Fundamentals of cardiac CT scanner evolvement, past to present Fundamentals of modern CT scanners including gantry components and basic requirements of a CT scanner to provide good cardiac image quality Fundamentals of cardiac CT including ECG, cardiac cycle, two main cardiac acquisition modes Fundamentals of cardiac image reconstruction – Physics-simplified version Cardiac CT dose considerations Fundamentals of cardiac CT examination including patient preparation, positioning and scan range, protocol choice and contrast injection, and image reconstruction plus how to deal with arrhythmias Sir Godfrey Hounsfield (8/28/1919 – 8/12/2004)   1971 1st Clinical CT Scanner 1972 1st patient 1973 commercially available   Source: http://nobelprize.org/nobel_prizes/medicine/laureates/1979/hounsfield-autobio.html Hounsfield Unit Definition Indication Substance densities in Hounsfield Units X-Ray attenuation unit used in CT Scan interpretation Computed Tomographic Scanning (CT Scan)  Air: -1000, Fat: -50 , Water: 0 Characterizes the relative density of a substance   Soft tissue such as muscle: +40 Each pixel is assigned a value between -1k to 1k   Calculus: +100 to +400     Bone: +1000 Early scanners… The device uses X-rays to scan from different angles and a computer to assemble the images into a cross-section Rotation time several seconds, reconstruction time up to 10 minutes/image. 14 x-ray tubes  1/60 s temporal resolution  Up to 240 slices in 1/60 of a second  Dimensions: 15 ft. in diameter, 20.5 ft. in length  Weight ~ 17 U.S. tons  Not commercially available   A powerful electron beam is generated and then focused onto one of four tungsten target rings positioned beneath the patient. Each 210 degree sweep of the electron beam produces a continuous 30 degree fan beam of x-rays that pass through the patient to a stationary array of detectors which generates cross-sectional images (33, 50 and 100 ms temporal resolution). Limitations of EBT: SL (1.5/3.0mm) Image noise Single/dual slice: Long breath hold Couch Detectors Data Acquisition System (DAS) Gun Deflection Coil Target Rings Detector 1 Detector 2 Patient table Gantry X-ray unit 2 Rotation of X-ray unit and detector High Temporal-Resolution Minimize motion artifacts Fast Gantry Rotation   High Spatial Resolution-Depict coronary anatomy (~4 mm to 1 mm of diameter and smaller) Thin Collimation   Fast Continuous Coverage -Whole heart in one short breath-hold Multi-slice CT   Synchronization to Heart Beat-Consistent cardiac phase ECG Gating   SLR Camera: Temporal resolution = shutter open time or shutter speed Shutter speed determines image quality of objects in motion Slow Shutter Speed = Blurred Motion Image  Fast Shutter Speed = Clear Still Image   The Swan Series Credit: Image courtesy of Mr. David Hofmann ® His ONLINE Portfolio has an excellent series of wildlife pictures where this image was extracted from one of his photo album. Image copyright © 2005.   LAD  22.4 mm/s ± 4.0 CX  48.4 mm/s ± 15 RCA   69.5 mm/s ± 22.5   Double Z-Sampling Learn more about the Double Z-Sampling   Siemens Ultra-Fast Ceramic Detector Learn more about the Siemens Ultra-Fast Ceramic Detector Element HTML Sound File Audio ScriptSiemens Ultra-Fast Ceramic detector technology enables the simultaneous readout of two projections for each detector element. The ultra-high speed detector electronics enables the readout of two by 64 slices for every viewing angle allows for full 128-slice acquisition. Compared to conventional CT acquisition technology, each measurement requires half the time and half the dose. Stellar Detector Learn more about the Stellar Detector Technology   1.4mm 1.0mm 0.7mm 0.3mm Sub second breath hold using the Flash Mode   3-4 second breath hold Adaptive Sequence Mode   4-7 second breath hold Spiral Mode Suggested Lead Placement 128 x 0.6mm slice heart scan Integrated Cardiac Evaluation tools 0.28s 0.33s gantry rotation 75ms / 82ms standard temp. resolution (dual source, using one-segment recon.) 