Pulmonary Nuclear Medicine: Techniques and Uses

Overview:

Lung cancer is one of the most severe diseases worldwide. Every year almost 2 million people are diagnosed with lung cancer. It is the second most prevalent cancer in the world. Around 1.6 million people are losing their life to lung cancer. That is why early diagnosis and modern treatment intervention are required in fighting these conditions. Nuclear medicine is one of the newest branches of modern medical science, helping researchers find new ways to cure lung cancer.

What Is Nuclear Medicine?

Nuclear medicine is a medical science branch dealing with radioactive tracer molecules. These molecules are used for diagnosing and treatment purposes. These molecules are helpful in studying cellular functioning and characteristics. Radioactive tracer molecules are made up of radioactive elements and carrier molecules. With the help of the carrier molecules, these tracer molecules traveled to the target organs or bound to the specific cellular compound. These molecules are also called radiopharmaceuticals.

Special types of cameras or sensors are used to map these molecules. As a result, a picture of the organ can be identified, and diseased cells can also be identified. The main role of nuclear medicine is in imaging procedures. Different types of imaging techniques used for this purpose are ventilation and perfusion imaging and positron emission tomography.

What Are the Nuclear Imaging Techniques?

The nuclear imaging techniques are:

1. Ventilation and Perfusion Imaging: This procedure is used in case of suspected case pulmonary embolism. Radiolabeled macro aggregated albumin (MAA) is accessed for this purpose. The other name of this scan is lung scintigraphy or V/Q scan.

• Procedure:

• During the ventilation scan, the patient is asked to inhale radioactive xenon or technetium through a nebulizer via mouthpiece for a few minutes.

• During perfusion scanning, radioactive dye-containing technetium is administered intravenously.

• For ventilation scanning, 99mTc-diethylenetriaminepentaacetic acid (DTPA) is used in the form of an aerosol. The diameter of the aerosol is 4.5 micrometers with a half-life of 6 hours. A maximum dose of 25 to 35 millicuries of this radiopharmaceutical is administrated via nebulizer.

• Inert gases used for ventilation scanning are 133Xe and 81mKr. The maximum dose of such gases is 5- 20 millicuries.

• In perfusion, scintigraphy 9mTc-macro aggregated albumin (99mTc-MMA) with a particle size of 10 to 100 micrometers is injected intravenously with a dose of 40 to 150 mega-becquerel.

• The procedure is done in two phases. At first, the ventilation scaling is done; after that, perfusion scanning is performed.

• The patient is asked to lie on the table and breath normally. Images of the target portion are taken using a gamma camera.

• A wedge-shaped defect can be seen due to the blockage of the arteries.

• Uses:

• Arteriovenous malformations can be detected using perfusion scanning.

• Extension of the cancerous lesions and their accessibility can also be evaluated using perfusion scanning.

• Differentiation between primary and secondary hypertension is possible using perfusion scanning.

• The function of the small airways, pulmonary obstruction, and regional ventilation can be evaluated using ventilation scanning.

• Pulmonary embolism and response to radiotherapy can be evaluated through both ventilation and perfusion scanning.

2. Positron Emission Tomography–Computed Tomography (PET-CT) Scan:

In this type of scanning picture, positron emission tomography (PET) and computed tomography are combined. Different radiographic tracers are used for the assessment of the functioning of lung tissues. The most commonly used tracer used for this purpose is 8F-Fluorodeoxyglucose (FDG). This substance enters cells like glucose enters the cells. The malignant cells have high glucose affinity. That is why higher FDG uptake can be seen in malignant cells.

• Procedure:

• FDG is administered intravenously around 60 to 90 minutes before the procedure.

• The patient is positioned supine on the imaging table.

• A spiral computed tomography is performed in the area of interest.

• Then the PET scanner, which is part of the machine, performs the emission detection from the radioactive molecules. Fluorine-18, present in the FDG, emits positrons. These molecules interact with electors and emit photons. The photons travel exactly in the opposite direction, and these photons are detected by the cameras.

• Many transaxial PET and CT images are reconstructed, and then these images are reformatted into coronal and sagittal images.

• Uses:

• Identification of solitary lung nodules and lung lesions which are less than 3 centimeters in diameter can be identified.

• Cellular metabolic changes can be identified.

• Proper diagnosis of solitary lung nodules, which are bigger in size, can be identified using FDG uptake.

• Accurate staging of f non-small cell lung cancer can be possible.

What Are the Molecules Used in Nuclear Medicine?

Different radioactive molecules are used in nuclear medicine. These substances are used for the purpose of labeling different cells. These molecules include the following:

1. Gallium-67 Citrate: This is one of the most widely used molecules in pulmonary nuclear medicine. Accumulation of these tracers can be seen in various conditions like sarcoidosis and Pneumocystis carinii pneumonia (PCP) in HIV patients and in various granulomatous disorders.

2. Indium-Ill Oxine Labeling of White Blood Cells: White blood cells are labeled using these tracers. These are used to confirm intrapulmonary inflammations.

3. Thallium-201 Chloride: These radioactive tracer molecules can be useful in detecting malignancy. Non-Hodgkin's lymphomas, lymphomas can be detected using these tracers.

4. Technetium-99m Glucoheptonate: These tracers are used to detect the blood flow activity of the neoplasms.

5. Iodine-123-labeled Somatostatin Analogue: Small cell carcinoma of lung cancer can be detected using these tracers. These tracers can be used to label somatostatin receptors which can be useful for the detection of small-cell lung cancer.

6. Indium- 111 Labeled Carcinoembryonic Antigen-Specific Monoclonal Antibodies: Carcinoembryonic antigen is a specific type of glycoprotein that can be seen in lung cancers. Monoclonal antibodies present against such antigens can be identified using these tracers.

Conclusions:

Lung cancer is a fatal disease. Early and accurate detection of lung cancer is difficult. Using modern diagnostic methods, accurate characterization of lung cancers is difficult. With the help of nuclear medicine, proper identification of carcinoma and lung changes can be identified. Also cellular and tissue changes can also be seen at the molecular level. Thus, nuclear medicine has an important role in detecting lung cancer.