Ventilation Lung Imaging: Technegas
===================================

* Mary Beth Farrell
* Kathy S. Thomas
* Eleanor S. Mantel
* Jessica Settle

## RATIONALE

Ventilation lung imaging is performed to evaluate lung function related to bronchopulmonary air distribution into and out of the lungs. Technegas (Cyclomedica Asia Pacific) is a system for producing 99mTc-based ventilation studies using a carbon-based nanoparticle. Technegas is not a gas and does not produce aerosolized particles.

## CLINICAL INDICATIONS

*   Detection of pulmonary embolism and recurrent pulmonary embolism.

*   Documentation of pulmonary embolism resolution.

*   Evaluation of quantitative lung function (i.e., lung cancer).

*   Evaluation of lung transplants.

*   Evaluation of congenital heart defects or lung diseases such as the following: 
    
    *   ○ Cardiac shunts.
    
    *   ○ Pulmonary arterial stenosis.
    
    *   ○ Arteriovenous fistula.

*   Confirmation of bronchopleural fistula.

*   Evaluation of chronic pulmonary parenchymal disorders such as cystic fibrosis.

*   Evaluation of pulmonary hypertension.

## CONTRAINDICATIONS

*   Pregnancy must be excluded according to local institutional policy. If the patient is breastfeeding, appropriate radiation safety instructions should be provided.

*   Recent nuclear medicine study (radiopharmaceutical-dependent).

## PATIENT PREPARATION/EDUCATION

*   The patient may eat and take medications as necessary before the procedure.

*   Chest radiography in both the posterior–anterior and the lateral projections or chest CT, ideally performed within 4 h of the scan (acceptable ≤24 h before the scan or since a recent change in clinical status), is required to correlate with the lung scan. An anterior portable chest radiograph is acceptable when a standard chest radiograph is not possible.

*   A focused history containing the following elements should be obtained: 
    
    *   ○ Signs and symptoms (e.g., shortness of breath, chest pain, fever, cough, syncope, tachycardia, jugular venous distention, or hemoptysis).
    
    *   ○ Relevant history, including known diagnoses (e.g., recent surgery, cancer, chronic obstructive pulmonary disease, immobility, or obesity).
    
    *   ○ Results of D-dimer test if ordered.
    
    *   ○ History of prior deep venous thrombosis or pulmonary embolism.
    
    *   ○ Results of images of prior lung scans.
    
    *   ○ Pertinent findings on radiography of the chest.
    
    *   ○ Treatment with anticoagulant or thrombolytic therapy.
    
    *   ○ Results of tests for deep venous thrombosis and other imaging procedures.

*   Educating, and practicing the procedure with, the patient before inhalation of the Technegas is critical to procedure success. 
    
    *   ○ The practice session should be done under the same conditions as the actual ventilation procedure, including position (upright or supine) and using the nose clip.
    
    *   ○ The practice session improves timing, ventilation, and patient compliance (especially with the seal) and offers the opportunity to select the appropriate mouthpiece for that patient.

## RADIOPHARMACEUTICAL IDENTITY, DOSE, AND ROUTE OF ADMINISTRATION

*   The radiopharmaceutical identity, dose, and route of administration are described in Table 1.

View this table:
[TABLE 1.](http://tech.snmjournals.org/content/53/1/11/T1)

TABLE 1. 
Radiopharmaceutical Identity, Dose, and Route of Administration

## PROTOCOL/ACQUISITION INSTRUCTIONS

*   The acquisition parameters for planar imaging and for SPECT or SPECT/CT can be found in Tables 2 and 3, respectively.

View this table:
[TABLE 2.](http://tech.snmjournals.org/content/53/1/11/T2)

TABLE 2. 
Acquisition Parameters: Planar

View this table:
[TABLE 3.](http://tech.snmjournals.org/content/53/1/11/T3)

TABLE 3. 
Acquisition Parameters: SPECT or SPECT/CT

### System Preparation

*   Connect and turn on the argon supply flow rate to 15 L/min.

