lung scan & radionuclide venography for md4-ns students_2017

Nuclear Medicine Studies for MD4_NS

Jiraporn Sriprapaporn, M.D.

Division of Nuclear Medicine

Department of Radiology

Siriraj Hospital 16 February 2017

Nuclear Oncology

Lung Scan & RNV

Lung Scan: - Ventilation (V) & Perfusion (Q)

Indications : Diagnosis of pulmonary embolism

Radiotracers :

Ventilation (V) lung scan : Xe-133, Tc-99m DTPA aerosol, Technegas

Perfusion (Q) scan :Tc-99m MAA

Patient preparation : None

Lung scan

By Jiraporn Sriprapaporn

Mechanism

Ventilation lung scan: Compartmental localization

Perfusion lung scan: capillary blockage 1/1000

The biologic half-life of the MAA in the lungs is about 1.5–3 hrs.

Principles of V/Q Lung Scan


Injection of Tc-99m MAA in supine position

Static imaging 6-8 views +/- SPECT/CT

Perfusion Lung Scan


PE Segmental perfusion defects

Defect size // size of clot, location of occlusion

PE: Pathophysiology


Bronchopulmonary Segments


O2

Radioaerosol Ventilation Scan


Tc-99m DTPA Radioaerosol Ventilation Scan


Technegas


Technegas Ventilation Scan


NORMAL:

Uniform distribution of the radioactivity

ABNORMAL”

Non-uniform distribution

Defects

Size: small (< 25%), medium (25-75%), large (>75%)

Number

Pattern: Segmental (// bronchopulmonary segments) or non-segmental defects.

Interpretation of V/Q Lung Scan

V+ Q + CXR within 24 hrs.


A: Ventilation

B: Perfusion

Normal V/Q Lung Scan


V/Q match: parenchymal or airway diseases

V/Q mismatch: vascular occlusion (pulmonary embolism)

Findings


Comparison of V/Q Scan and Pulmonary CTA

V/Q Lung Scan

• Advantages

• High NPV in patient with low pretest prob.

• High PPV in patient with high pretest prob.

• Safe, no contrast reaction

• Lower radiation- good for F/U

• Disadvantages

• Limited available

• Longer exam time

• Needs Pt. cooperation (V)

• Cannot provide alternative diagnosis

Pulmonary CTA

Advantages

More available, 24 hrs

Short exam time – better for unstable patient

Clearly identify clots

Can provide alternative diagnosis

Disadvantages

Higher radiation*

Possible contrast allergy

Possible nephrotoxic

CTPA: Males = 9.7 mSv, Females = 8.4 mSv [Woo Jk 2012] Q scan (4 mCi) = 1.5 mSv [SNM]


Can evaluate perfusion defects from PE and

Can diagnose DVT (source of emboli) in the same

setting - by radionuclide venography (RNV) (RNV must be initially requested)

Unique advantage of Q lung scan


Ventilation, Perfusion, and Radiographic Interpretive Criteria for PE

(SNM guideline v4, 2012)

PIOPED Modified PIOPED II

High LR [> 80% risk]

- >2 large mismatched (V:Q)

segmental defects*

High LR [85-90% risk]

- > 2 large mismatched (V:Q) segmental defects*

Borderline high LR

- 2 large mismatched (V:Q)

segmental defects*

Intermediate LR [20-80% risk]

- 2 moderate or 1 large mismatched

(V:Q) defect*

- Difficult to categorize as high or low

Nondiagnostic [20-80% risk]

- All other findings

Borderline low LR

- 1 matched (V:Q) defect, CXR-negative

Low LR [< 20% risk]

- Nonsegmental perfusion defects†

- Q defect substantially < CXR defect

- Matched (V:Q) defects, CXR-negative

- Any number of small Q defects*

Very low LR [< 10 % risk]

- Nonsegmental†

- Q defect < CXR lesion

- 1–3 small segmental*defects

- Solitary matched (V:Q:CXR) defect (#1 segment) in mid

or upper lung

- Stripe sign‡

- Solitary large pleural effusion§

- > 2 matched (V:Q) defects, regionally normal CXR

Normal

- No Q defects

Normal

- No Q defects

*Or equivalent where large segmental defect, >75% of segment, equals 1 segmental equivalent; moderate defect, 25%–75% of segment, equals 0.5 segmental equivalent; small defect, < 25%, is not counted.


