Radionuclide Radionuclide Pulmonary imagingPulmonary imaging(LUNG V/Q SCAN)(LUNG V/Q SCAN)Radiology Resident Half Radiology Resident Half

Academic DayAcademic Day

Dr Hussein FarghalyDr Hussein Farghaly

Nuclear Medicine Nuclear Medicine ConsultantConsultant

PSMMCPSMMCRiyadh, KSA March, 2011

Clinical Application:Clinical Application:

• A. The most common clinical indication for lung scintigraphy is to A. The most common clinical indication for lung scintigraphy is to determine the likelihood of pulmonary embolism (PE).determine the likelihood of pulmonary embolism (PE).

• B. Less common clinical indications are:B. Less common clinical indications are:

1. Document the degree of resolution of pulmonary embolism1. Document the degree of resolution of pulmonary embolism

2. Quantify differential pulmonary function before pulmonary surgery for lung 2. Quantify differential pulmonary function before pulmonary surgery for lung cancer cancer

3. Evaluate lung transplants 3. Evaluate lung transplants

4. Evaluate congenital heart or lung disease such as cardiac shunts, 4. Evaluate congenital heart or lung disease such as cardiac shunts, pulmonary arterial stenosis, and arteriovenous fistulae and their treatment pulmonary arterial stenosis, and arteriovenous fistulae and their treatment

5. Confirm the presence of bronchopleural fistula 5. Confirm the presence of bronchopleural fistula

6. Evaluate chronic pulmonary parenchymal disorders such as cystic fibrosis6. Evaluate chronic pulmonary parenchymal disorders such as cystic fibrosis

7. Evaluate the cause of pulmonary hypertension 7. Evaluate the cause of pulmonary hypertension

PROCEDURE/SPECIFICATIONS OF THE PROCEDURE/SPECIFICATIONS OF THE EXAMINATIONEXAMINATION

• Nuclear Medicine study request:Nuclear Medicine study request: -Women of childbearing age-Women of childbearing age

-Clinical pre test probability of PE (Wells score)-Clinical pre test probability of PE (Wells score)

-D-Dimer test-D-Dimer test

-History of prior DVT or PE or anticoagulant therapy-History of prior DVT or PE or anticoagulant therapy

-Review of prior lung scintigraphy-Review of prior lung scintigraphy

-Relevant chest radiographic findings-Relevant chest radiographic findings

• Patient Preparation and PrecautionsPatient Preparation and Precautions -A standard chest X-ray CT scan can substitute-A standard chest X-ray CT scan can substitute

- Pregnant or breastfeeding women: benefit versus risk.- Pregnant or breastfeeding women: benefit versus risk.

- Discontinue breastfeeding for 24 hours - Discontinue breastfeeding for 24 hours

- Children < 3 years of age: Limit close contact for 24 - Children < 3 years of age: Limit close contact for 24 hours. hours.

Perfusion scan: Perfusion scan: Agent:Agent:

• Tc-99m macro-aggregated albumin (Tc-99m MAA)Tc-99m macro-aggregated albumin (Tc-99m MAA)

• Particle size: 10-90 microns (90% of particles)Particle size: 10-90 microns (90% of particles)

• No particles should be larger than 150 micronsNo particles should be larger than 150 microns

• Obstructing ~ 0.1% of precapillary arteriolesObstructing ~ 0.1% of precapillary arterioles

• Particles clearance: Enzymatic hydrolysis and Particles clearance: Enzymatic hydrolysis and

phagocytized by reticuloendothelial cells (biologic half-phagocytized by reticuloendothelial cells (biologic half-

life of 6-8 hours). life of 6-8 hours).

• Critical organ: Lungs, 1 rad/5 mCi Total RDE : ~ 0.8 mSvCritical organ: Lungs, 1 rad/5 mCi Total RDE : ~ 0.8 mSv

Number of particles: Number of particles: 500,000500,000 particles/5mCi, Minimum of particles/5mCi, Minimum of 70,000 70,000

Reduced number of particles:Reduced number of particles:

100,000100,000 in Pulmonary arterial hypertension (> 50 mmHg), right to in Pulmonary arterial hypertension (> 50 mmHg), right to left shuntsleft shunts, , status post pneumonectomy, poor respiratory status post pneumonectomy, poor respiratory function, cardiopulmonary instability.function, cardiopulmonary instability.

10,000 to 50,000 10,000 to 50,000 particles in Neonates:particles in Neonates:• Neonate have about 10% of adult pulmonary capillariesNeonate have about 10% of adult pulmonary capillaries• Number of capillaries increases to half of the adult value by age Number of capillaries increases to half of the adult value by age

3 years, and reaches an adult level by age 8 to 12 years.3 years, and reaches an adult level by age 8 to 12 years.

