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Movimento Respiratorio in Diagnostica e Radioterapia:un problema risolto?
Quale impatto sulla Diagnostica ?
V.BettinardiNuclear Medicine Dep.
Scientific Institute San Raffaele
PET motion issues
The radioactivity distribution of a lesion is smeared over the volume of motion resulting in a :- degradation of the image quality (e.g. reduction of the contrast )- underestimation of the tracer uptake ( activity concentration, SUV) - overestimation of the lesion volume
Liver Heart Lung
Respiratory motion of organs is complex because It consists of variable combination of different mechanisms: translation rotation and deformation
The magnitude of the respiratory organ motion is different for different organs
The magnitude of the respiratory organ motion is different among patients
Respiratory Gating Techniques4D PET/CT
Respiratory Monitoringsystem
Respiratory organ motion can be accounted by using the Respiratory Gating 4D-PET/CT acquisition techniques which are characterized by the syncronization of the acquired data to the patient respiratory cycle.
The aim of a 4D-PET/CT study is to obtain respiratory motion freeCT and PET images as well as well aligned CT and PET images
4D-PET/CTAcquisition Protocol
4D-PET/CT study
+
WB Helical CTWB 3D PET
Frame Mode Acq.
2-2.5 min
2-2.5 min
2-2.5 min
2-2.5 min
2-2.5 min
2-2.5 min
4D-PET/CTAcquisition Protocol
4D-PET/CT (one PET FOV)
on a selected anatomical region
4D-CT
4D-PET
12 min Total Acq. Time24 - 27 min
This protocol is used:-for characterization of small
nodules ..detected by CT-when the physicians have a doubt
..about the PET finding in the conventional WB PET - for all the RT applications
Technical characteristics of the 4D-CT and 4D-PET acquisitions
RPM Signal
……
CT Acq.First Position
ScanSecond Position
Scan Scan
4D-CT
RPM Signal
……
CT Acq.First Position
ScanSecond Position
Scan Scan
4D-CT
RPM Signal
T T T
4D-PET
List Mode Acq. registration of each single event as: X,Y,Z, Time, Energy etc.etc..
RPM Signal
T T T
4D-PET
List Mode Acq. registration of each single event as: X,Y,Z, Time, Energy etc.etc..
Six CT gates
Each 4D-PET gate isreconstructed by using for AC the corresponding 4D-CT gate
4D-PET/CT Phase Matched Reconstruction
Six PET raw datagates
Six PET gates
PET Reconstruction
4D-PET/CT
The aim of a 4D PET/CT study is to obtain a Respiratory motion free CT and PET images
as well aswell aligned CT and PET images
Clinical Expectationfrom 4D-PET/CT
• Improving quantification• Improving confidence in reporting• Improving lesion detectability• Improving patient management
4D-PET: Phase 5
Sphere : 8 mm diameterActivity Ratio between Lesion and Background : 4 to 1
PET Static Acquisition
0
0,2
0,4
0,6
0,8
1
1,2
1,4
0 20 40 60 80 100 120Pixel Number
Rad
. Con
c. (
Ci/c
c)
PET StaticPET with Motion4D-PET
- 3,6%
- 42.5%
Axial Motion of the SphereDisplacement = 1cm
HSR Milano
4D-PET/CT well aligned PET and CT images
WB PET/CT Standard 4D-PET/CT
Single Gate
SUVmax = 3.1 SUVmax = 4.2
Mismatch between PET and CT images due to the patient’s respiration.
4D-PET/CT: More accurate spatial and temporal correlation .
HSR Milano
Improving confidence in reporting
SUV=2.0 SUVPhase4=3.2
SUV=1.6 SUVPhase4=2.9
HSR Milano
EFFECT OF PATIENT RESPIRATION ON THE MEASURED UPTAKE VALUES IN THE CHARACTERIZATION OF PULMONARY NODULES BY 4D-PET/CT
Twenty-six consecutive oncological patients (pts) referred for the characterization of pulmonary nodules (PN) were studied (n=42)
Lesion displacement
CONCLUSIONSUVmax resulted significantly higher in the 4D-PET phases than in the in PET baseline study (mean + 33% +/- 13).
Mean 3.4 mm SD 08
Mean 6.6 mm SD 2.0
Mean 11.7 mm SD 2.6
SUVmax was measured for each nodules on the static WB-PET (Baseline) and over all six bins of the 4D-PET data The six SUVmax were then averaged
The SUVmax for all PNs always resulted lower in the conventional PET baseline study when compared to the average of the six SUVmax of the 4D-PET data.
HSR Milano
WB PET STANDARD
4D PET
Improving confidence in reporting
HSR Milano
Example of integrated 4D PET/CT improving confidence in reporting and lesion detectability
420504 CRC restaging for liver mts
Equivocal liver finding: a third mets?
Example of integrated 4D PET/CT improving confidence in reporting and lesion detectability
420504 CRC restaging for liver mts
Example of integrated 4D PET/CT improving confidence in reporting and lesion detectability
420504 CRC restaging for liver mts
SUVmax 3.0
SUVmax 3.5
BIN 3
Dual Points PET measurements
• Lesion Shape and Volume do not change• Patient respiration could be different --> lesion
motion could be different• PET/CT mismatch could be different
Expectation : Accurate evaluation of the tracer uptake changes over time
Follow up PET studies
• Lesion Shape and Volume could be different different PVE• Patient Respiration could be different Lesion motion could
be different• PET/CT mismatch could be different
Expectation : An accurate evaluation of the effect of the treatment …..
November:2007Lesion Diameter : 1.5cmSUVmax: 3.0
January: 2008Lesion Diameter : 1.5cmSUVmax: 3.1
January: 2008Lesion Diameter : 1.5 cm4D-SUVmax: 4.2Lesion Displacement: 9 mm
HSR Milano
Pre –RT TreatmentLesion Diameter : 1.5 cm4D-SUVmax: 4.2Lesion Displacement: 9 mm
Post –RT Treatment“Lesion” Diameter : 5.5 mm4D-SUVmax: 0.9Lesion Displacement: 1.4 cm
PET/CT 1y after
treatmentHSR Milano
Summary
• Organ/Lesion movement is one of the most important factor affecting Image Quality and the Quantitative Accuracy of PET/CT images
• 4D PET/CT allows to account and compensate for organ/lesion movements related to the patient breathing
• The use of 4D PET/CT could be useful to improve diagnostic applications.