Glossary · Clinical

MRI (magnetic resonance imaging)

MRI (magnetic resonance imaging) is a non-ionizing diagnostic imaging modality that uses strong magnetic fields and radiofrequency pulses to generate high-contrast images of soft tissues, joints, and the spine. In orthopedics, it is the primary tool for evaluating cartilage, ligaments, tendons, bone marrow, and nerves when plain radiographs are insufficient.

Verified May 8, 2026 · 7 sources ↓

Drawn from CMSMtnmedicalAjnrAAOS

Definition

Source · Editorial summary grounded in 7 cited references ↓

MRI produces cross-sectional images by detecting the response of hydrogen protons in tissue to a magnetic field and radiofrequency energy. Because it does not use ionizing radiation, it is the preferred modality for repeated or pediatric imaging. Tissue contrast is controlled by selecting different pulse sequences (e.g., T1, T2, STIR, proton-density fat-saturation), making MRI uniquely capable of differentiating tendon tears from tendinosis, bone marrow edema from cortical fracture, and disc herniation from foraminal stenosis.

In the orthopedic context, MRI is ordered to answer specific clinical questions that X-ray and CT cannot resolve: ACL integrity, rotator cuff tear grade and retraction, meniscal tear pattern, labral pathology, osteochondral lesion depth, and occult stress fractures. The imaging region and contrast status must be specified at the time of ordering because they directly determine which CPT code is appropriate for billing. For example, a knee MRI without contrast is coded 73721, whereas the same joint imaged with contrast uses 73722, and both phases together use 73723.

Gadolinium-based contrast agents are used selectively—typically for arthrography, tumor characterization, or post-operative assessment—and carry their own HCPCS billing requirements (A9579, revenue code 636 for facility claims). MRI safety screening for patients with implants or foreign bodies now has dedicated CPT codes (effective 2025) to capture the additional physician and physicist work required before scanning proceeds.

Why it matters

Selecting the wrong CPT code for an MRI—most often misidentifying whether contrast was used, or billing a joint code for a non-joint region—is one of the leading causes of radiology claim denials and post-payment audits. A single digit difference (e.g., 73721 vs. 73722) changes reimbursement and triggers payer edits; using the non-joint extremity series (73718–73720) when the joint series (73721–73723) applies, or vice versa, can constitute miscoding under CMS medical necessity rules. Additionally, ordering an MRI without linking a supported ICD-10-CM diagnosis that satisfies the LCD's 'medically necessary' threshold puts the claim at risk of denial and may require an Advance Beneficiary Notice (ABN) with modifier GZ or GA on the claim.

Common mistakes

Where people most often go wrong with this concept.

Source · Editorial brief grounded in cited references ↓

Billing a joint CPT code (e.g., 73221 for shoulder) when the scan covered a non-joint region (e.g., humerus shaft → 73218), or the reverse—these are distinct code families and are not interchangeable.
Omitting contrast-status specificity: ordering notes say 'MRI knee' without specifying without contrast, with contrast, or with-and-without, forcing the coder to guess or query, which delays claim submission.
Failing to bill gadolinium contrast separately (A9579 with revenue code 636 on facility claims) or billing it under an outdated HCPCS code (A4643 or Q9952 for dates of service after 01/01/2007).
Billing multiple body-region MRIs from a single session without appending the appropriate modifier (e.g., 59 or LT/RT laterality modifiers), which causes bundling edits under NCCI.
Missing prior authorization before scanning: many commercial payers and Medicare Advantage plans require pre-authorization for outpatient MRI; ordering without it is the second most common reason for denial.
Linking only a symptom-level ICD-10 code (e.g., M79.3 panniculitis) when a more specific diagnosis that appears on the LCD's covered-conditions list is available and documented in the chart.
Ignoring new 2025 MR safety CPT codes for patients with implants or foreign bodies, leaving physician and physicist work unbilled and under-documented.

Related codes

Codes commonly involved when this concept appears in practice.

CPT

ICD-10

M51.16 M17.11

Modifiers

LT Left side RT Right side 59 Distinct procedural service 26 Professional component

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 7 cited references ↓

01What is the difference between CPT 73721, 73722, and 73723 for knee MRI?

73721 is used when the knee is scanned without any contrast agent. 73722 applies when contrast is administered during the scan. 73723 covers a two-phase acquisition: images obtained both before and after contrast injection. Selecting the wrong code based on contrast status is a frequent cause of claim denial or post-payment audit.

02Does Medicare require prior authorization for outpatient MRI?

Traditional Medicare (Parts A and B) does not universally require prior authorization for diagnostic MRI, but coverage depends on meeting the medical necessity criteria in the applicable Local Coverage Determination (LCD). Medicare Advantage plans frequently do require prior authorization. Always verify the specific plan's requirements before scheduling.

03How is gadolinium contrast billed on a facility claim?

For dates of service on or after January 1, 2007, gadolinium-based contrast is billed using HCPCS code A9579 paired with revenue code 636 on facility (UB-04) claims. Units and the HCPCS code must both be present; omitting either triggers a claim edit. The older codes A4643 and Q9952 apply only to earlier dates of service.

