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.