CT SCAN TECHNIQUE OF CHEST

CT SCAN TECHNIQUE OF CHEST:

 Parameters:

Position/Landmark: Supine head or feet first/from the level of chin
Scout: AP/ Top of chest through kidneys
Scan Type/Direction: HELICAL with single breath hold/ Craniocaudal
Pitch/Mode Speed/Rotation: 1.5/10mm/rotation .6sec/rotation
KVP/mA/Rotation Time: 120/AUTO mA
Slice Thickness / Spacing: 5mm x 5mm
Starting and Ending Locations: Scan approx. 512mm from the level 1 inch below chin through the adrenals or umbilicus
DFOV: Adjust to patient size/ Average is 36-40
Amount / Type Contrast/ Injection Rate: 100 mm Non-ionic monomer 300 mgI/2-3ml/sec
Scan Delay: Start scan when both ascending and descending aorta are lit up (Bolus Tracking may be suitable or keeping scan delay time)
Scanned Phases: Venous phase (Entire Mediastinum bright)
Prospective Recons: Recon 1: Standard 5x5 or 8x8 or 10x10 (w400 x L40)
                                Recon 2: Lung 1.25x5 or 1.25x10 (w1700 x L-500)
                                Recon 3: Soft 1.25 x .75 for  3D, MPR, MIP
Reformats/Post Processing: Average Coronals and Sagittals

Indications:

1. Primary lung cancer (assessment of extent of primary tumor, the relationship of tumor to pleura, chest wall, airways and mediastinum; detection of hilar and mediastinal lymphadenopathy) and staging of metastatic disease (extrathoracic malignancies with propensity to involve the lungs- osteogenic sarcoma, breast, RCC).
2. Evaluation of solitary pulmonary nodule seen on chest x-ray or included on abdominal CT (lymphoma, tumor, great vessel disease-aortic aneurysm or dissection, intramural hematoma, aortitis, and widening on Chest x-ray).
3. Mediastinal pathology (adenopathy, mits, infection; localization and characterization of mediastinal mass).
4. Cardiac and pericardial disease (Tumor, Inflammation and Pericardial Effusion).
5. Pulmonary Infection and inflammatory diseases (consolidation-pneumonia, known disease or to monitor response to therapy e.g. Sarcoid, CVD, Bronchiectasis, Pneumoconiosis, Hypersensitivity Pneumonitis, IPF (Interstitial Pulmonary Fibrosis), COPD, Asbestosis, Cystic Disease, Infection- TB, PCP, MAC etc, Normal CXR with symptoms or abnormal PFT to detect interstitial disease.
6. Trauma
7. Rule out Pulmonary Embolism
8. Lung Cancer Screening
9. Coronary Artery Calcium Detection
10. Distinction of empyema from peripheral lung abscess 

Patient Positioning:

The patient lies supine, head first on the scanner table. Arms are raised and placed behind the patient's head, out of the scan plane. Positioning is aided by transaxial, coronal and sagittal alignment lights. The median sagittal plane is perpendicular and the coronal plane is parallel to the scanner table top. The scan plane is perpendicular to the long axis of the body to enable that the coronal plane alignment light is at the level of the mid-axillary line. The patient is now moved in to the scanner until the scan reference point is at the about 1 inch below the level of chin.

Imaging Procedure:

 A postero-anterior scan projection radiograph is acquired, covering at least C7 upto the the level of adrenals. A posterior-anterior projection is selected to reduce the radiation dose to the thymus and breast tissue. From this scan image, 10 mm contiguous sections are prescribed throught the lung fiedlds and upper abdomen starting at the lung apices and ending just below the costophrenic angles. Scans are acquired during arrested respiration. In suspected bronchial carcinoma, scanning continues through the adrenal glands  check for metastatic spreads.

Filming:

A 5x6 layout is chosen. First scanogram and scanogram with dotted scan lines and non-contrast standard images are send to filming window. Then, the information less images according to the pathology, images of the begining or of the ending can be cut. Images are maximum zoomed to the edges of each box, centered at the middle of the box. Contrast enhanced images are loaded to the filming window. Then the images are maximum zoomed to the edges, centered at the middle of the box. Lung window images are loaded to the filming window. The images covering lung parenchyma may only be useful. So, 4x6 format may be chosen. The images are maximum zoomed to the edges of the box, centered at the middle of the box. Now, thin slice contrast enhanced images are loaded in MPR window. Coronal images are obtained by prescribing the scan lines from the anterior to the posterior lung. About 12 coronal images are send to the filming window. Scan lines are rotated and sagittal images are obtained by prescribing the scan lines from right to left. About 12 sagittal images are send to the filming window. Then, 24 MPR images are printed in 4x6 format. Altogether we printed 4 sheets.