Modified PIOPED II criteria reported as probability

or likelihood ratio for presence of PE

High prob. : PPV > 85%, ≥ 2 large V/Q mismatched segmental perfusion defects

Non-diagnostic

Very low prob. : PPV < 10%

Normal : Significant PE is excluded.

Interpretation of V/Q Lung Scan: Modified PIOPED II criteria


V/Q Lung Scan Classification

High Prob

Nondiagnostic

Very low prob

Normal


Pulmonary Embolism: Before & After Anticoagulant Rx


Ascending Radionuclide Venography (RNV): Techniques

Radiopharm: Tc-99m phytate/ sulfur colloid, Tc-99m MAA* (+ Q lung scan)

Inject a tracer via (bilateral) foot veins

On tourniquets above ankles to visualize deep veins and off tourniquets for superficial veins


Ascending RNV: Interpretation

Bilateral comparison, on & off TQ

Normal: Good flow without signs of venous occlusion

Abnormal: Obliteration of flow, filling defect, asymmetric flow +/-collaterals


Normal Asc RNV

Whole-body Images

phytate

Multiple Static Images


Normal vs Abnormal RNV


DVT WITH PE


Accuracy of Asc RNV

Authors Year No. (studies)

Sen (%)

Spec (%)

Corr (%)

Site of DVT

Webber (12) 1974 30 65 92 77 Overall Henkin (13) 1974 25 100 86 96 Proximal Van Kirk (14) 1976 19 100 95 95 Overall Vlahos (15) 1976 52 100 100 100 Pelvis 98 89 100 97 Thigh 98 92 97 95 Calf Ennis (16) 1977 154 90 89 95 Overall

Cordoba (17) 1977 44 100 80 94 Overall Ryo (18) 1977 47 89 66 89 Overall Gomes (19) 1982 51 88 65 67 Overall Mohamadiyeh(20) 1993 32 90 73 89 Proximal

Mangkharak 1998 72 88 96 90 Overall 55 95 97 96 Pelvic 72 95 100 90 Thigh 72 77 96 83 Calf

Mangkharak J, et al. J Med Assoc Thai 1998;81:432-441

Acute Pulmonary Embolism

Perfusion-Ventilation lung scan ***

Multiple segmental V/Q mismatched defects , no

radiographic abnormality

Increasing no. of defects increasing specificity

Pulmonary angiography is the original gold

standard, now usually being replaced with CTPA.

V/Q scan cannot DDx acute from chronic PE, so

F/U scan to evaluate the lung status post Rx *** (Baseline for the new episode, if any)


V/Q Lung Scan for Dx PE

Advantages

• Simple, noninvasive, safe, and economical

• High specificity (98%) esp. increasing no. of defects

• The usefulness is well documented.

• Can evaluate the cause -DVT in the same setting.

Disadvantages

Not widely available

Minimal radiation

Low sensitivity (41%)

Limitation in abn CXR

V/Q scan cannot DDx acute from chronic PE need F/U

scan


Management Guideline

Normal Rule out clinically significant PE

Very-low probability Find out other causes of symptoms.

Nondiagnostic Cannot rule out PE and needs further investigations such as ultrasound for DVT.

High prob The patient can be treated for PE.


High clinical probability Pulmonary CTA followed by

V/Q scan for baseline & F/U

Low clinical probability (normal CXR) V/Q lung scan

Presence of underlying lung disease CTA

Suggestion

Assessment of clinical probability of Pulmonary Embolism (Wells Score) • Symptoms of DVT (3 points) • No alternative diagnosis better explains the illness (3 points) • Tachycardia with pulse > 100 (1.5 points) • Immobilization (>= 3 days) or surgery in the previous 4 wks (1.5

points) • Prior history of DVT or pulmonary embolism (1.5 points) • Presence of hemoptysis (1 point) • Presence of malignancy (1 point)

Score < 2 = Low prob Score 2-6 = Mod. prob Score > 6 = High prob


lung scan & radionuclide venography for md4-ns students_2017

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