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HLT-RADI64-08 · Lesson 2 · 27 clock hours · lab

Advanced Radiographic Positioning: Chest, Abdomen, and Digestive Tract

Objective. Students produce diagnostic-quality phantom images of the chest and abdomen in all standard and supplementary projections, applying correct IR size, SID, centering, and exposure indicators.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Advanced Radiographic Positioning: Chest, Abdomen, and Digestive Tract

Producing diagnostic-quality images of the chest, abdomen, and digestive tract requires precise positioning, appropriate technical factors, and a thorough understanding of anatomy. In this lab you will apply those skills using an anthropomorphic phantom and critique images against established positioning standards.

Chest Projections

The PA chest is the standard projection. The patient stands erect, posterior surface against the IR, with the midsagittal plane centered to the IR. The IR is sized to include the apices and costophrenic angles — typically a 14 × 17 inch (35 × 43 cm) detector placed lengthwise. Source-to-image distance (SID) is 72 inches (183 cm), which reduces cardiac magnification and allows full inspiration. Exposure is taken at the end of a deep breath. Optimal positioning shows both lungs fully expanded, no rotation (medial ends of clavicles equidistant from the spine), and complete visualization of the costophrenic angles.

The lateral chest is taken erect with the left side against the IR to minimize cardiac magnification. The arms are raised clear of the thorax. The same 72-inch SID applies. A properly positioned lateral shows superimposition of the posterior ribs and an open retrosternal space.

The AP lordotic projection is a supplementary view used to demonstrate the lung apices free of clavicular superimposition. The patient leans back approximately 45 degrees against the IR, or the CR is angled 15–20 degrees cephalad in the AP position. This view is not part of the routine series but is ordered when apex pathology is suspected.

The lateral decubitus projection (left or right) is performed with the patient lying on one side on the table or cart, with a horizontal beam directed AP or PA. It demonstrates free fluid (which layers dependently) or free air (which rises to the uppermost side). The entire thorax must be visible, and the image must be taken with the patient perfectly lateral to avoid rotation artifacts.

Abdomen Projections and Acute Abdominal Series

The routine AP abdomen (KUB — kidneys, ureters, bladder) uses a 14 × 17 inch detector placed lengthwise, SID of 40 inches (102 cm), with the patient supine. The CR enters at the level of the iliac crests to center the abdomen on the IR. Both psoas muscles, renal outlines, and the symphysis pubis should be visible.

The acute abdominal series (obstruction series) typically includes the supine AP abdomen, an erect AP abdomen, and an erect PA chest. The erect AP abdomen demonstrates air-fluid levels in bowel obstruction and free intraperitoneal air under the diaphragm. The patient must be erect for at least 5 minutes before exposure so fluid has time to layer. When the patient cannot stand, a left lateral decubitus abdomen is substituted — it detects free air between the right lateral abdominal wall and the liver.

Oblique and lateral abdomen projections are added when the requisition or radiologist requests them for organ-specific evaluation.

Exposure Indicators and Repeat Documentation

Digital radiography systems report an exposure indicator (EI) that reflects the radiation exposure to the detector. The specific scale and target values vary by manufacturer (Fuji, Carestream, Agfa, Siemens each use different naming conventions and numeric ranges), so always consult your department's reference chart. A value within the accepted range indicates appropriate exposure. A significantly high EI means overexposure (excess radiation dose to the patient); a significantly low EI means underexposure (risk of a noisy, non-diagnostic image). Any repeat must be documented with the cause (positioning error, motion, exposure error, equipment issue) and the corrective action taken — this practice is required for radiation safety programs and quality improvement.

Upper GI Series: Contrast Study Workflow

An upper GI (UGI) series uses barium sulfate suspension, or occasionally a water-soluble iodinated contrast agent when perforation is suspected, to opacify the esophagus, stomach, and duodenum under fluoroscopy.

