Introduction to PET Respiratory Gating

Upon completion of this course you should be able to: • Explain the concept and theory of respiratory gating in PET imaging • Describe the differences between phase based gating vs. amplitude based gating • Describe CT prospective and retrospective gating • Demonstrate the setup and usage of the Anzai Respiratory Gating system • Demonstrate the setup and usage of the Varian RPM and RGSc Respiratory Gating Systems • Describe how to acquire and reconstruct a respiratory gated study   Introduction to PET Respiratory Gating         Respiratory Motion: • Complicates diagnosis of thoracic lesions • Causes errors in definition of target volumes • Causes blurring Leads To: • Over-estimation of lesion volume • Underestimation of SUV Motion Related Blurring Commonly Seen In: • Lung nodules and tumors  • Liver tumors • Pancreatic tumors • Motions can be as large as 3 cm locally • Direction of motion and its magnitude are constantly changing.  Different parts of the anatomy move in different directions at a given time. • Lung tissue moves mainly in the superior-inferior direction • Abdominal tissues in the abdomen can move in different directions • The respiration cycle in most people includes a long semi-quiescent period between breaths • Signal related to patient's breathing • Measurements based on signal's strain gauge belt worn around the patient's chest or abdomen while lying supine on the table • Load cell senses the strain and the response generates a voltage level • Waveform produced • Some breaths were deeper than others (Variable Breath Amplitude Curve) • Relaxed position between breaths do not always give the same signal  (Changing Baseline Curve) • Similar to cardiac gating • Driven by triggers from the respiratory monitoring device • PET scanner did not record the waveform • Phase-based gating froze the inspiration and expiration sides of the cycle • Respiratory gating equipment must be configured and adjusted for each scan • Large amount of data is generated • PET image noise is high because scan is divided into many intervals • Bad triggers due to irregular breathing which get rejected • Some bad triggers do not get rejected • Variable breathing patterns OncoFreeze is an optional feature Static HD•Chest • Selects data from the area of the respiratory curve with least motion • Uses ~ 1/3 of all counts acquired • Additional scan time can be used to compensate for statistics HD•Chest OncoFreeze OncoFreeze • Uses HD•Chest image as a reference • Applies the Optical Flow algorithm to utilize 100% of all counts acquired Images courtesy of Siemens Healthineers Training Center   Static Optical Flow Algorithm HD•Chest   OncoFreeze           OncoFreeze uses the HD•Chest image as a reference and employs an Optical Flow algorithm to deblur the static image until it matches the HD•Chest image, using 100% of the information. Allows for better IQ at routine acquisition time (100% statistics). • Produces a single respiratory gate with a user-specified fraction of PET data (e.g. 35%) >> Optimal gate • PET data in optimal gate was recorded when waveform values were within a certain range • Range is determined by algorithm to include the smallest amount of respiratory motion (U-L minimized) (HD•Chest with eMoCo) Motion Estimation • Divide interval between breaths into several gates • Reconstruct images for each of these gates • Select one of these gates as reference >> End-expiration • Estimate motion between each of the gates and the reference >> 6 respiratory gates = 5 x sets of motion vectors Applying the Correction • Motion correction is applied to reconstructed images • Deform each gated image into the state of the reference gate • Motion corrected image + Sum of the deformed gated images Challenges • Images of all gates have to be reconstructed (e.g. 6x) • Motion has to be estimated for each gate other than reference gate (e.g. 5x) Reconstruction time is > 6x longer than for static images Optical Flow Algorithm follows flow of activity in image • Interpretation of motion as blurring kernel • Mapping of activity in motion-free gated image to motion-blurred static image containing 100% of PET data • Reduced processing time and memory requirements Use a Respiratory Gating protocol for acquisition •  RespiratoryGated •  RespiratoryGatedCBM •  RespiratoryGated_RespMatching •  RespiratoryGated_RespMatchingCBM CBM speed or time per bed for the gated scan regions can be the same setting as the static scan. Recon Subtask Card OncoFreeze is an extension of the iterative reconstruction algorithm and is not available for back projection reconstructions. Replay Subtask Card Gated Static+Gated Trigger Subtask Card Choose Trigger Unit: OncoFreeze (OncoFreeze replaces the previous option Resp In/Ex). Set Duty Cycle: Influences blurring, not image noise. • Sequential, non-spiral • Triggered by a patient's