kshama wechalekar consultant foundation
TRANSCRIPT
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Dr. Kshama WechalekarLead Consultant in Nuclear Medicine
Royal Brompton and Harefield NHS Foundation TrustLondon
Royal Brompton Hospital
PIOPED criteria –indeterminate results and different probability classifications
Overlap of anatomical segments
‘Shine‐through’ from underlying lung segments
Difficulties in visualising all lung segments
Difficult to interpret in patients with chronic heart and lung disease
Usually non‐diagnostic when chest X‐ray is abnormal
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Stein P, Freeman L et al JNM 2009
Identifies more and smaller mismatches
Has greater specificity & reduces interobserver variability
Improves localisation of defects and their size
Reduce indeterminate interpretation
Does not take longer than planar imaging
Generates images like planar, if desired
EANM Guidelines (2009) strongly recommend SPECT
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Investigators Year & Design Novelty Patients (n) Conclusion
Reinartz et al 2004Comparative VQ SPECT vs. CTPA (4 slice MDCT)
Planar images from SPECT by angular sampling method
83 patients assessed with different modalities.
Planar vs. SPECTSN ‐76%, 97%SP‐ 85%,92%Accuracy‐81%,94%
Miles et al 2009ProspectivePlanar and SPECT VQwith multislice CTPAscored with modified PIOPED for planar
New binary classificationSingle perfusion mismatch of 50%or >of a segment considered +vefor PE, any other pattern –ve.
10095% agreement rate between VQ SPECT and CTPANo PE for at least 3 months in –vestudies.
25% categorised as nondiagnostic20% as low5% as moderateNo non diagnostic studies on SPECT
Gutte et al 2009Prospective comparison of VQ‐SPECT VQ‐SPECT+Low dose CTCTPA with MDCT
First study directly comparing different modalities but on same scanner.Krypton‐81m as V agent
81 (38% PE)Final diagnosis by review of all clinical and imaging tests and 6 months follow up
Imaging SN SP
SPECT 97% 88%
SPECT+LDCT 97% 100%
CTPA MDCT 68% 100%
Low dose CT provides anatomical information such as atelectesis, emphysema, etc. Therefore abolishing the need for chest radiography and improving Sn, Sp and accuracy.
SPECT VQ is more sensitive owing to the better visualisation of effect of sub‐segmental embolisation
CTPA has a higher specificity due to direct visualisation of intraluminal clots and less prone to conditions that mimic embolism
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Leblanc M, Paul N. 2010
Need for a good ventilation agent
Setting up new protocols and training
Longer time slots initially‐?patient compliance
New hybrid software for analysis and quantification
Gaining expertise in SPECT interpretation
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99mTc‐DTPA Aerosol, Low cost, availability, commonly used, particle diameter of 0.5‐
1μm.
The biological T/2 varies from 80±20 min in healthy nonsmokers to 45±8
min in healthy passive smokers and 24±9 min in healthy smokers.
Central deposition in airways in COPD patients. 99mTechnegas Finer aerosol, better alveolar penetration and widely available in Europe.
Particle diameter about 0.005–0.2 µm. Distribution remain fixed for duration of study (Biological T/2 of 135 h)
Ideal for SPECT Hydrophobic but tend to grow by aggregation, and should be used within
10 min of generation.
True gas‐ No artefacts due to central airway deposition.
T/2 of 13 seconds‐ Inhaled 81mKr disappears from the alveolar space at a
much faster rate by decay than by exhalation. Regional alveolar 81mKr
concentration closely proportional to regional ventilation during steady
breathing.
Gamma energy of 191 keV‐ Ideal for gamma camera, simultaneous dual isotope study with MAA
Radiation dose‐ Extremely small, safe for children Production‐ 81Ru generator generator (T/2 81 Ru = 4.6 h), generator can be
used for 1 day.
Disadvantages‐ Limited access, high cost, need for a daily generator. Need for
continuous inhalation during acquisition.
