NUCLEAR MEDICINE IN LUNG DISEASES

Prof. Dr. Haluk B. Sayman

Pulmonary embolus (PE) diagnosis is difficult than expected in the clinical settings. Only a few patients show classical symptoms of side pain, dyspnea and hemoptysis.

The etiology consists of deep venous thrombosis . Diagnosis of DVT by USG or venous scintigraphy increases the probability of PE.

Plasma D-dimer test is an important but non-specific indicator. Normal results lowers the probability of PE.

Pulmonary Embolus - Clinics

Lung X-ray: Indistinction (collapse) of vascular bed distal to the embolus (Westermark sign), dilatation of pulmonary arteries proximal to PE (Fleischner sign), a wedge shaped, pleural based consolidation (Hampton’s hump) are not frequent and hard to detect. Pulmonary effusions are usually present. It helps to differentiate PE from pneumothorax, pneumonia or aortic dissection.

Contrast angiography: It is interventional and has morbidity and mortality. Death is infrequent but arrythmias are frequent. Quantitative specifications and thrombolytic therapy potential are advantages. Although gold standart, because of difficulties and danger it is not prefered in clinical setting.

Pulmonary Embolus – Imaging - I

CT Angiography: Rapid and thin tomographic slices are available after introduction of spiral CT. But it is unsuccessful in subsegment emboli and has high radiation risk. Negative results does not exclude PE.

MRI: Blood flow measurement, contrast methods may be used. It has no radiation risk like CT but it is similarly unsuccessful in small subsegmenter emboli.

Pulmonary Embolus – Imaging - II

Ventilation and Perfusion Scintigraphy: Labelled macroaggregated human albumin is used in perfusion scintigraphy and it is trapped in vascular bed by microemboli. 75 MBq Tc-99m MAA, containing 60-500 K particles, is given iv, without mixing with blood in supine position. Alternatively inert gases (e.g. Xe-133) which dissolves in blood and rapidly passing into alveolar space can be used.Inert gases (Xe-133, Kr-81m) or labelled aerosols (Tc-99m DTPA, Tc-99m PYP) are used for ventilation scintigraphy. The most ideal images are obtained by Technegas® which is a dispersion of labelled carbon particles, whereas the optimal agent is Kr-81m.

Pulmonary Embolus – Imaging - IIIa

Normal Lung Perfusion Images

Lung perfusion and ventilation imaging is usually done simultaneously for diagnosis of PE. In PE, while pulmonary perfusion through pulmonary veins is impaired, the lung parenchyme is fed by bronchial arteries and ventilation stays normal. This is named as ‘mismatch’.

Pulmonary Embolus – Imaging - IIIb

Perfusion defects without any matching ventilation defects indicates high probability for PE. There may be subsegmenter, segmenter, lobar or even whole lung defects. Multiple defects increase, subsegmenter defects decrease the probability of PE. COPD, asthma, abcess, tumors, heart-lung disease and atelectasia produce matching defects whereas pneumonia and pleural effusion produce reverse mismatch with more prominent defects in ventilation.

Pulmonary Embolus – Imaging - IIIc

Different criterias are defined for the diagnosis of PE to interpret the lung perfusion and ventilation scintigraphies.◦ Biello◦ PIOPED I-II and III

A perfusion scan with subsegmenter defects, independent from the X-ray and ventilation findings or with matching perfusion defects and abnormal X-ray findings, indicates low probability for PE. Two or more perfusion defects without ventilation and X-ray findings yield high probability for PE diagnosis.

Pulmonary Embolus – Diagnosis I

Normal: No perfusion defects. Practically, normal perfusion scintigraphy eliminates PE probability.

Near Normal: Non-uniform uptake with no definite segmental or subsegmental perfusion defects

Low: ◦ Non-segmental perfusion defects other than cardiomegaly or

other prominent hilar structures◦ Matching V/Q defects without corresponding X-ray

abnormality◦ Any number of only small perfusion defects regardless of

ventilation and X-ray patterns◦ Stripe sign◦ Perfusion defect substantially smaller than X-ray abnormality

Pulmonary Embolus – Diagnosis II

High:◦ Two or more large mismatching defects or equivalent

(4 moderate or 1 large plus 2 moderate defects) without corresponding X-ray abnormalities

◦ Perfusion defect substantially larger than X-ray abnormality

Intermediate:◦ Perfusion defect matching X-ray abnormality with size

and location◦ Single moderate up to less than 2 segmental

mismatching defects without corresponding X-ray abnormality

◦ Those difficult to categorize as low or high

Pulmonary Embolus – Diagnosis III

Pulmonary Emboli

High probability PE

Pulmonary Emboli

Pulmonary Hypertension is presented by chronic thromboembolisms and high and intermediate probability patterns are seen.

Obstructive airways disease is defined by central deposition of radiotracer on ventilation scans.

Remnants after major lung operations must supply at least 700 ml/min FEV1. Postoperative respiratory requirement is predicted by quantiative lung scans. The ratio of the area planned for resection to the whole lung is calculated on lung scan and multiplied by the current FEV1. If this value is higher than minimum required FEV1, then operation is safe.

In lung transplantation lung scans are used for donor selection and postoperative follow-up.

Other Lung Diseases I

Mucociliary clearance of respiratory epithelium is disturbed with cystic fibrosis, primary ciliar dyskinesia, mechanical and chemical irritations, viruses and microps. Time activity curves are used to measure MSC by the clearance of ventilated Tc-99m labelled aerosoles such as SC, MAA, DTPA.

In bronchiectasia, asthma, COPD MSC decreases, on the other hand in smokers first decreases then increases.

The diffusion of aerosols through alveolobasal membrane is measured to complement the diagnosis for AIDS, alveolitis, sarcoidosis and pneumonia.

Other Lung Diseases II

This is a subject of another lecture

Lung tumors

CT PET PET/CT