04When should modifier 59 be appended to an MRI code?

Modifier 59 (or an appropriate X{EPSU} modifier) is appended when two or more MRI CPT codes for distinct body regions are billed on the same date of service and would otherwise be bundled by NCCI Procedure-to-Procedure edits. It signals that each scan represents a separate and distinct procedural service. Laterality modifiers (LT/RT) are used concurrently when bilateral structures are imaged.

05Can a non-radiologist physician bill for the professional component of an MRI interpretation?

Yes, but only if the physician independently interprets the images and prepares a written report. The professional component is reported with modifier 26 appended to the appropriate MRI CPT code. The physician must have relevant training, and the interpretation must be separately documented—it cannot be bundled into an E/M note.

06What are the new MRI safety CPT codes effective in 2025?

In 2025, new CPT codes became available to capture the additional work performed by physicians, medical physicists, and other qualified health professionals when preparing patients with implants or foreign bodies for MRI. These codes reflect safety assessments, protocol modifications, and implant management work that was previously unbillable. The American College of Radiology led the code change application.

07What ICD-10 diagnosis is needed to support MRI medical necessity for a knee?

The diagnosis must appear on the applicable CMS LCD covered-conditions list for musculoskeletal MRI. Common supported diagnoses include internal derangement of the knee (M23.x), ligament sprain with suspected structural tear (S83.x), osteochondral defect, or symptoms that have failed conservative management and are documented as such. A symptom-only code such as knee pain (M25.561) alone may not satisfy medical necessity without supporting clinical context.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

When Mira detects an orthopedic MRI order in the clinical note, it performs the following actions automatically: 1. REGION + LATERALITY CAPTURE — Mira parses the note for the body region (e.g., 'left knee,' 'lumbar spine,' 'right shoulder') and flags ambiguous entries (e.g., 'MRI extremity') for provider clarification before order finalization. 2. CONTRAST STATUS — Mira reads contrast documentation in the impression or order field and maps to the correct CPT triplet (e.g., without → 73721; with → 73722; without and with → 73723). If contrast status is absent, Mira inserts a structured query rather than defaulting. 3. JOINT vs. NON-JOINT ROUTING — Mira distinguishes joint-series codes (73221–73223, 73721–73723) from non-joint-series codes (73218–73220, 73718–73720) based on anatomic location extracted from the note. 4. DIAGNOSIS LINKAGE — Mira suggests the most specific ICD-10-CM code documented in the encounter that satisfies CMS LCD medical necessity criteria for the ordered MRI region. If only a symptom code is present, Mira flags the gap and prompts the provider to confirm or add a more specific diagnosis. 5. MODIFIER RECOMMENDATIONS — When multiple MRI regions are ordered in the same session, Mira appends modifier 59 (or appropriate anatomic modifiers LT/RT) and alerts the coder to potential NCCI bundling edits. 6. IMPLANT SAFETY FLAG — If the note documents a cardiac device, cochlear implant, spinal stimulator, or other MR-conditional implant, Mira surfaces the 2025 MR safety CPT codes and routes an alert to the ordering provider to confirm safety clearance is documented before scan completion. 7. ABN TRIGGER — If the linked diagnosis does not appear on the applicable LCD covered-conditions list, Mira generates an ABN workflow and pre-populates modifier GA or GZ on the claim draft pending provider review.

See Mira's approach

Related terms

CPT code Coding

A CPT code is a standardized five-digit numeric code, maintained by the AMA, that identifies a specific medical or surgical service for billing and reimbursement purposes. In orthopedics, CPT codes cover everything from office visits and joint injections to complex spinal fusions and total joint replacements.

ICD-10-CM Coding

ICD-10-CM (International Classification of Diseases, Tenth Revision, Clinical Modification) is the U.S. diagnosis coding system used on every claim to communicate why a service was performed, establish medical necessity, and support reimbursement. Maintained by CMS and CDC, it has been required for all HIPAA-covered entities since October 1, 2015.

Modifier Coding

A modifier is a two-character code—numeric, alphanumeric, or alpha—appended to a CPT or HCPCS code to signal that a service was performed under circumstances that differ from the standard description, without altering the fundamental meaning of the code itself.

NCCI (National Correct Coding Initiative) Coding

The National Correct Coding Initiative (NCCI) is a CMS program of automated prepayment edits that prevent Medicare and Medicaid from paying for procedure code combinations that are incorrectly billed together or billed in quantities that exceed what is clinically reasonable.

MUE (Medically Unlikely Edit) Coding

An MUE (Medically Unlikely Edit) is a CMS-established cap on the maximum units of service (UOS) that Medicare will reimburse for a given HCPCS/CPT code billed by the same provider for the same patient on the same date of service. Claims exceeding the MUE value are automatically denied at the line level.

Prior authorization Billing

Prior authorization (PA) is a payer requirement that a provider obtain approval before delivering a specific service, procedure, or item—otherwise the claim will be denied regardless of medical necessity. Approval is granted when submitted clinical documentation meets the payer's coverage criteria.