*   Connect to the main power supply, and switch on.

*   Press the “open” button to open the chamber.

### Crucible Preparation

*   Using gloves and forceps, clear debris from the chamber and ash tray.

*   Wet the well of a new crucible with ethanol and drain, but do not allow it to dry.

*   Use forceps to place the crucible between the chamber contacts, and ensure good contact by rotating forward and backward. Take care not to twist or fracture the crucible.

*   Add 200–900 MBq of 99mTc-pertechnetate in 0.13–0.17 mL with the well vertical, but do not overfill the crucible.

*   Depress and hold the draw interlock and the close button until the chamber is completely closed.

### Simmer

*   Press the start button to initiate the 15-s burn.

*   Verify the burn, and then disconnect the main and argon.

*   Transport the Technegas generator to the patient.

*   Administer the Technegas within a 10-min window.

### Patient Ventilation

*   Attach the patient administration set to the Technegas generator.

*   Commence the practiced breathing strategy with the patient.

*   Press the start button.

*   On inspiration, depress the patient delivery knob.

*   Monitor the lung count rate.

*   When a rate of 1,500–2,500 counts/s in the posterior position is achieved, release the delivery knob and allow the patient to take 1–3 breaths through the tube to clear the residual.

*   Dispose of the patient administration set.

*   Return the Technegas generator to argon and main power supply, which will automatically commence a purge.

### Ventilation Imaging

*   Begin imaging immediately after completion of the delivery of the radioactive aerosol.

*   Acquire planar images in multiple projections, to include anterior, right anterior oblique, right lateral, right posterior oblique, posterior, left posterior oblique, left lateral, and left anterior oblique.

*   SPECT imaging is optional. Position the patient supine on the imaging table with arms above head and out of the field of view. Set the camera to acquire a SPECT scan of the chest region such that the entire lung is in the field of view.

### Common Options

*   CT may be performed with the SPECT camera and can be low-dose, nondiagnostic CT for attenuation correction, diagnostic CT, or a CT pulmonary angiogram.

## IMAGING PROCESSING

*   Planar images should be scaled to visualize areas of uptake or absence of tracer.

*   SPECT images should be processed per the manufacturer’s recommendation and the interpreting physician’s preference, including preprocessing, reconstruction (transverse, sagittal, and coronal views), filter selection, and image display.

*   Iterative reconstruction is recommended.

*   If SPECT/CT is performed, images can be fused for attenuation correction and correlative interpretation.

*   For SPECT/CT protocols, refer to the manufacturer’s recommendations for CT acquisition parameters.

*   For quantitative ventilation lung scans: 
    
    *   ○ Place regions of interest over the right and left lungs in both the anterior and posterior projections.
    
    *   ○ Divide each lung into 3 equal rectangular regions of interest on the anterior and posterior views: top, middle, and bottom. The division of the lungs into thirds does not exactly correlate with the anatomic divisions of the lung lobes but is reasonably representative.
    
    *   ○ Determine the total activity for each lung in addition to the activity in all 6 regions of interest.
    
    *   ○ Calculate the geometric mean: the square root of the product of the anterior counts multiplied by the posterior counts (√ [anterior counts × posterior counts]) for all lung regions. The geometric mean is used because it is more representative than the arithmetic mean ([anterior counts + posterior counts]/2).
    
    *   ○ Calculate the percentage of counts in each region.

## ADJUNCT IMAGING/INTERVENTIONS

*   Bronchodilator therapy can improve study accuracy in patients with acute obstructive lung disease.

## Footnotes

*   * Reprinted from Farrell MB, Thomas KS, Mantel ES, Settle J. *Quick-Reference Protocol Manual for Nuclear Medicine Technologists*, 2nd ed. Society of Nuclear Medicine and Molecular Imaging–Technologist Section. 2024:397–401.

## REFERENCES

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*   Received for publication January 17, 2025.
*   Accepted for publication January 17, 2025.