respiration at a set phase • Utilizes Anzai or Varian gating devices • Must be configured to provide a trigger or "X-ray on" signal • Uses spiral acquisition limited to 100 seconds in duration • CT scan is acquired simultaneously with the recording of the respiration waveform • Utilizes Anzai or Varian RPM configured to full respiratory cycle • Allows reconstruction at any phase of respiratory cycle •  Single-phase •  Multi-phase •  Gated • Load Cell technology • Supports both phase and amplitude gating • Used for capturing and storing a signal representing the patient's respiratory cycles Load Cell Fixing Belt • Available in sizes - XS, S, M, L, XL Load Cell or Pressure Sensor • Low Sensitivity (best for deep breathing patients) • High Sensitivity (best for shallow breathing patients) Sensor Port • Receives analog respiratory signal from Respiratory Sensor • Converts it into digital and transfers it to Personal Computer •   Under control of Personal Computer, Sensor Port outputs gating signal to            external equipment Relay Box • Relays the transferred data between Sensor Port and Personal Computer • Connected to the Gate Disable Switch and external equipment Personal Computer • Displays respiratory information from Sensor Port on the monitor  • Commands Sensor Port to output gate signal to the external device Gate Disable Switch  • Equipped with a push-button switch which permits gate signal shut-off when pushed • LED turns blue when pushed  There are two types of respiratory triggering that you can choose from: Waveform Gating or OncoFreeze (optional feature) Anzai & Waveform Respiratory Gating Anzai & Waveform Respiratory Gating Checklist TitleChecklist TypeChecklist Content1.HTML Turn on the HOST COM. switch to the Waveform selection.   2.HTML Turn on the power to the Sensor Port. 3.HTML Put the Load Cell Fixing Belt on the Patient. Put the Load Cell into the pocket of the Fixing Belt. 4.HTML Adjust the fitting of the Load Cell to the patient so the GOOD LED on the Amp. Box turns on. Acquire the study using an OncoFreeze protocol. 5.HTML Use the syngo MI Acquisition Workplace Trigger subtaskcard to make adjustments to the waveform. Trigger Unit = OncoFreeze Duty Cycle = Larger (extends duration of gates and accepts more motion in the images or more blurring) or Smaller (narrows the duration of gates to reject more motion).  100% of the data is used so the Duty Cycle only affects motion in the images. Click the pop-up below to view the steps associated with the Anzai Respiratory Gating system using the Trigger method. Anzai & Trigger Respiratory Gating Anzai & Trigger Respiratory Gating Checklist TitleChecklist TypeChecklist Content1.HTML Turn the HOST COM. switch to Trigger.   Turn on the power to the Sensor Port. 2.HTML The trigger method begins by launching the AZ-733VI application from the desktop of the laptop.   3.HTML Next, register the new patient by clicking the Patient File Management icon on the main screen. Click the New Patient Entry icon on the File Management screen. 4.HTML Enter the patient's name and Patient ID No. then click the Save button. Once the patient is registered or if using an existing patient, select the patient for the examination from the list. Click the New Analysis icon. 5.HTML Put the Load Cell Fixing Belt on the Patient. Put the Load Cell into the pocket of the Fixing Belt. Adjust the fitting of the Load Cell to the patient so the GOOD LED on the Amp. Box illuminates. 6.HTML You can adjust the Respiratory Waveform automatically using software or manually, using the sensor port.  To manually adjust the respiratory waveform, click on the Manual Adjustment icon. Use the Position slider to adjust the baseline of the waveform.  The Magnification slider adjusts the amplitude of the waveform. 7.HTML Click the waveform and it automatically adjusts so the level fits 0-100. 8.HTML To adjust the waveform automatically using the software, click the Automatic Ajustment icon. 9.HTML You can also adjust the respiratory waveform using the Sensor Port. Begin by pressing the CH1 button and then adjust the baseline with the Position dial and the amplitude with the Magnification dial until the level fits 0-100.  10.HTML To automatically adjust the waveforms, press the AUTO button. Once the waveform is automatically adjusted use the manual method to make minor adjustments if needed. 11.HTML Next, you will need to set up the Gate Signal output. Navigate to the Gate Setup area located on the main screen.   Setup the gate signal as the output at the inhalation peak by selecting Peak Mode (a) from the drop down menu shown below.  Select In-Peak (b) as the Start Point and set the Gate Width at 100 ms (c). Lastly, click to activate the Preview (d) check box to preview the gate signal output. 12.HTML The next task is to confirm the parameter settings. Click the Setting Lock icon on the main screen.     