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Tracer Administered
Activity‐(MBq)
Total Effective dose
Suitability for SPECT
99mTc‐MAA 200 2mSv
99mTc‐DTPA 80 0.4mSv
99mTechnegas 40 0.6mSv
81mKr 6000 0.2mSv
Values from ARSAC Notes for Guidance 2006
Technique Effective dose (mSv)
Single Slice LDCT 1mSv
CTPA 4 Slice 4.2mSv
CTPA 16 Slice 14.4 mSv
CTPA 64 Slice 19.9 mSv
Hurwitz et al 2006, ICRP 53, ICRP 80
Initial uncertainty
about transition
Planar and SPECT
acquisition sequentially (50 min)
Comparison of true
planar with derived
planars from SPECT
Confidence of
interpreters for derived images
SPECT VQ (25min)
SPECT + LDCT
(32min)
Plans for dual isotope 13.5 minPatient compliance
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Explanation of procedure No motion, tidal breathing Claustrophobia, inability to lie supine Ability to raise arms above head
Ventilation SPECT‐81mKr Adequate mask seal to prevent leakage Use of fan at foot end Avoid initial surge of Krypton
Perfusion SPECT 99mTc‐MAA 200MBq dose
Parameters Ventilation Perfusion
Camera Dual head camera GE Infinia Hawkeye
Collimator ELEGP
Matrix 128x128
Orbit 360, noncircular, Continuous /step and shoot
Projections 64x2=128
Tracer Krypton MAA
Time per projection 5 sec 10sec
Patient positioning Supine Inhalation during acquisition
Supine
Acquisition Positioning Supine with arms above the head if possible
LDCT Just before perfusion, arms above head Fixed tube voltage 140kv, Tube current 2.5mA
Current RBH protocol. Dual isotope protocols have described less number of projections
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If aerosols are used for ventilation, V first and then Q with 1:4 ratio of activity
If Kr‐81m is used for V, any order‐ but V first helps.
Simultaneous dual isotope study. (Check for downscatter)
Low dose CT for AC and anatomical localisation.
Additional Scatter window for AC (Synthetic map)
Respiratory Gating ( total counts but enhances defects)
Inspection of raw data for motion, wafting artefacts
Reconstruction Iterative‐ OSEM Filter ‐ Butterworth Normalisation of V to Q data Various softwares for registration and fusion (Hermes multi‐
modality imaging) V and Q data to be co‐registered to each other Co‐registration with LDCT/MDCT‐Motion of diaphragm and
heart prevent perfect registration. Triangulation in 3 orthogonal planes and MIP images
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VQ Quotient Identifies areas of mismatches Using a predetermined threshold, Q‐V (3D) Improves diagnostic accuracy Ability to see sub segmental mismatches
Localisation of Defects Orientation of 3D segmental anatomy Identification of defects in 3 orthogonal planes
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Ventilation
Perfusion
Quotient
Pulmonary sarcoidosis on treatment. Recent sudden SOB, CTPA -ve
67 year old female with chronic thrombo-embolism and PHT
Perfusion
Ventilation
Quotient
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Mass within left main bronchus
Ventilation
Perfusion
Quotient
Patient motion –Mis‐registration artefacts
Trapping of ventilation aerosols in emphysematous bullae causing mismatches.(Non‐segmental pattern)
Central deposition of DTPA aerosol in COPD patients.
Wafting artefact 81mKr –reconstruction artefact
MAA injection‐ aggregation of particles.
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Technical Advances‐Multi‐detector cameras and computing ability
VQ SPECT‐ Improved interpretationSubstantial improvement in accuracyReduced non‐diagnostic rates Ability to do regional quantification
CTPA – High radiation dose, contrast allergyHigh radiation dose to female breast
VQ SPECT should be the first line investigation in suspected acute PE
Algorithm for diagnostic imaging of patients suspected of acute PE
Pulmonary embolism guidelines Part 2 EANM 2009
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Advantages AC Some anatomical detail, effusion, tumour, fibrosis.
Single LDCT for V and Q SPECT Easier to fuse LDCT with MDCT if required.Disadvantages Small increase in time of acquisition and radiation burden ~ 1mSV{Total effective dose < 4mSv (CTPA~ 10mSv)}
Mis‐registration due to respiration and cardiac motion
Co‐registration of LDCT to MDCT
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K.Suga et al Annals of Nuclear med 2012
With dual head SPECT system, continuous rotating acquisition mode and pressure sensor respiratory tracking device for monitoring real time respiratory motion and time distance curves.
MDCT performed separately and fused.
Useful technique to resolve SPECT‐CTmis‐registration due to respiratory motion.
