Dr. Kshama Wechalekar Lead Consultant in Nuclear Medicine Royal Brompton and Harefield NHS Foundation Trust London

Transcription

1 Dr. Kshama Wechalekar Lead Consultant in Nuclear Medicine Royal Brompton and Harefield NHS Foundation Trust London 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 1

2 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 2

3 Investigators Year & Design Novelty Patients (n) Conclusion Reinartz et al 2004 Comparative VQ SPECT vs. CTPA (4 slice MDCT) Planar images from SPECT by angular sampling method 83 patients assessed with different modalities. Planar vs. SPECT SN 76%, 97% SP 85%,92% Accuracy 81%,94% Miles et al 2009 Prospective Planar and SPECT VQ with multislice CTPA scored with modified PIOPED for planar New binary classification Single perfusion mismatch of 50%or >of a segment considered +ve for PE, any other pattern ve % agreement rate between VQ SPECT and CTPA No PE for at least 3 months in ve studies. 25% categorised as nondiagnostic 20% as low 5% as moderate No non diagnostic studies on SPECT Gutte et al 2009 Prospective comparison of VQ SPECT VQ SPECT+Low dose CT CTPA 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 3

4 Leblanc M, Paul N Need for a good ventilation agent Longer time slots initially?patient compliance Setting up new protocols and training New hybrid software for analysis and quantification Gaining expertise in SPECT interpretation 4

5 99m Tc 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. 99m Technegas Finer aerosol, better alveolar penetration and widely available in Europe. Particle diameter about 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 81m Kr disappears from the alveolar space at a much faster rate by decay than by exhalation. Regional alveolar 81m Kr 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 81 Ru 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. 5

6 Tracer Administered Activity (MBq) Total Effective dose 99m Tc MAA 200 2mSv Suitability for SPECT 99m Tc DTPA mSv 99m Technegas mSv 81m Kr mSv 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 min Patient compliance 6

7 Explanation of procedure No motion, tidal breathing Claustrophobia, inability to lie supine Ability to raise arms above head Ventilation SPECT 81m Kr Adequate mask seal to prevent leakage Use of fan at foot end Avoid initial surge of Krypton Perfusion SPECT 99m Tc 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 7

8 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 multimodality 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 8

9 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 9

10 Pulmonary sarcoidosis on treatment. Recent sudden SOB, CTPA -ve Ventilation Perfusion Quotient 67 year old female with chronic thrombo-embolism and PHT Perfusion Ventilation Quotient 10

11 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 81m Kr reconstruction artefact MAA injection aggregation of particles. 11

12 Technical Advances Multi detector cameras and computing ability VQ SPECT Improved interpretation Substantial improvement in accuracy Reduced non diagnostic rates Ability to do regional quantification CTPA High radiation dose, contrast allergy High 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

13 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 13

14 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 CT mis registration due to respiratory motion. Needs training of patients to breathold for 20 sec. K.Suga et al Annals of Nuclear med 2012 Uses same MAA dose but longer acquisition time. Improved understanding of functional and morphological correlation Occasional dissociation of lung perfusion defect and intravascular clots Incomplete 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

15 Mr. H.O. 84 year old male presenting with SOB Known COPD Ventilation Perfusion 15

16 Perfusion SPECT- CT Ventilation SPECT-CT 16

17 Perfusion 46 year old male Known small cell lung cancer For preoperative assessment of lung resection MDCT 1 day prior Ventilation SPECT VQ fused with MDCT Mass effect of tumour on vessels and airways Possibility of doing lobar quantification Ventilation Perfusion 17

18 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

19 Routine lung function tests FEV1>1.5 litre suitable for lobectomy FEV1>2.0 litre suitable for pneumonectomy FEV1<1.5 litre (Lobectomy) < 2.0 litre (Pneumonectomy) Quantitative lung scan %ppofev1>40% %ppotlco>40% Surgery %ppo FEV1<40% %ppo TLCO<40% Exercise testing VO 2 max >15ml/kg/min VO 2 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 FEV 1 as accurately as ventilation/perfusion scintigraphy. Perfusion scintigraphy is the most widely used method to predict postoperative lung function in lung cancer patients undergoing pneumonectomy. 19

20 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. 20

21 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 21

22 56 Y M Known Emhysema New lung mass in RUL Preoperative assessment Perfusion SPECT Ventilation SPECT 22

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24 Ventilation Right lung % Left lung % RUL 6.4 LUL 48.3 RML 17.8 RLL 18.2 LLL 9.3 Total Right lung % Left lung % RUL 5.4 LUL 34.5 RML 14.9 RLL 27.5 LLL 17.7 Total Perfusion 24

25 Comparison of post-lobectomy FEV1 with predicted FEV1 by planar and SPECT quantification Spirometry Surgery Spirometry Actual ppo FEV1 Predicted ppo FEV1 25