For the External Modality field, select (Port0) SIEMENS Diagnostic Imaging.  Confirm the settings in the Safety Function fields. Once complete, click the OK button to confirm the settings. 13.HTML To start the acquisition, click the Start icon on the main screen.  Next, click the Gate Enable icon on the main screen. 14.HTML When the Gate Output screen appears press the Enter key. The gate signal output to the Biograph scanner starts. Proceed with the acquisition on the syngo MI Acquisition Workplace of your scanner. To stop the Anzai Respiratory Gated Acquisition, click the Stop icon on the main screen. Click the Yes button in the End of the Process window to save the respiratory waveform. Adjusting the Gain and Offset of the respiratory waveform:   • Modify Waveform button • Use Gain and Offset sliders to make adjustments • Multiphase Mode - On • Multiphase Mode - Off • Real-time Position Management • Non-invasive • Video based • Clean imaging and treatment of lung, breast, and upper abdominal sites • Supports both phase and amplitude gating Gating Interface Box • Connects the infrared camera to the workstation RPM Workstation • Houses software • Allows monitoring of gate signals   Marker Block • Placed on the patient to follow the patient's breathing • Allows tracking of the motion Infrared Camera • Tracks the Marker Block and records the motion of  the device 1. Open the Trigger subtask card 2. Click the Import button. 3. Locate and click on the .vxp file in the directory 4. Click the Import button. When the acquisition is complete, import the .vxp file from the Trigger subtask card.   Options for File Import: Network Share • When logged in as meduser, create a new directory on your H drive • Partition and share the directory USB • Copy and transport to MI Acquisition Workstation The imported .vxp file will populate the Trigger subtask card. Varian Respiratory Gating Scanners or RGSc equipment includes:  • Workstation Unit • RealTime Unit • Reflector Block • Camera • Workstation Monitor Reflector Block • Placed on the patient to follow the patient's breathing • Allows tracking of the motion Camera • Tracks the reflector block   Options Varian RGSc Cabinet: Workstation Unit • Contains the hardware and software to run the Varian RGSc workstation Real-Time Unit • Stores the data collected by the camera and sends it to the workstation Workstation Monitor • View the software user interface (UI) CT Prospective Gating: • Start after topogram but prior to the CT scan • Select Record and Enable Gating in the Varian software UI • Provides the Trigger (X-ray ON signal) to the CT gantry • Start CT scan and allow to complete • Stop Varian gating • No need to save .vxp file • Trigger subtask card is not present in prospective CT protocol CT Retrospective Gating: • Start after topogram but prior to the CT scan • Select Record in the Varian software UI • Start CT scan and allow to complete • Stop Varian gating and save the .vxp file with a unique name for CT dataset • Start/stop the Varian gating with each subsequent CT scan • Trigger subtask card is present  • Waveform not viewable until imported from Varian system PET Gating: • Start after topogram and CT scan but prior to the PET acquisition • Select Record in the Varian software UI • Start PET acquisition and allow completion • Stop Varian gating and save the .vxp file for import with a unique name for PET dataset • Import the .vxp files • Waveform is displayed in the Trigger subtask card Informs the software that an external unknown gating device will be used for respiratory gating. To activate, select: • Options >> Configuration >> Respiratory Gating >> Open Interface Informs the software that an external unknown gating device will be used for respiratory gating. To activate, select: • Varian RGSc Options >> Configuration >> Respiratory Gating >> Device >> Varian RGSc • Varian RPM Options >> Configuration >> Respiratory Gating >> Device >> Open Interface • Generates time-tagged, continuous count data over predefined intervals • Acquire all count data and replay data using different gating parameters • Types of signals include: •   Respiratory gating devices (Anzai or Varian)  •   Motion from Listmode (Only dual cardiac/respiratory exams on systems with the CardioFreeze option) 1. Register the patient. 2. Define the study. a. RespiratoryGated b. RespiratoryGatedCBM c. RespGated_RespMatching d. RespGated_RespMatching CBM 3. Select Exam. 4. Position the patient. 5. Attach the respiratory gating device. a. Varian RGSc and Anzai - make sure the patient's respiratory curve is available on the Trigger subtask card. 6. Acquire the CT topogram and spiral scans.   a. Anzai:  After the respiratory signal is done, the Trigger subtask card displays in the curve.  b. Continuous pink lines appear to indicate the uninterrupted radiation exposure over several breathing cycles.   