Thoracic and lumbar spine X-rays are among the most frequently ordered examinations in radiology — and among the most challenging to perform correctly. The thoracic spine presents unique difficulties because of superimposition by the ribs, lungs, and mediastinal structures. The lumbar spine, while more forgiving in terms of penetration, demands precise patient positioning and centering to demonstrate the intervertebral disc spaces, articular facets, and the critical L5-S1 lumbosacral junction.
This guide covers every standard projection for both the thoracic and lumbar spine, including special views such as the scoliosis series and the spot lateral L5-S1. Whether you are a student preparing for the ARRT registry or a practicing technologist looking to refine your technique, this article will give you the centering points, breathing instructions, IR sizes, and evaluation criteria you need to produce consistently diagnostic images.
The thoracic spine consists of 12 vertebrae (T1–T12) that articulate with the 12 pairs of ribs. The lumbar spine consists of 5 vertebrae (L1–L5) that bear the majority of axial body weight. The lumbosacral junction (L5-S1) is a common site of disk pathology and is often evaluated with a dedicated spot lateral projection. The entire spine has four natural curvatures: cervical (lordotic), thoracic (kyphotic), lumbar (lordotic), and sacral (kyphotic). Understanding these curvatures is essential for correct positioning, especially on lateral projections where the X-ray beam must be centered appropriately for each region.
The AP thoracic spine is the primary frontal projection for evaluating the upper and mid-back. It is typically performed with the patient supine or erect, though erect positioning is preferred when possible to demonstrate any scoliotic curvature under weight-bearing conditions.
Center the central ray (CR) at T7, approximately 3–4 inches (8–10 cm) below the jugular notch at the level of the sternal angle (Angle of Louis). The top of the IR should be approximately 1.5–2 inches above the shoulders so that the upper border of the collimation includes C7 and T1, and the lower border includes L1.
On the ARRT exam, you will commonly be asked: "Which thoracic vertebrae are visualized on inspiration vs expiration?" On inspiration, the diaphragm descends, potentially obscuring T11–T12. On expiration, the diaphragm rises, allowing T11–T12 to be seen. The standard is to suspend at the end of expiration for most AP T-spine radiographs. Another high-yield fact: the sternal angle (Angle of Louis) corresponds to the level of T4–T5, and the jugular notch is at the level of T2–T3.
The lateral thoracic spine is arguably the most technically demanding routine projection in radiography. The vertebrae must be seen through the superimposed density of the lungs, ribs, and mediastinum. A specialized breathing technique is essential.
Center the CR at T7, at the level of the sternal angle. The CR should be directed perpendicular to the IR, entering the midaxillary line at the level of T7. On a lateral projection, the T7 vertebral body is located approximately at the level of the inferior angle of the scapula.
The slow, shallow breathing technique for the lateral thoracic spine is a favorite topic on the registry. The principle is simple: the exposure time needs to be long enough to span multiple respiratory cycles (typically 6–10 breaths at a rate of 12–16 breaths/min). Modern digital systems may make this challenging because of their shorter exposure times. If the automatic exposure control (AEC) terminates the exposure too quickly, switch to a manual technique with a deliberately long exposure time (≥ 1 second) and reduced mA to maintain the mAs. This ensures the required motion blur of overlying structures.
The AP lumbar spine is a routine projection that demonstrates the lumbar vertebral bodies, pedicles, spinous processes, intervertebral disc spaces, and the psoas muscle shadows.
Center the CR at L3. The most reliable external landmark is the level of the iliac crests (the intercristal line, also known as Tuffier's line), which crosses the spine at approximately the L4 level or the L4–L5 interspace. To center at L3, position the CR approximately 1–1.5 inches (2.5–4 cm) above the iliac crests. The top of the IR should be at approximately the T12 level, ensuring the inclusion of T12 and all five lumbar vertebrae.
The iliac crests are the most reliable surface landmark for lumbar spine positioning. In most patients, the intercristal line crosses L4 or the L4–L5 interspace. For the AP projection, center 1–1.5 inches above this line to target L3. For the lateral lumbar spine, the iliac crest landmark is also used — center at the same level (L3) for a general lateral, and approximately 2 inches below the iliac crest for a spot lateral L5-S1. In larger patients, palpate firmly to identify the iliac crests accurately; in obese patients, use the level of the umbilicus as a secondary landmark (usually at L3–L4).
The lateral lumbar spine is critical for evaluating the intervertebral disc spaces, spondylolisthesis, the lumbar lordotic curve, and the lumbosacral angle.
Center the CR at L3, approximately 3–4 inches (8–10 cm) above the iliac crest, at the midcoronal plane. The CR should be directed perpendicular to the IR, entering approximately 2 inches (5 cm) posterior to the midaxillary line (at the anterior third of the distance from the posterior spinous process to the anterior abdominal wall).
The ARRT expects you to evaluate lateral lumbar spine images for rotation. On a true lateral, the posterior margins of the vertebral bodies are perfectly superimposed (like a single line). The intervertebral foramina on each side are also superimposed. If you see a double outline of the posterior vertebral body margins, the patient is rotated. Additionally, if one ilium is projected anterior to the other, pelvic rotation is present. The solution: reposition and ensure the patient's midcoronal plane is truly parallel to the IR and perpendicular to the CR.
The spot lateral (or coned lateral) of the lumbosacral junction is a dedicated view of L5–S1 used to evaluate the L5–S1 interspace, spondylolisthesis, and degenerative changes at the lumbosacral joint. It requires a cephalic angle to open the lumbosacral joint space because the normal lumbosacral angle is approximately 30–40 degrees in the adult.