37.5 / 40.5 ms with two-segment recon The heart contracts when pumping blood and rests when receiving blood. This activity and lack of activity from a cardiac cycle can be illustrated by an Electrocardiogram (ECG). Atrial contraction Diastolic phase Ventricular contraction Systolic phase Ventricular Relaxation P R Q S T U P: contraction of the atria Q,R,S: contraction of ventricles T: recovery of the ventricles Chambers undergo alternating periods of relaxation and contraction   Relaxation period - DIASTOLE   Contraction period - SYSTOLE Systolic Phase Diastolic Phase Systolic Phase R-R Interval 1000 ms 1200 ms 700 ms 600 ms 600 ms 600 ms Positive ms Negative ms -400 ms -400 ms -400 ms Phase Start 100% 100% 100% 60% 60% 60% Prospective Triggering   Retrospective Gating SEQUENTIAL Scans Estimated arrival of the next R-wave 75 ms temporal resolution Dual-Source Definition Flash CT 82 ms temporal resolution Dual-Source Definition CT Single or multiple predefined cardiac phases depending on system being used ECG recording during spiral acquisition with retrospective image reconstruction True match of the data to the ECG trace 75/82 ms temporal resolution Data possible for the entire cardiac cycle   Data are collected for the entire volume and can be freely reconstructed to represent any point in the cardiac cycle Subsequent reconstruction can be performed to reposition the data and create a new set of images   "Imagination is more important than knowledge." Physics-simplified version To reconstruct an image, we need only data from half of the scan rotation Multi-segment reconstruction   Single-segment reconstruction Possible at all heart rates with Dual Source scanners Requires data from several different heart beats to be combined to create the image Computer assisted selections Best Diastolic/Systolic Phase Two X-ray sources and two detectors Heart rate independent temporal resolution of 75 / 82 ms Single-source CT 165ms 165ms 60 bpm 100 bpm   Heart rate independent temporal resolution of 75 / 82 ms Definition Flash and Dual-source Systems Learn more about the Definition Flash and Dual-source Systems. Element HTML60 bpm100 bpm75 ms 82 ms75 ms 82 ms Sound File Audio ScriptThis allows us to achieve good image quality at low heart rates and also at higher or irregular heart rates, free of motion artifacts. Unlike a single-source CT system, which has “sweet spots” for single-segment reconstruction, the Definition Flash and Dual-source (DS) systems are able to use single-segment (75/82 milliseconds) reconstructions at any heart rate. With this, true temporal resolution can be consistently achieved, independent of the patient’s heart rates, without the drawbacks of multi-segment reconstruction or beta blockers. Nominal output during diastole and no output in systole by adjusting the width of the maximum dose window used during ECG dose modulation.   Apart from the general factors such as gender and irradiated organs, the effective dose for cardiac imaging is also dependent on: Scan modes: Flash Spiral Cardio modes* provide the lowest dose (< 1 mSv with 100 kV) Width of the maximum dose window used during ECG dose modulation ECG gating techniques: retrospective gating technique utilizes higher dose compared to prospective triggered technique Scan parameters such as kV settings; 100 kV protocols provide lower dose Patient heart rates: higher heart rates use higher pitch and less dose for spiral scans (→ Pitch Adaptation)   Pre-medication - Beta Blockers   Oral (Metoprolol) 50 to100 mg @ 30 - 90 min Explanation of procedure Hyperventilation (no longer necessary) Intravenous (Metoprolol) Up to 4 x 5 mg Patient Instructions Observe ECG response during breath hold Nitrates to engorge the coronary vessels in conjunction with beta blockers   Rehearse breath hold   (1) Europe (2) USA Suggested Lead Placement Patient Supine   Range just below the carina to 1cm below the diaphragm   Range: »12-14 cm   Targeted Field of View 150-220 mm   Inspiratory breath hold You will need: 60-80 ml @ 5-6 ml/s 40-50 