• Dose and adminstraion: Dose and adminstraion: Adult 40–150 MBq (1–Adult 40–150 MBq (1–4 mCi). Pediatric 1.11 MBq/kg (0.03 mCi/kg) with a minimum of 4 mCi). Pediatric 1.11 MBq/kg (0.03 mCi/kg) with a minimum of 14.8 MBq/kg (0.4 mCi)14.8 MBq/kg (0.4 mCi)

- Tc-99m MAA is injected IV slowly during 3–5 respiratory cycles - Tc-99m MAA is injected IV slowly during 3–5 respiratory cycles with the patient in the supine position..with the patient in the supine position..

--

Perfusion scan: Perfusion scan: AgentAgent cont.cont.::

Perfusion scan: Perfusion scan: ImagingImaging

• Imaging is preferably performed in the upright position to increase Imaging is preferably performed in the upright position to increase chest cavity size and to minimize diaphragmatic motion.chest cavity size and to minimize diaphragmatic motion.

• Large field of view camera, parallel hole and high-resolution Large field of view camera, parallel hole and high-resolution collimator. Planar images should be obtained in multiple projections collimator. Planar images should be obtained in multiple projections including anterior, posterior, both posterior oblique, both anterior including anterior, posterior, both posterior oblique, both anterior oblique and both lateral projectionsoblique and both lateral projections

• SPECT can be used to obtain a three-dimensional evaluation of SPECT can be used to obtain a three-dimensional evaluation of the perfusion, and is recommended by some investigators.the perfusion, and is recommended by some investigators.

• Images of the brain may be obtained to distinguish right-to-left Images of the brain may be obtained to distinguish right-to-left shunting from systemic distribution of radiopharmaceutical shunting from systemic distribution of radiopharmaceutical components too small to be trapped by capillaries. components too small to be trapped by capillaries.

• Tc-99m MAA injection into the veins of the feet: May help to reveal Tc-99m MAA injection into the veins of the feet: May help to reveal a DVT as "hot spots" Venous obstruction or collateral flow can be a DVT as "hot spots" Venous obstruction or collateral flow can be seenseen

Tc-99m MAA Perfusion Lung Tc-99m MAA Perfusion Lung ScanScan

RADIOACTIVE GASES:RADIOACTIVE GASES: - Xenon-133 (5 days, 81KeV ) - Xenon-133 (5 days, 81KeV )

- Krypton-81m (13 sec, 190 KeV, RU-81/Kr-81m generator- Krypton-81m (13 sec, 190 KeV, RU-81/Kr-81m generator))

RADIOAEROSOL:RADIOAEROSOL: --Technegas “pseudo-gas (0.005–0.2 μm) Technegas “pseudo-gas (0.005–0.2 μm)

-Tc-99m DTPA aerosol (0.1–0.5 μm)-Tc-99m DTPA aerosol (0.1–0.5 μm)

Ventilation scan: Ventilation scan: RadiopharmaceuticalsRadiopharmaceuticals

Ventilation scan:Ventilation scan: Xenon-133Xenon-133• Gamma energy: 81 keVGamma energy: 81 keV• Physical half-life: 5.2 daysPhysical half-life: 5.2 days• Dose inhaled: 15-25 mCi through Xenon delivery Dose inhaled: 15-25 mCi through Xenon delivery

device. device. • Critical organs: Trachea and airways of ~ 250 mradCritical organs: Trachea and airways of ~ 250 mrad• Absorbed dose by the body: Less than 15% Absorbed dose by the body: Less than 15% • Total radiation dose equivalent: 1.2 -2.0 mSvTotal radiation dose equivalent: 1.2 -2.0 mSv• Xe-133 ventilation scan performed prior to Q scan Xe-133 ventilation scan performed prior to Q scan • Uncommon practice: Xe-133 exam after the Uncommon practice: Xe-133 exam after the

perfusion study; low dose of Tc-99m MAA first (1-2 perfusion study; low dose of Tc-99m MAA first (1-2 mCi) and then high dose of Xe-133 (20-30 mCi)mCi) and then high dose of Xe-133 (20-30 mCi)

• Gamma camera placed behind the patient's back: Posterior view.Gamma camera placed behind the patient's back: Posterior view.• Xe-133 is inhaled through a mouthpiece of the Xenon delivery Xe-133 is inhaled through a mouthpiece of the Xenon delivery

system. system.

Ventilation scan in 3 phases: Ventilation scan in 3 phases: • Single breath: Single breath: At maximum inspiration take 10-15 sec image. At maximum inspiration take 10-15 sec image.

COPD detected in ~ 66% COPD detected in ~ 66% • Equilibrium: Equilibrium: Normal tidal respirations for 3-5 minutes, rebreathing Normal tidal respirations for 3-5 minutes, rebreathing

a mixture of Xenon-133 and oxygen take two sequential 90 sec a mixture of Xenon-133 and oxygen take two sequential 90 sec images. Least sensitive for COPD diagnosis. images. Least sensitive for COPD diagnosis.