Center the CR to a point 1.5–2 inches (4–5 cm) below the iliac crest and 2 inches (5 cm) posterior to the ASIS. The CR is angled cephalad as described above. Tight collimation is used — a 10 × 12 inch (24 × 30 cm) IR or smaller is appropriate.
The AP oblique projections (also known as the Scottie dog views) are used to evaluate the pars interarticularis, a common site of spondylolysis (a stress fracture of the neural arch). The ARRT commonly tests on the anatomy displayed in this projection.
Center the CR at L3 — 1–1.5 inches above the iliac crests — perpendicular to the IR.
On the AP oblique projection, the posterior elements of the lumbar vertebrae form the image of a "Scottie dog":
A radiolucent defect (break) in the neck of the Scottie dog indicates spondylolysis. This is the classic finding on the ARRT exam.
The ARRT exam loves the oblique lumbar spine. You absolutely must know: (1) A 45-degree oblique is required. Less than 45° will not adequately profile the pars interarticularis; more than 45° will superimpose the structures. (2) The side of interest for an RPO is the right side. (3) The "Scottie dog" appearance is created by the side away from the IR. For example, in an RPO position (right side down), the left-sided posterior elements are profiled and form the Scottie dog. (4) A break in the neck (pars interarticularis) = spondylolysis. If there is vertebral slippage associated with the defect, it is spondylolisthesis.
A scoliosis series is a specialized examination used to evaluate the degree of spinal curvature in patients with scoliosis. The images must be obtained with the patient in the erect (standing) position to assess the spine under weight-bearing conditions. These studies are typically performed on pediatric and adolescent patients to monitor curve progression.
The PA projection is the standard for scoliosis imaging because it reduces radiation dose to radiosensitive organs. In the PA position, the breasts and thyroid receive significantly less dose compared to the AP position. For serial follow-up examinations (which are common in growing children), this dose reduction is critical. The Image Gently campaign strongly recommends PA scoliosis imaging in pediatric patients. Always use the fastest available imaging system and tight collimation to minimize dose further.
| Parameter | AP Thoracic Spine | Lateral Thoracic Spine | AP Lumbar Spine | Lateral Lumbar Spine | Spot Lateral L5-S1 |
|---|---|---|---|---|---|
| IR Size | 14 × 17" | 14 × 17" | 14 × 17" | 14 × 17" | 10 × 12" or 8 × 10" |
| SID | 40" (100 cm) | 40" (100 cm) | 40" (100 cm) | 40" (100 cm) | 40" (100 cm) |
| kVp Range | 70–80 | 80–90 | 75–85 | 85–95 | 85–95 |
| Centering | T7 (sternal angle) | T7 (sternal angle) | L3 (1–1.5" above iliac crest) | L3 | 1.5–2" below iliac crest |
| Breathing | Suspend expiration | Slow, shallow breathing | Suspend expiration | Suspend expiration | Suspend expiration |
| CR Angle | None (perpendicular) | None (perpendicular) | None (perpendicular) | None (perpendicular) | 25–35° cephalad |
| Grid | 8:1 or 12:1 | 12:1 | 12:1 | 12:1 | 12:1 |
| Key Anatomy | Vertebral bodies, pedicles, spinous processes, costovertebral joints | Vertebral bodies, intervertebral foramina, spinous processes | Vertebral bodies, pedicles, spinous processes, psoas shadows | Vertebral bodies, disc spaces, neural foramina, spinous processes | L5-S1 interspace, sacral promontory |
Even experienced technologists encounter challenges with thoracic and lumbar spine positioning. Here are the most frequent errors and their solutions:
Thoracic and lumbar spine radiographs contribute significantly to patient radiation dose because of the multiple projections typically performed and the relatively high kVp/mAs settings required. A standard lumbar spine series (AP, lateral, spot lateral) delivers an effective dose of approximately 1.5 mSv. For reference, this is roughly equivalent to 6 months of natural background radiation.
As a radiologic technologist, you should apply the following ALARA strategies:
A study published in the American Journal of Roentgenology found that lumbar spine radiography accounts for approximately 5% of all radiographic examinations but contributes nearly 20% of the collective effective dose from diagnostic radiography. This is because of the relatively high exposure factors and the multiple projections performed. As a technologist, you can have the greatest impact on population dose by optimizing your lumbar spine technique and collaborating with referring clinicians to reduce unnecessary repeat examinations. Always ask: "Does the clinical question really require all five views?" If the answer is no, adjust the protocol accordingly.
Elderly patients often have osteoporosis, kyphosis, and degenerative changes that make positioning more challenging. The lateral thoracic spine can be particularly difficult because the patient may not be able to elevate both arms or remain still for prolonged exposures. Consider using positioning sponges liberally, and be prepared to repeat a projection if the initial image shows motion. For patients with severe kyphosis, you may need to angle the CR to compensate for the exaggerated curvature — center at the apex of the kyphotic curve rather than at a fixed vertebral level.
Patients who have undergone spinal fusion surgery have hardware (rods, pedicle screws, cages) that obscures the underlying vertebral anatomy. Follow the same positioning protocols, but inform the radiologist that hardware is present. If evaluating for hardware complications (loosening, fracture, infection), dedicated views centered on the level of the hardware may be required. Always check the patient's chart before the examination to know the extent of the fusion.
Try these ARRT-style multiple choice questions based on this article. Click an option to check your answer — correct answers turn green, wrong ones turn red.