Introduction to Respiratory Gating in PET/CT
This web based training will provide information to the PET technologist who is new to respiratory gating. The topics of this presentation include: Why respiratory gating, phase based gating (4D PET), amplitude based gating (HD·Chest), CT respiratory gating, respiratory gating using the Anzai device, respiratory gating using the Varian RPM device, respiratory gated acquisition, and respiratory gated reconstruction.
In this web-based training, you will become more familiar with Respiratory Gating in PET/CT. This course will take approximately 45 minutes to complete. Demonstrate the setup and usage of the Anzai and Varian respiratory gating systems. Describe how to acquire and reconstruct a respiratory gated study. Discuss CT prospective and retrospective gating. Explain the concept and theory of respiratory gating in PET imaging. List the differences between phase based gating and amplitude based gating. By the end of this web-based training, you will be able to: HD-Chest Another name for amplitude-based gating Attenuation Correction Improved by aligned PET and CT gates Reasons for respiratory gating I. Motion complicates the diagnosis of respiratory lesions II. Overestimation of lesion volume III. Underestimation of SUV Spiral Acquisition Used in CT retrospective reconstruction Anzai system Supports both phase and amplitude gating Varian RPM respiratory gating Video-based Amplitude-based gating Calculation always selects 35% of all acquired data Anzai Load Cell Calibration Should be performed once a year Phase-Based Gating Measurements based on the signals from the strain of the belt around the patient’s abdomen Anzai deep sensitivity Best to use on deep-breathing patients 1. Select the AZ733VI icon to start the software. 2. In the Patient Information field, select the Patient File Management icon to open the Patient File Management window. Load Cell Fixing Belt Available in 4 sizes: XS, S, M, L, LL Load Cell or Pressure Sensor Two versions: Deep (best for deep breathing patients) Standard (best for regular or shallow breathing patients) Load Cell technology Supports both phase and amplitude gating Used for capturing and storing a signal representing patient’s respiratory cycles CT Prospective Gating Gating Switch box set to Trigger Mode TRIGGER MODE WAVEFORM MODE CT and PET Retrospective Gating: Set to Waveform mode The Anzai laptop is not needed for this type of gating 1. Place appropriate cell in pouch of belt with the label “Standard” or “Deep” facing outward. 2. The pink dot on this image shows the approximate area where the load cell should be placed. 3. Place the belt around the patient’s chest with the load cell close to the rib or other firm structure. Position Adjustment Dial LCD Screen: Patient's respiratory waveform is displayed and instantly adjustable. Magnification Adjustment Dial Real-time Position Management (RPM) Non-invasive Video based Clean imaging and treatment of lung, breast, and upper abdominal sites Supports both phase and amplitude gating Marker Block Placed on the patient to follow the patients breathing Allows tracking of the motion Infrared Camera Tracks the Marker Block and records the motion of the device Informs the software that an external unknown gating device will be used for respiratory gating To activate: Options Configuration Respiratory Gating Open Interface PET Gating Starts after topogram and CT scan, and prior to the PET acquisition Varian Software UI: Select Record Start the PET acquisition and allow to complete Stop the Varian gating and save the .vxp file for import with a unique name for PET dataset Import the .vxp files Waveform is present in the Trigger card File Importing Options 1. Network Share When logged in as meduser, create a new directory on your H drive Partition and share the directory 2. USB Copy and transport to MI Acquisition Workstation Importing the file through the Trigger subtask card UI: 1. Open the Trigger subtask card 2. Click the Import button 3. Locate and click on the .vxp file in the directory 4. Click Import 1. Register the patient. 2. Define the study: RespiratoryGated, or RespiratoryGatedCBM. 3. Select Exam. 4. Position the patient. 5. Attach the respiratory gating device. 6. Acquire the scan. 7. Gated PET can be Step and Shoot or CBM. Phase match synchronization of gates for both CT and PET respiratory gating CT and PET gates are automatically aligned for improved AC Can be used for Step and Shoot or CBM Requires a respiratory gating device Single Phase / Multi-Phase Reconstructs a single phase at the specified location in the respiratory cycle Starts between 0-100% Respiratory Motion Complicates diagnosis of thoracic lesions Causes errors in definition of target volumes in RTP 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 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 that get rejected Some bad triggers do not get rejected Variable breathing patterns Gate 1 Max. Inhalation Gate 3 Mid Exhalation Gate 6 Max. Exhalation PET emission data and respiratory wave form data are recorded simultaneously Reconstruction is always retrospective *Supports the following reconstructions in the same protocol: Single-phase Multi-phase Gates Motion Frozen Anzai or Varian RPM systems Laptop is not needed for the Anzai system Much of the setup can be performed at the MI Acquisition Workstation *Dependent upon licensing Sequential, non-spiral Triggered by 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 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 Laptop Computer Windows 7 platform It is used for CT prospective gating only Sensor Port Monitors and triggers respirations Amplifies the respiratory signal Relay Box Used to transfer the data between the Sensor Port and Personal Computer Gate Disable Switch Suspends gate output in case of emergency 4. Place patient on the table and position for exam. 5. Plug Load Cell into Sensor Port. 6. Check LED sensors. Green — proper tension Red Tight — loosen belt Red Loose — tighten belt 3. Select the Patient Entry icon to activate the Patient Information field. 