• Washout: Washout: Patient breaths room air or oxygen while exhaling the Patient breaths room air or oxygen while exhaling the xenon into a charcoal trap take three sequential 45 sec images. xenon into a charcoal trap take three sequential 45 sec images. Biological half life is 30 sec.Biological half life is 30 sec.

• Normal Xenon-133 clearance: 2-3 minutes. Clearance > 3 minutes: Normal Xenon-133 clearance: 2-3 minutes. Clearance > 3 minutes: Air trapping. More sensitive (90%) than single breath phase in Air trapping. More sensitive (90%) than single breath phase in diagnosing COPD. diagnosing COPD.

• Xenon more sensitive than aerosolized Tc-DTPA for detecting COPD. Xenon more sensitive than aerosolized Tc-DTPA for detecting COPD.

Ventilation scan:Ventilation scan: Xenon-Xenon-133133

Xenon ventilation scan

Ventilation scanVentilation scan: : Krypton-Krypton-81m81m

• Rubidium krypton-81m generator. Rubidium krypton-81m generator. • Isomeric transition like Tc-99mIsomeric transition like Tc-99m• Gamma emission: 191 keV (65%)Gamma emission: 191 keV (65%)• Physical half-life: 13 secondsPhysical half-life: 13 seconds

Advantages:Advantages:• Higher energy than Tc-99mHigher energy than Tc-99m• Very short physical half-life: V imaging immediately after each Q imageVery short physical half-life: V imaging immediately after each Q image• Radiation dose to the lungs is lower than with other agents (about 15 mrad Radiation dose to the lungs is lower than with other agents (about 15 mrad

per view). per view).

Disadvantages: Disadvantages: • Rubidium 81m: Physical half-life ~ 4.5 hours, can be used only for 1 day Rubidium 81m: Physical half-life ~ 4.5 hours, can be used only for 1 day

• Limited assessment of COPD because tracer decays before an equilibrium Limited assessment of COPD because tracer decays before an equilibrium distribution can be attaineddistribution can be attained

Ventilation scan: Ventilation scan: Tc-99m Tc-99m DTPADTPA• Submicronic particles (aerosols) inhaled through an Submicronic particles (aerosols) inhaled through an

aerosol delivery system.aerosol delivery system.

• Particles size: 0.5 to 0.8 microns in diameter, Particles size: 0.5 to 0.8 microns in diameter, reaching alveolireaching alveoli

• Dose: 30 mCi (3-5 minutes rebreathing within closed Dose: 30 mCi (3-5 minutes rebreathing within closed system, oxygen at 8-10 liters/min).system, oxygen at 8-10 liters/min).

• System delivers about 0.5-0.8 mCi of tracer to the System delivers about 0.5-0.8 mCi of tracer to the lungs 100,000 counts images in about 2-5 minutes.lungs 100,000 counts images in about 2-5 minutes.

• Radiation exposure to the lungs: ~ 100 mrads. Radiation exposure to the lungs: ~ 100 mrads.

• Exposure to personnel: Less compared with Xenon Exposure to personnel: Less compared with Xenon study. study. 

• Half-time clearance: 1-1.5 hours in normal patients; Half-time clearance: 1-1.5 hours in normal patients; more rapid clearance in patients with PE, lung injury more rapid clearance in patients with PE, lung injury (ARDS), pulmonary fibrosis, and in smokers (20 min.) (ARDS), pulmonary fibrosis, and in smokers (20 min.)

Tc-99m DTPA vs. Xe-133Tc-99m DTPA vs. Xe-133

Advantages of Tc-99m DTPA Advantages of Tc-99m DTPA : :

• No collection devices for exhaled gasNo collection devices for exhaled gas

• Multiple projectionsMultiple projections

• Can perform before or after perfusion Can perform before or after perfusion scanscan

• Feasible for ICU patients on ventilatorFeasible for ICU patients on ventilator

Disadvantage of Tc-99m DTPA Disadvantage of Tc-99m DTPA ::

• Air trapping cannot be assessed.Air trapping cannot be assessed.

• Xenon more sensitive than Tc-DTPA for Xenon more sensitive than Tc-DTPA for detecting COPD. detecting COPD.

Ventilation scan: Ventilation scan: Tc-99m Tc-99m technegastechnegas• Tc-04 is vaporized in a microfurnace: Ultrafine Tc-04 is vaporized in a microfurnace: Ultrafine

labelled carbon particles.labelled carbon particles.

• Particle size: 0.05 and 0.15 micronsParticle size: 0.05 and 0.15 microns

• Good peripheral deposition: even in COPD.Good peripheral deposition: even in COPD.