Before the study begins, review the requisition carefully: confirm patient identity, the clinical indication, and whether any contraindications exist. Screen the patient for contrast allergies — barium allergy is rare but documented; iodinated contrast allergy is more significant and requires physician notification and possible premedication. Ask about prior abdominal surgery, suspected perforation (barium is contraindicated if perforation is possible), and ability to swallow. The patient is NPO (nothing by mouth) for several hours before the exam.

Explain the procedure in plain language: the patient will swallow contrast material while positioned on the fluoroscopy table, and the radiologist will take spot images as the contrast moves through the upper GI tract. Positions include erect PA, RAO (right anterior oblique to profile the esophagus and duodenal bulb), LAO, and lateral. The table is often tilted to Trendelenburg to demonstrate reflux when indicated.

When critiquing fluoroscopic spot images, assess: correct anatomy included, adequate coating of mucosa, absence of motion blur, appropriate collimation, and whether the structure of interest (e.g., duodenal bulb, gastroesophageal junction) is centered and free of superimposition.

Safety Reminders

Key terms8

Exposure Indicator (EI)A numeric value reported by a digital radiography system that indicates the level of radiation exposure received by the detector; used to assess whether the selected technical factors were appropriate for the projection.
Source-to-Image Distance (SID)The measured distance from the focal spot of the X-ray tube to the image receptor; standardized distances (commonly 40 inches for general radiography, 72 inches for chest) affect magnification and image sharpness.
AP Lordotic ProjectionA supplementary chest projection in which the patient leans backward or the central ray is angled cephalad, projecting the clavicles above the lung apices to demonstrate apex pathology without bony superimposition.
Lateral DecubitusA projection taken with the patient lying on one side and the X-ray beam directed horizontally; used to demonstrate free air (rises to the uppermost side) or free fluid (layers dependently) in the chest or abdomen.
Acute Abdominal SeriesA set of radiographic projections — typically supine AP abdomen, erect AP abdomen, and erect chest — ordered to evaluate acute abdominal conditions such as bowel obstruction or visceral perforation.
Barium SulfateAn inert, high-atomic-number contrast agent swallowed or instilled to opacify the gastrointestinal tract during fluoroscopic studies; contraindicated when bowel perforation is suspected.
ALARAAs Low As Reasonably Achievable — the guiding radiation protection principle requiring that patient and worker radiation dose be kept as low as possible while still achieving diagnostic image quality.
RAO (Right Anterior Oblique)A patient position in which the right anterior surface of the body is closest to the image receptor; commonly used during upper GI series to profile the esophagus, duodenal bulb, and pylorus.

