Ventilation Lung Imaging: Technegas

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.

PROTOCOL/ACQUISITION INSTRUCTIONS

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

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.