• Longer pulmonary retention no effective Longer pulmonary retention no effective clearance half time is 6hrsclearance half time is 6hrs

• The material is produced by heating 5mCi The material is produced by heating 5mCi

of Tc- pertechnetate to very high temperaturesof Tc- pertechnetate to very high temperatures

(2500 degrees Celsius) in the presence of (2500 degrees Celsius) in the presence of

100% argon gas produced a Tc-carbon 100% argon gas produced a Tc-carbon

particle that is so small it acts like a gas. particle that is so small it acts like a gas.

Image Sequence:

• A. A chest radiograph should be obtained and reviewed A. A chest radiograph should be obtained and reviewed before lung scintigraphy.before lung scintigraphy.

• B. Ventilation scintigraphy using 133Xe is usually performed B. Ventilation scintigraphy using 133Xe is usually performed before perfusion scintigraphy. Alternately, perfusion before perfusion scintigraphy. Alternately, perfusion scintigraphy can be performed first and ventilation scintigraphy can be performed first and ventilation scintigraphy omitted if not needed.scintigraphy omitted if not needed.

• C. Because of the higher energy of the gamma emissions and C. Because of the higher energy of the gamma emissions and the short half-life of 81mKr, images obtained with this gas the short half-life of 81mKr, images obtained with this gas can be alternated with those obtained with 99mTc MAA.can be alternated with those obtained with 99mTc MAA.

• D. When 99mTc labeled aerosol imaging is performed before D. When 99mTc labeled aerosol imaging is performed before 99mTc MAA perfusion imaging, smaller amounts (20-40 MBq) 99mTc MAA perfusion imaging, smaller amounts (20-40 MBq) [0.5-1.0 mCi]) of 99mTc labeled aerosol should be [0.5-1.0 mCi]) of 99mTc labeled aerosol should be administered to the lungs.administered to the lungs.

Normal Ventilation/Perfusion

ACUTE PULMONARY EMBOLISMACUTE PULMONARY EMBOLISM

CLINICAL PRESENTATION: (Non-CLINICAL PRESENTATION: (Non-specific)specific)

• Haemoptysis, Dyspnea and Pleuritic Haemoptysis, Dyspnea and Pleuritic Chest pain (Virchows triad)Chest pain (Virchows triad)

• Back or Abdominal pain, cough, SOB, Back or Abdominal pain, cough, SOB, Low-grade fever,----------Low-grade fever,----------

• May be asympotmaticMay be asympotmatic

EvaluationEvaluation

• ABG – Respiratory alkalosis, hypoxiaABG – Respiratory alkalosis, hypoxia

• ECG – Sinus tachycardia & S1Q3T3ECG – Sinus tachycardia & S1Q3T3

• D-Dimer D-Dimer

• CXRCXR

• Spiral CT with contrastSpiral CT with contrast

• V/Q ScanV/Q Scan

• AngiogramAngiogram

Question 1Question 1

Pulmonary angiography as “gold Pulmonary angiography as “gold standard”standard”

Sensitivity for PE is:Sensitivity for PE is:

• 97%97%

• 93%93%

• 87%87%

Question 2Question 2

Accuracy of V/Q scan in PIOPED – incorrect Accuracy of V/Q scan in PIOPED – incorrect

answer?answer?

• 98% sensitivity 98% sensitivity

• 10% specificity10% specificity

• High-probability V/Q scans as PE criteria: High-probability V/Q scans as PE criteria: Failed to detect PE in 59% of patientsFailed to detect PE in 59% of patients

• 70% specificity70% specificity

Question 3Question 3

Accuracy of multiple slice CTA – Accuracy of multiple slice CTA – incorrect answer?incorrect answer?

• Variable sensitivities from 53% to Variable sensitivities from 53% to 87% in different studies87% in different studies

• Reader’s experience is importantReader’s experience is important

• Specificity > 90%Specificity > 90%

• Sensitivity is higher than specificitySensitivity is higher than specificity

Question 4Question 4

Diagnostic accuracy of CTA – incorrect Diagnostic accuracy of CTA – incorrect answer?answer?

• Dependent on clinical probability for Dependent on clinical probability for PEPE

• CTA has high NPV similar to that at CTA has high NPV similar to that at V/Q scanV/Q scan

• Independent from clinical probability Independent from clinical probability for PEfor PE

Diagnostic Pathways in Acute Pulmonary Diagnostic Pathways in Acute Pulmonary EmbolismEmbolism

Recommendations of The PIOPED II Recommendations of The PIOPED II InvestigatorsInvestigators

Diagnostic Pathways in Acute Pulmonary Embolism

Pre Imaging Objective Pre Imaging Objective clinical probability clinical probability • Three clinical scoring system have been tested prospectively and Three clinical scoring system have been tested prospectively and

validated in large scale clinical trials:validated in large scale clinical trials:

Wells’ score Wells’ score (Ann Intern Med 1998)(Ann Intern Med 1998)

Geneva Score Geneva Score (Arch Intern Med 2001, Ann Intern Med 2006)(Arch Intern Med 2001, Ann Intern Med 2006)

Pisa Score Pisa Score (Ann Respir Crit Care Med 1999, Ann j Med (Ann Respir Crit Care Med 1999, Ann j Med 2003)2003)

The diagnostic yield of D-Dimer is lower in cancer patient, the elderly, inpatient, recent trauma or surgery and during pregnancy

CHEST X- RayCHEST X- Ray

• Initial CXR usually normal.Initial CXR usually normal.