c. Retrospective Gated Spiral   – Lung volume is continuously covered – Interface records patient's breathing signals simultaneously for retrospective reconstruction • Gate can be selected on contiguous beds/ranges. All beds/ranges can be static. • Respiratory gating in chest and abdomen • Reduces effects of respiratory motion • Other regions of the body, may not be necessary • Acquisition times on static regions can be shorter To Acquire: • Select respiratory gated protocol • Configure Routine subtask card as follows:   • Turn Physio on for gated beds • Turn Physio off for non-gated beds • Allows manipulation of PET list mode to reconstruct data • Types of Replay include: • Static • Dynamic • Gated • Static+Gated (Biograph mCT and Vision only) Static Replay • Results in a single sinograpm with the same characteristics as a single bed WB scan • Allows use of series in applications that do not support dynamic or gated image sets Dynamic Replay • Frame Definition table • The frames, timing and delays will need to be defined Gated Replay • Must be acquired with a respiratory waveform signal Static+Gated Replay • To use the Static+Gated type, you must first acquire PET data using a Gated Respiratory protocol Dynamic option not avialble for CBM. • Time Window of data used for image reconstruction • Time Window is determined by Rotation Time to complete one revolution of the X-ray tube • Temporal Resolution is improved by using a Half Scan reconstruction method • CT Rotation Time determines the Phase Width for CT reconstruction • Common Rotation Times are 1.0 and 0.5 seconds Example: • Protocol using a rotation time of 0.5 sec • Half Scan reconstruction reduces to 0.25 sec (250 ms) • Phase Width or gate will be 250 ms • Leading edge of the phase placed at the Phase Start value and extends forward into the respiratory curve. • CT:  Phase Width is determined by temporal resolution of the protocol • PET:  Phase Width can be adjusted (not limited like CT) Examples of phase placement: • 10% • 50% Ex • 50% In • 90% TT Amplitude-Based Reconstruction • Selected as %In or %Ex in the Unit menu • Based on percentage of inhalation or exhalation (0% inhalation = 100% exhalation and vice versa) • Recommended to be used in the Anzai mode Phase-Based Reconstruction • Select %Pi in the Unit menu • Breathing signals provide the phase information • Only available in the open interface mode (Varian RPM) Amplitude-Based Reconstruction • Selected as %In or %Ex in the Unit menu • Recommended to be used in the Anzai mode Percent-Based Reconstruction • Select % in the Unit menu • Time based reconstruction that is calculated on fractions of the total length of the breathing cycle • One breathing cycle is from peak inspiration to peak inspiration (0-100%) CT Single Phase Reconstruction Example • Phase Start = 0 • Unit = %Ex PET Single Phase Reconstruction Example • Phase Start = 21 • Unit = %Ex • Phase Width = 35 (Phase Width uniqe to PET) Tip:  Left click/hold/drag across blue multi-phase bar to select multiple phases quickly. Multi-Phase Icon Hover the mouse over the Multi-Phase selection bar to display the selected phases. Multi-Phase Reconstruction • Allows multiple "single" phase reconstructions within a single reconstruction job • Images are reconstructed and stored in one series • Maximum number of phases per reconstruction job is 24 Multi-Phase Menu Tip:  Hover the mouse over the selection bar to display the selected phases. Gates • Utilizes up to a maximum of 24 gates CT Gate Definition:  Defined based on time between respiratory cycles • Cycle is divided evenly by the number of gates • Gate is placed in the center of each cycle • Gate width determined by temporal resolution Gate Centers at:  • Gate 1: 250ms • Gate 5:  2250ms • Gate 2:  750ms • Gate 6:  2750ms • Gate 3:  1250ms • Gate 7:  3250ms • Gate 4:  1750ms • Gate 8:  3750ms 15 RPM = 4000ms In Peak to In Peak 8 gates = 500ms/gate • Phase-matched PET and CT protocols support synchronization of gates • Typical protocol identical to non-matching counterpart but different trigger parameters • PET and CT trigger phases synchronize with Match CT enabled • PET and CT gates automatically align Recon Subtask Card • Extension of iterative reconstruction algorithm • Not available for back-projection Trigger Subtask Card • Unit:  OncoFreeze • Duty Cycle - Influences blurring but not image noise You have now completed the course Introduction to PET Respiratory Gating. You should now be able to: • Explain the concept and theory of respiratory gating in PET imaging • Describe the differences between phase based gating vs. amplitude based gating • Describe CT prospective and retrospective gating • Demonstrate the setup and usage of the Anzai Respiratory Gating system • Demonstrate the setup and usage of the Varian RPM and RGSc Respiratory Gating Systems • Describe how to acquire and reconstruct a respiratory gated study