4. Enter patient information into the Patient Information fields. a.The ID number and the name are mandatory fields. 5. Select the Save button to save the entry. 6. Select the Cancel button to cancel the registration. 7. The patient 's name will appear in the patient list. 8. Highlight the patient's name in the list and select the Load Patient Information icon to load the patient into the main screen. 9. Affix the belt and load sensor to the patient and position them on the table. 10. Check the waveform. a. If the waveform is not positioned correctly, use the position and magnification adjustments to correct. b. Another option is to use the Auto buttons to make an auto correction. 11.Select the Setting Lock icon. a. Locks the following settings: i. Patient Registration ii. Respiratory Waveform Adjustment iii. Gate Signal Output 12. Select the Start icon to start the data acquisition. 13. Select the Gate On/Off icon. 14. A gate output confirmation dialog window displays. a. Enter for Yes b. Esc for No 15. When the acquisition has ended, select the Stop button. 16. A confirmation window appears. Select Yes or No. Phase-Based Gating Multiphase Mode – On Single-phase Mode - Off Gating Interface Box Connects the Infrared camera to the workstation RPM Workstation Houses software Allows monitoring of gate signals PROSPECTIVE CT Gating: Starts after topogram and prior to the CT scan Varian Software UI: Select Record and Enable Gating Provides the Trigger (x-ray ON) signal to CT gantry Start CT scan and allow to complete Stop Varian gating No need to save .vxp file Trigger card is not present in prospective CT protocol RETROSPECTIVE CT Gating Starts after the topogram and prior to CT Scan Varian Software UI: Select Record Start the CT scan and allow it to complete Start the CT scan and allow it to complete Stop the 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 in present Waveform not viewable until imported from Varian system Imported .vxp file will populate the Trigger subtask card Temporal resolution of CT can result in gaps between CT gates Match CT Enabled Centers of PET gates will match the CT gates Phase width is not the same Gates Utilizes up to 24 gates (maximum) 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 PET gate definition: Follows similar rules but is not limited by temporal resolution PET gate spans the entire cycle with no gap HD·Chest (PET Only) Amplitude-based method Respiratory waveform is stored along with list mode data Computer program analyzes the entire waveform to determine optimal area of least respiratory motion within the waveform Phase width allows you to change the relative duration of the gate to accept more or less respiratory motion In this course, we covered: The concept and theory of respiratory gating in PET imaging Differences between phase-based gating and amplitude-based gating Specific components of CT prospective and retrospective gating The setup and use of the Anzai and Varian Respiratory Gating systems The acquisition and reconstruction of a respiratory gated study Next: Course Review and Course Assessment Minimum passing score for assessment: 80 In the case of Load Cell (Low) Tuning Zero Adjustment Trimmer Zero Adjust LED Max R. R. Clockwise: 20 R. R. Counterclockwise: 20 R. R. Caution: In both directions, the trimmer can be turned over 20 R. R., but it does not affect adjustment any more. See more image and detail on the next page. Load Cell Calibrator Load Cell Flat Surface 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 semiquiescent period between breaths. Optimal Imaging Region inhale exhale Signal related to patient’s breathing Measurements based on signals strain gauge belt worn around the patient’s chest or abdomen while lying supine on table Load cell senses the strain and the response generates a voltage level Waveform produced Expiration Inspiration Variable Breath Amplitude Changing Baseline Breath Amplitude Time Some breaths are deeper than others (Variable Breath Amplitude curve) Relaxed position between breaths does not always give the same signal. (Changing Baseline curve) Breath Amplitude Expiration Inspiration Variable Breath Amplitude Changing Baseline Time Like 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 Breath Amplitude Measure PET data not used Measure PET data not used Measure PET data inappropriately combined Inappropriate Trigger-rejected Inappropriate Trigger-rejected Inappropriate Trigger-kept Also marketed as *HD·Chest or Waveform Gating Computer analyzes the entire waveform to determine the optimal part of the waveform Calculation always selects 35% of all the acquired data Images are created from data when waveform is higher than the lower threshold but lower than the upper threshold Optimal Gate Upper Level U Lower Level U Time Respiratory Waveform Respiratory Histogram Inspiration & Expiration Reference Points Modify Waveform Multiphase Button Adjust Gain Adjust Offset Return to Normal Display Modify Waveform Use Gain and Offset sliders to make adjustments Trigger Method HD·Chest (Waveform) Trigger Mode Waveform Mode