• May progress to show atelectasis, May progress to show atelectasis, plueral effusion and elevated plueral effusion and elevated hemidiaphram.hemidiaphram.

• Hampton’s hump and Westermark Hampton’s hump and Westermark signs are classic findings but are not signs are classic findings but are not usually present.usually present.

• Hampton’s Hump Hampton’s Hump – consists – consists of a pleura based shallow of a pleura based shallow wedge-shaped consolidation wedge-shaped consolidation in the lung periphery with in the lung periphery with the base against the pleural the base against the pleural surface.surface.

• Westermark signWestermark sign – – Dilatation of pulmonary Dilatation of pulmonary vessels proximal to vessels proximal to embolism along with embolism along with collapse of distal vessels, collapse of distal vessels, often with a sharp cut off.often with a sharp cut off.

Lung V/Q scanLung V/Q scan• Should lung scan be omitted for pulmonary embolism diagnosis in the age of multislice spiral CT? Should lung scan be omitted for pulmonary embolism diagnosis in the age of multislice spiral CT?

A) YES B) NO A) YES B) NO

NO, Lung scan has a role in PE diagnosis When there are:

Contraindications to CT Scan: Allergy to iodinated contrast agent

Renal failure

Pregnancy?

High diagnostic yield and avoidance of unnecessary radiation exposure. Pregnancy

Young patient with normal X-ray.

Interpretation Criteria of V/Q Interpretation Criteria of V/Q scanscan- P- Prospective rospective IInvestigation of nvestigation of PPulmonary ulmonary EEmbolism mbolism DDiagnosis (iagnosis (PIOPEDPIOPED),), 1990 1990

- Revised PIOPEDRevised PIOPED, 1995, 1995

- PISA-PEDPISA-PED, 1996: Perfusion scan only, 1996: Perfusion scan only

- PIOPED II PIOPED II , 2006, 2006

- Modified PIOPED II : perfusion and CXRModified PIOPED II : perfusion and CXR

PIOPEDPIOPED

• 933/1,493 patients analyzed933/1,493 patients analyzed

• 755 of these patients with pulmonary angiography 755 of these patients with pulmonary angiography within 12– 24 h of V/Q scanwithin 12– 24 h of V/Q scan

• Posterior xenon-133 ventilation scan, followed by an Posterior xenon-133 ventilation scan, followed by an 8-view Tc-99m MAA perfusion lung scan8-view Tc-99m MAA perfusion lung scan

• One-year follow-up: New PE, major bleeding One-year follow-up: New PE, major bleeding complications, or deathcomplications, or death

11Value of the ventilation/perfusion scan in acute pulmonary embolism. Results of the ProspectiveValue of the ventilation/perfusion scan in acute pulmonary embolism. Results of the ProspectiveInvestigation of Pulmonary Embolism Diagnosis (PIOPED). The PIOPED Investigators. JAMA 1990;Investigation of Pulmonary Embolism Diagnosis (PIOPED). The PIOPED Investigators. JAMA 1990;263:2753-9 263:2753-9 

PIOPED: Probability of PEPIOPED: Probability of PE

V/Q scan accuracy: V/Q scan accuracy: PIOPEDPIOPED• Based on PA: 98% sensitivity and Based on PA: 98% sensitivity and

10% specificity for V/Q scan10% specificity for V/Q scan

• High-probability V/Q scans (V/Q High-probability V/Q scans (V/Q mismatch) as criteria for PE: Failed mismatch) as criteria for PE: Failed to detect PE in 59% of patients, to detect PE in 59% of patients, based on PA.based on PA.

Likelihood of PE: PIOPEDLikelihood of PE: PIOPED

Predictive values > 90%: Only 22% of patients. Combined V/Q scan and clinical probability: Highest diagnostic accuracy.High clinical probability & high-probability V/Q scan: 95% likelihood of PE. Low clinical probability & low-probability V/Q scan: 4% likelihood of PE.

PISA-PEDPISA-PED, 1996: Perfusion scan , 1996: Perfusion scan onlyonly

• 890 patients with Q scan, compared 890 patients with Q scan, compared with PAwith PA

• 413/670 (62%) patients with 413/670 (62%) patients with abnormal Q scans had PA; no PA if abnormal Q scans had PA; no PA if normal/near normal Q scannormal/near normal Q scan

• 92% sensitivity and 87% specificity92% sensitivity and 87% specificity

• Positive Q scan and high clinical Positive Q scan and high clinical suspicion: PPV >90%suspicion: PPV >90%

• Negative Q scan and low clinical Negative Q scan and low clinical suspicion: NPV of 97%.suspicion: NPV of 97%.