Needs training of patients to breathold for 20 sec.
Uses same MAA dose but longer acquisition time.
Improved understanding of functional and morphological correlation
Occasional dissociation of lung perfusion defect and intravascular clotsIncomplete obstruction of arterial branches by clots (seen on CTPA)
Failure of CTPA in visualising small clot fragments due to partial volume effect or cardiac motion
Insight into other pathologies such as lung infarction, COPD etc.
Proves superiority of Q SPECT.K.Suga et al Annals of Nuclear med 2012
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Mr. H.O.
84 year old male presenting with SOB
Known COPD
Ventilation
Perfusion
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Perfusion SPECT- CT
Ventilation SPECT-CT
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Perfusion
Ventilation
46 year old male
Known small cell lung cancer
For preoperative assessment of lung resection
MDCT 1 day prior
SPECT VQ fused with MDCT
Mass effect of tumour on vessels and airways
Possibility of doing lobar quantification
Ventilation
Perfusion
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Lung resection surgery pneumonectomy /lobectomy
Lung volume reduction surgery
Radical radiotherapy field planning.
Lung transplant and lung function after transplant
After surgery for complex congenital heart disease
Predicted post‐op FEV1= FEV1 X Predicted % of remaining lung (after surgery/ radiotherapy)
A postoperative or post‐RT FEV1= 700ml/min is required to avoid respirator dependence
51 patients with NSCLC
Potential impact of VQ SPECT over QSPECT alone was assessed to plan high dose RT vs. RT avoidance.
Abnormal VQ SPECT CT in all patients with tumour being most common and COPD as next cause of defect.
Most defects were matched but 31% patients had reverse mismatch(V<Q)
Low V regions contribute to low O2 saturation and therefore need to be incorporated in RT plan.
Shuanghu Yuan et al, Ann Arbor , University of Michigan J Thorac Oncol 2011
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Routine lung function tests FEV1>1.5 litre suitable for lobectomyFEV1>2.0 litre suitable for pneumonectomy
FEV1<1.5 litre (Lobectomy)< 2.0 litre (Pneumonectomy)
Quantitative lung scan
%ppo FEV1<40%%ppo TLCO<40%
Exercise testing VO2 max >15ml/kg/min
Surgery%ppoFEV1>40%%ppoTLCO>40%
VO2 max<15ml/kg/min Consider other options
BTS Guidelines 2001
Different techniques have been used to predict post‐operative lung function. These have included various pulmonary function tests and quantitative ventilation/perfusion scintigraphy. In practice, scintigraphy is not widely employed in assessing patients for lobectomy, because of the difficulty in interpreting the contribution of individual lobes to the overall ventilation or perfusion. This may explain why several investigators have reported that the simple calculation using lung segment counting can predict post‐operative FEV1 as accurately as ventilation/perfusion scintigraphy.
Perfusion scintigraphy is the most widely used method to predict post‐operative lung function in lung cancer patients undergoing pneumonectomy .
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Most lung cancer patients have MDCT
PACS, Data import and fusion software
Ability to see finer anatomical details
Future applications
Identification of interlobar fissures. Lobar definition and possibility
of improving quantification information in preoperative patients.
Improved understanding of disease processes.
More benefit for non‐PE applications, e.g. lung resection, LVRS,
radiotherapy planning.
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35% Contribution of RLL towards total perfusion Possible to quantify counts/vol of lung
Acquire Q SPECT+LDCT Co‐register V SPECT to LDCT Fused dataset
Identify fissures and define lobes on MDCT Fuse LDCT to MDCT
Transfer fissures on SPECT volumes of V and Q Calculate lobar quantification in 3D
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56 Y M
Known Emhysema
New lung mass in RUL
Preoperative assessment
Perfusion SPECT Ventilation SPECT
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Perfusion
Ventilation
Right lung
% Leftlung
%
RUL 6.4 LUL 48.3
RML 17.8
RLL 18.2 LLL 9.3
Total 42.4 57.6
Right lung
% Leftlung
%
RUL 5.4 LUL 34.5
RML 14.9
RLL 27.5 LLL 17.7
Total 47.8 52.2
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Comparison of post-lobectomy FEV1 with predicted FEV1 by planar and SPECT quantification
Spirometry
Surgery
Spirometry
Predicted ppo FEV1
Actual ppo FEV1