ml Saline Chaser Method to determine peak enhancement HU Time Early Late Optimal Window Determine the Optimal Scan Delay for: Maximum Uniform Opacification Save Contrast Medium Dosage Avoid  Artifacts (Right heart/SVC) Small compact bolus 20 ml @ 5-6 ml/s   Ascending Aorta Low dose sequential scans, every ~ 2 s   Scan delay (~10 s), time to peak + 5 s additional delay to avoid excessive contrast in the right atrium Injection Protocols 65 – 80 ml @ 5-6 ml/s with Saline chase, 50 ml @ 5-6 ml/s   Monitoring scans: Ascending Aorta Shallow breathing Scan delay: 10 s Cycle time: 2 s Threshold:100-150 HU   Additional trigger delay of about 4-5 s if Automatic Patient Instruction (API) is included   Tracks the arrival of the contrast bolus in real time Tailors the start of the spiral scan to the individual patient Achieves optimal enhancement without the guess works Fast response time (<2 s) reduces contrast usage Principles of Automatic Bolus Tracking Pre-monitoring reference scan Start injection Monitoring scans Spiral scan Which cardiac protocol do I choose? Lowest dose  < 1 mSv with 100 kV Low dose 3-4 mSv with 100 kV Requires fairly consistent heart rate < 85 bpm Fast scan, 3-5 sec Limited R-R adjustments possible after scanning Higher dose and does not require a consistent low heart rate Most flexibility of data use after scanning Scan time 5-9 sec Possible to create multiphase images Preview Series 0% 100% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% RCA-Series 20%, 25%, … 60% LAD-Series 40%, 35%, … 80% RCA: Optimal Time at 40% LAD: Optimal Time at 60% - 400 ms - 500 ms When ectopic beats and sub-optimal ECG traces are presented in the scan data, the ECG Trace Editor can be used to modify the ECG signal and synchronization time points (Syncs). This function is only activated on the Trigger card after acquisition. Disabling ectopic beats (→ Disable Sync) Deleting ectopic beats (→ Delete Sync) Inserting time points (→ Insert Sync) Modifying synchronization time points(→ Shifting Sync) Reverting to the original ECG trace When using Disable Sync, both relative (% RR) and absolute (ms) units may be used to set a time point for image reconstruction. (1) Before Disabled sync (2) After Disabled sync The disabled data bar on the right side of the dots is highlighted in dark blue. When using Delete Sync, absolute time (ms) is recommended for phase selection because this parameter links the scan data exactly to the R-peaks of the remaining heart beats in the ECG trace. (1) Before Disabled sync (2) After Disabled sync The data bar at the extra systolic beat right behind the dot (red circle) is deleted from the trace and the local heart rate (red box) is changed due to the erased heartbeat. When using Insert Sync, absolute time (ms) is recommended for phase selection because this parameter links the data bar more precisely to the newly-inserted R-peaks. (1) (2) (1) Original Sync pulse position (2) New Sync pulse position after shifting If the ECG signal is weak, irregular, or when the heart beats are extremely erratic, the R-peaks may not be correctly synchronized to the scan data. When these incidents occur, the dots (Syncs) are offset to the positions of the R-peaks resulting in misregistration artifacts. This can be easily rectified by left-mouse click on each erroneous dot (circle) and dragging it directly over the R-peak before performing image reconstruction. The local heart rate and the position of the blue reconstruction data bar are changed as a result of shifting the position of the Sync pulse (arrow) as shown in the following screenshots.   Perform reconstruction with original ECG first Scroll through entire trace after editing Always possible to go back to original ECG trace Fundamentals of cardiac CT scanner evolvement Fundamentals of modern CT scanners Fundamentals of cardiac CT Fundamentals of cardiac image reconstruction Cardiac CT dose considerations Fundamentals of the cardiac CT examination Again, thank you for your time! CT applications hotline