Normal No perfusion defects of any kind

Near normal Perfusion defects smaller or equal in size and shape to the following roentgenographic abnormalities: cardiomegaly, enlarged aorta, hila and mediastinum, elevated diaphragm, blunting of the costophrenic angle, pleural thickening, intrafissural collection of liquid.

Abnormal compatible with

pulmonary embolism (PE+)

Single or multiple wedge-shaped perfusion defects with or without matching chest-roentgenographic adnormalities. Wedge-shaped areas of overperfusion usually coexist.

Abnormal not compatible with

pulmonary embolism (PE-)

Single or multiple perfusion defects other than wedge-shaped with or without matching chest-roentgenographic abnormalities. Wedge-shaped areas of overperfusion are usually not seen.

Pisa Ped perfusion scan categories and interpretation criteria

Miniati M, et al: Value of perfusion lung scan in the diagnosis of pulmonary embolism: Results of the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISA-PED). Am J Respir Crit Care Med 1996;154:1387–1393.

PISA-PED: ConclusionPISA-PED: Conclusion

• Q scanning alone: Much closer to Q scanning alone: Much closer to angiography than V/Q scanning angiography than V/Q scanning

• Q scanning rather than V/Q scanning: Q scanning rather than V/Q scanning: Imaging technique of first choice for Imaging technique of first choice for diagnosis of PEdiagnosis of PE

PIOPED II: V/Q scan PIOPED II: V/Q scan results results • PE present or PE absent: 74% PE present or PE absent: 74% (PISA-PED: (PISA-PED:

75%)75%)

• Sensitivity for PE present: 77% Sensitivity for PE present: 77% (CTA: (CTA: 83%)83%)

• Specificity of PE absent: 98% Specificity of PE absent: 98% (CTA: 98%)(CTA: 98%)

Conclusions:Conclusions:

V/Q scan provides definitive diagnosis in V/Q scan provides definitive diagnosis in a majority of patients (74%)a majority of patients (74%)

Sostman HD, et al. Acute pulmonary embolism: sensitivity and specificity of Sostman HD, et al. Acute pulmonary embolism: sensitivity and specificity of ventilation perfusion scintigraphy in PIOPED II study. Radiology 2008; 246: ventilation perfusion scintigraphy in PIOPED II study. Radiology 2008; 246: 941-946941-946

Causes of perfusion defects

Primary vascular lesions: Mismatch Q/V Pulmonary thrombpembolism Septic, fat and air emboli PA hypoplesia or atresia Vasculitis

Primary ventilation Abnormality Pneumonia Atelectasis pulmonary edema Asthma COPD, Emphysema, Chronic bronchitis Bullae

Mass Effect: Tumor Adenopathy Mismatch Q/V Pleural effusion

Iatrogenic Surgery: pneumonectomy, lobectomy Radiation fibrosis: Mismatch Q/V

Causes of Nonsegmental perfusion defects

Pacemaker artifactTumorsPleural effusionTraumaHemorrhageBullaeCardiomegalyHilar adenopathyAtelectasisPneumoniaAortic ectasia or aneurysm

Stripe SignStripe Sign: : A thin line A thin line (stripe) of activity between (stripe) of activity between a Q defect and adjacent a Q defect and adjacent pleural surface: sometime pleural surface: sometime in emphysema. Only 6% in emphysema. Only 6% prevalence of PE.prevalence of PE.

Triple matchTriple match: : Matching Q Matching Q and V defect, and CXR and V defect, and CXR abnormality, regardless of abnormality, regardless of size: Atelectasis, size: Atelectasis, consolidation. Prevalence of consolidation. Prevalence of PE: 26% (upper - 11%; PE: 26% (upper - 11%; middle - 12%; lower - 33%)middle - 12%; lower - 33%)11

Focal Hot Spots on Perfusion ScanFocal Hot Spots on Perfusion Scan

A 63 year-old man with a history of diabetes mellitus, who presents with gradual SOB during the 72 hours prior to admission. CXR: No evidence of acute disease. No pleural effusions or infiltrate identified

High likelihood ratio for pulmonary embolism (80-100%)

• This is a 68 year-old man with chest pain undergoing evaluation for This is a 68 year-old man with chest pain undergoing evaluation for pulmonary embolism. The chest radiograph was normal pulmonary embolism. The chest radiograph was normal

Quantum mottle artifact High likelihood ratio for PE

• Elderly woman Elderly woman who presented who presented with sudden onset with sudden onset of tachypnea, of tachypnea, decreased oxygen decreased oxygen saturation, and saturation, and decreased blood decreased blood pressure. pressure.