Worked examples4

1. Your department's EI reference range for a PA chest is 150–250 (manufacturer scale). After exposing the phantom, the DR console displays EI = 420. What does this indicate, and by approximately what factor is the detector overexposed relative to the midpoint of the reference range?
  1. Identify the midpoint of the reference range: (150 + 250) / 2 = 200.
  2. Divide the obtained EI by the midpoint: 420 / 200 = 2.1.
  3. Interpret the result: an EI of 420 is approximately 2.1 times the midpoint reference value, indicating the detector received roughly twice the expected exposure.
  4. Conclude: the image represents patient overexposure. Document the repeat, identify the technical factor error (e.g., mAs too high), reduce mAs or adjust kVp, and re-expose.
Answer: EI 420 is approximately 2.1× the reference midpoint of 200, indicating overexposure. Reduce mAs for the repeat exposure and document the cause and correction.
2. You are setting up for a PA chest. The department protocol requires a 72-inch SID. Your tube is positioned with the focal spot 60 inches from the IR. How many additional inches must you extend the column to reach the correct SID?
  1. Required SID = 72 inches.
  2. Current tube-to-IR distance = 60 inches.
  3. Additional distance needed = 72 − 60 = 12 inches.
Answer: The tube column must be extended 12 more inches to achieve the required 72-inch SID.
3. During an acute abdominal series, the requisition calls for an erect AP abdomen to check for air-fluid levels. The patient has been lying supine. The protocol states the patient must be erect for at least 5 minutes before exposure. You note the patient was stood up only 2 minutes ago. How many additional minutes must you wait, and what is the clinical reason?
  1. Required erect time = 5 minutes.
  2. Time already elapsed = 2 minutes.
  3. Additional wait time = 5 − 2 = 3 minutes.
  4. Clinical reason: free intraperitoneal air and fluid within bowel loops need sufficient time to redistribute under gravity before they can be visualized as distinct air-fluid levels or as free air under the diaphragm.
Answer: Wait an additional 3 minutes (total 5 minutes erect) so that fluid layers and free air rises to allow accurate diagnostic visualization on the erect image.
4. A PA chest image shows the medial end of the right clavicle is 1.5 cm from the spinous process, and the medial end of the left clavicle is 3.0 cm from the spinous process. What positioning error does this indicate, and how do you correct it?
  1. Equal distances between medial clavicle ends and the spine indicate no rotation.
  2. Right clavicle end = 1.5 cm from spine; left clavicle end = 3.0 cm from spine — they are not equal.
  3. The side with the shorter distance (right) is rotated closer to the IR (or the right shoulder is rotated anteriorly toward the detector).
  4. Correction: rotate the patient's right shoulder slightly away from the IR (or the left shoulder slightly toward it) until the midsagittal plane is parallel to the IR, then re-expose.
Answer: The image shows patient rotation — the right side is rotated toward the IR. Reposition the patient so the midsagittal plane is perpendicular to the IR and the shoulders are equidistant from the detector.
In class: Using an anthropomorphic phantom or positioning mannequin, produce PA, lateral, AP lordotic, and lateral decubitus chest images and evaluate each against a 10-point positioning checklist covering anatomy visualization, collimation, exposure indicator, and motion. · Perform AP, oblique, and lateral abdomen projections for acute abdominal series protocol; measure exposure indicator values and compare against the department reference range, documenting any repeat and its cause. · Role-play a contrast-study workflow for an upper GI series — reviewing the requisition, confirming contrast allergy history, explaining the procedure to a simulated patient, and critiquing a set of 10 provided fluoroscopic spot images for positioning accuracy and diagnostic adequacy.
Materials: Radiographic positioning unit with phantom, digital radiography detector or CR cassettes, positioning sponges and aids, Bontrager's Textbook of Radiographic Positioning and Related Anatomy (current edition), departmental technique chart, exposure indicator reference values
Check: Each projection scored on 10-point positioning checklist; student achieves 8/10 or higher on every required projection and documents all repeats with cause-and-correction — pass 80%.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Radiographic Procedures
1. For a routine PA chest radiograph, which SID is standard and what is the primary reason for using it?
Radiographic Procedures
2. A patient arrives for an acute abdominal series but cannot stand. Which projection best substitutes for the erect AP abdomen to detect free intraperitoneal air?
Radiographic Procedures
3. During an upper GI series, the radiologist asks you to position the patient to best profile the duodenal bulb and pylorus. Which position is most appropriate?
Patient Care and Education
4. A patient states he had a severe reaction to shellfish in the past. He is scheduled for an upper GI series using barium sulfate. What is the most appropriate action for the limited technologist?
Radiographic Procedures
5. On a PA chest image, both costophrenic angles are cut off at the bottom of the image. What is the most likely positioning error?
Radiation Protection
6. Which statement best describes the ALARA principle as it applies to repeat radiographic exposures?
Radiographic Procedures
7. An AP abdomen image shows the symphysis pubis is not included, but the diaphragm is fully visible. What corrective action should be taken for the repeat?
Image Production and Evaluation
8. The exposure indicator for a lateral abdomen projection reads significantly below the department reference range. What is the most important implication for the patient?
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