• The ventilation The ventilation study and CXR are study and CXR are normalnormal

massive pulmonary embolism

V/Q scan: Intermed. probability (20-V/Q scan: Intermed. probability (20-79%)79%)

Single large segmental Q defect in the superior lingular

segment, LUL

V/Q scan: Low probability (10-V/Q scan: Low probability (10-19%)19%)

Patient with SOB. Normal chest x-ray. Markedly heterogeneous

ventilation with central deposition of aerosolized Tc-DTPA

(COPD). Matching V/Q pattern.

Malfunctioning photomultiplier Malfunctioning photomultiplier tube tube

Follow-up V/Q scanFollow-up V/Q scan

• Perfusion pattern changes: Within a few days Perfusion pattern changes: Within a few days after PE after PE

• Large clots may fragment: New peripheral defects Large clots may fragment: New peripheral defects

• Resolution of Q defect: Age dependentResolution of Q defect: Age dependent

• ~15% of patients: Persistent Q defect at one year ~15% of patients: Persistent Q defect at one year

• V/Q scan at 5 to 10 days post PE: marked V/Q scan at 5 to 10 days post PE: marked decrease of Q defects (elderly: 50% decrease at 2 decrease of Q defects (elderly: 50% decrease at 2 weeks) weeks)

CTA:CTA: Advantages and Advantages and limitationslimitations

Initial reports on CTA: Sensitivity for PE of 98%. But sensitivity decreased to 53% to 87% in subsequent studies: Variability due to readers’ experience and image quality.Specificity of CTA has been more consistent: > 90%

Example: CTAExample: CTA

When to use CTA or V/Q When to use CTA or V/Q scanning?scanning?

Clinicians need to consider:Clinicians need to consider:• Institution's experience, particularly for CTA, variable Institution's experience, particularly for CTA, variable

predictive valuespredictive values• Pretest probability of PE (Wells criteria: < 4, PE unlikely; > 4, Pretest probability of PE (Wells criteria: < 4, PE unlikely; > 4,

PE likely)PE likely)• Age and gender of the patient Age and gender of the patient • Renal failureRenal failure• Contrast media allergyContrast media allergy

CTA preferred:CTA preferred:• Experienced CTA readingExperienced CTA reading• High clinical suspicion for PE High clinical suspicion for PE • Clinical suspicion for parenchymal lung diseaseClinical suspicion for parenchymal lung disease

When to use CTA or V/Q scanning?When to use CTA or V/Q scanning?

V/Q as alternative: V/Q as alternative:

• Inexperienced CTA readingInexperienced CTA reading

• Inconclusive CTA but high clinical suspicion for PEInconclusive CTA but high clinical suspicion for PE

• Contraindications for CTA (renal failure, contrast Contraindications for CTA (renal failure, contrast allergy) allergy)

• To minimize radiation dose to patient, particularly To minimize radiation dose to patient, particularly in women of young agein women of young age

• In young patient with normal CXRIn young patient with normal CXR

When to use CTA or V/Q scanning?When to use CTA or V/Q scanning?

Contrast CT of chest 5-8

V/Q SPECTV/Q SPECT

V/Q SPECT (tomographic imaging): Higher accuracy V/Q SPECT (tomographic imaging): Higher accuracy than planar V/Q than planar V/Q • Subsegmental Q defects: Sensitivity increases by 21Subsegmental Q defects: Sensitivity increases by 21%1%1

• Increase of sensitivity, specificity, and observer agreementIncrease of sensitivity, specificity, and observer agreement• Intermediate or inconclusive results < 5%Intermediate or inconclusive results < 5%

11Reinartz P, Schirp U, Zimny M, et al: Optimizing ventilation-perfusion lung scintigraphy: Parting with Reinartz P, Schirp U, Zimny M, et al: Optimizing ventilation-perfusion lung scintigraphy: Parting with planar imaging. Nuklearmedizin 2001;40:38–43planar imaging. Nuklearmedizin 2001;40:38–43Reinartz P, et al. Tomographic imaging in the diagnosis of pulmonary embolism: a comparison Reinartz P, et al. Tomographic imaging in the diagnosis of pulmonary embolism: a comparison between V/Q lung scintigraphy in SPECT technique and multislice spiral CT. J Nucl Med. between V/Q lung scintigraphy in SPECT technique and multislice spiral CT. J Nucl Med. 2004;45:1501–1508.2004;45:1501–1508.Bajc M, et al. Diagnostic evaluation of planar and tomographic ventilation/perfusion lung images in Bajc M, et al. Diagnostic evaluation of planar and tomographic ventilation/perfusion lung images in patients with suspected pulmonary emboli. Clin Physiol Funct Imaging. 2004;24:249–256.patients with suspected pulmonary emboli. Clin Physiol Funct Imaging. 2004;24:249–256.Collart JP, et al. Collart JP, et al. Is a lung perfusion scan obtained by using single photon emission computed Is a lung perfusion scan obtained by using single photon emission computed tomography able to improve the radionuclide diagnosis of pulmonary embolism? Nucl Med Commun. tomography able to improve the radionuclide diagnosis of pulmonary embolism? Nucl Med Commun. 2002;23:1107–1113.2002;23:1107–1113.Leblanc M, et al. Prospective evaluation of the negative predictive value of V/Q SPECT using 99mTc-Leblanc M, et al. Prospective evaluation of the negative predictive value of V/Q SPECT using 99mTc-Technegas. Nucl Med Commun. 2007;28:667–672Technegas. Nucl Med Commun. 2007;28:667–672

V/Q SPECT vs. CTAV/Q SPECT vs. CTA

• 83 patients with suspected PE83 patients with suspected PE

• 97% sensitivity for SPECT and 86% for 97% sensitivity for SPECT and 86% for CTPA CTPA

• SPECT V/Q scan as good as CTASPECT V/Q scan as good as CTA

• Reinartz P, et al. Tomographic imaging in the diagnosis of pulmonary Reinartz P, et al. Tomographic imaging in the diagnosis of pulmonary embolism: a comparison between V/Q lung scintigraphy in SPECT technique embolism: a comparison between V/Q lung scintigraphy in SPECT technique and multislice spiral CT. J Nucl Med. 2004;45:1501–1508.and multislice spiral CT. J Nucl Med. 2004;45:1501–1508.

Example: V/Q SPECTExample: V/Q SPECT

Segmental V/Q mismatch in LLL, subsegmental V/Q mismatch in RML and RLL.Reinartz P, et al. J Nucl Med. 2004;45:1501–1508.

Example: V/Q SPECTExample: V/Q SPECT

Subsegmental V/Q mismatch in RML, segmental V/Q mismatch in LLL.Reinartz P, et al. J Nucl Med. 2004;45:1501–1508.

SPECT/CT - current SPECT/CT - current statusstatusV/Q SPECT and low-dose, non-V/Q SPECT and low-dose, non-

contrast CTcontrast CT• Combined functional and anatomical Combined functional and anatomical

imagingimaging• Same broad indication as for CT Same broad indication as for CT • Contrast media not needed for CTContrast media not needed for CT• Accuracy for PE: Probably at least Accuracy for PE: Probably at least

equivalent to CTAequivalent to CTA• Less radiation exposureLess radiation exposure• No concern for contrast media allergyNo concern for contrast media allergy• Ventilation not be needed (PISA-PED Ventilation not be needed (PISA-PED

trial) trial)

RIGHT TO LEFT RIGHT TO LEFT SHUNTSHUNT

Total Right to Left Shunt from SVC to the Left atrium

Quantitative Lung Quantitative Lung ScintigraphyScintigraphy

Preoperative Lung Preoperative Lung ScintigraphyScintigraphy

Rt. pulmonary A Rt. pulmonary A StenosisStenosis

Pulmonary hypertension-chronic thromboembolic Pulmonary hypertension-chronic thromboembolic DiseasesDiseases

Post-transplant Post-transplant Lung Lung ScintigraphyScintigraphy

• Relative perfusion (RP) of transplanted lung and Relative perfusion (RP) of transplanted lung and FEVFEV11 values during 164 wk of follow-up (A) and perfusion  values during 164 wk of follow-up (A) and perfusion images at 164 wk (B) for patient with chronic rejection. images at 164 wk (B) for patient with chronic rejection.

A

Question 1Question 1

Pulmonary angiography as “gold Pulmonary angiography as “gold standard”standard”

Sensitivity for PE is:Sensitivity for PE is:

• 97%97%

• 93%93%

• 87%87%

Question 2Question 2

Accuracy of V/Q scan in PIOPED – incorrect Accuracy of V/Q scan in PIOPED – incorrect

answer?answer?

• 98% sensitivity 98% sensitivity

• 10% specificity10% specificity

• High-probability V/Q scans as PE criteria: High-probability V/Q scans as PE criteria: Failed to detect PE in 59% of patientsFailed to detect PE in 59% of patients

• 70% specificity70% specificity

Question 3Question 3

Accuracy of multiple slice CTA – Accuracy of multiple slice CTA – incorrect answer?incorrect answer?

• Variable sensitivities from 53% to Variable sensitivities from 53% to 87% in different studies87% in different studies

• Reader’s experience is importantReader’s experience is important

• Specificity > 90%Specificity > 90%

• Sensitivity is higher than specificitySensitivity is higher than specificity

Question 4Question 4

Diagnostic accuracy of CTA – incorrect Diagnostic accuracy of CTA – incorrect answer?answer?

• Dependent from clinical probability for Dependent from clinical probability for PEPE

• CTA has high NPV similar to that at CTA has high NPV similar to that at V/Q scanV/Q scan

• Independent from clinical probability Independent from clinical probability for PE for PE