How to Scan a Knee MRI Protocol

Are you looking to improve your knee MRI skills?

The knee MRI protocol is essential for diagnosing knee pain and injuries, including ligament tears, cartilage wear, and joint inflammation.

This step-by-step guide is for MRI students and technologists who wish to improve their professional skills and master the knee MRI protocol.

What you will learn:

1. Key factors in knee MRIs, including trade-offs.
2. Patient and scanner setup tips.
3. Best pulse sequences and planning techniques.
4. Ways to avoid common artifacts.
5. Qualities of great knee images.

The knee is a complex joint we use for daily for many activities — walking, running, and moving with stability. It absorbs impact, supports body weight, and enables a wide range of motion.

Because of its high use and susceptibility to injuries, the knee is one of the most frequently examined areas in MRI. Imaging helps assess ligament tears, cartilage damage, and other conditions affecting mobility and function.

How to Balance the 3 Trade-offs in Knee MRIs

In MRI, we always face a trade-off between 3 key metrics:

1. Scan Time: How fast a pulse sequence can be completed.
2. Resolution: How much detail the image can display.
3. SNR: How clear the image is, i.e. how much signal relative to noise.

Improving one of these metric reduces the performance of the others. To decide what trade-offs to make, we must consider the needs of each clinical situation.

For knee MRIs: This is a small area with many complex structures. And while knee protocols are commonly requested, this scan can often be completed relatively quickly.

Therefore, we typically 1) prioritize resolution, 2) maintain strong SNR for clarity, and 3) optimize scan time as needed for knee MRIs.

High resolution ensures we can see all the tiny bone structures and complex joints of the knee clearly, and spot any subtle abnormalities. However, we must still ensure a strong SNR and adequate scan time too.

Knee Health Conditions – And the MRI Sequences That Detect Them

The knee MRI study can help us diagnose a wide range of health conditions. The table below lists some of the most common conditions — and what pulse sequences that detect them:

The step-by-step guide below will show you how to set up and perform a knee MRI protocol in practice.

We will perform the protocol in 3 parts:

1. Set up the Patient and MRI Scanner
2. Plan and Acquire the Protocol Sequences
3. Review the Images

Part 1: Set up the Patient and MRI Scanner

1. Position the Patient in the Scanner

Lay the patient feet-first and supine (on their back) with the knee centered at the scanner’s isocenter.

Positioning the patient feet-first increases comfort and reduces motion artifacts, especially in those who may feel anxious in enclosed spaces.

Use a dedicated knee hard coilor flex coil to ensure high-resolution imaging. This coil provides strong signal reception and full coverage of the joint, including cartilage, ligaments, and menisci.

✅ Correct Patient Positioning:

2. Check the Scanner’s Hardware Settings

Once the patient is in place, review your scanner’s hardware settings.

In this guide, we will use the following settings:

This hardware setup is widely used in clinical practice. It balances acquisition time, image quality, and patient comfort.

3. Capture the Initial Localizer Images

Before we can perform any MRI protocol, we must always capture initial localizer images of the patient. These images act as a guide for planning the detailed scans we will perform next.

We should always capture localizers in three planes:

1. Axial
2. Sagittal
3. Coronal

Once acquired, upload the initial localizer images into the three viewports.

Then, scroll through each of the image stacks to locate a central slice that clearly shows the anatomy of the knee.

✅ Correct Setup of Localizer Images for Knee MRI:

Part 2: Plan and Acquire the Protocol Sequences

When all preparations are ready, we can start planning and acquiring the protocol sequences.

Let’s go through the pulse sequences that a standard knee MRI protocol includes, why we perform them, and how to set them up.

The 7 Sequences of a Standard Knee MRI

1. Sagittal PD FS (Proton Density Fat-Saturated)
2. Coronal PD FS
3. Axial PD FS
4. Sagittal T1
5. Coronal T2
6. Sagittal PD FS ACL (Anterior Cruciate Ligament)
7. Coronal PD FS ACL

We mainly use proton density fat-saturated sequences for this study. This type of sequence provides excellent soft tissue contrast, which helps us see the knee’s joint structures, ligaments, and cartilage clearly. PD FS also highlight fluids while suppressing signal from fat, letting us detect fluid-related abnormalities like edema or inflammation.

In the sections below, we go through how to plan and set up each sequence.

1. Sagittal PD FS

✅ Correct Planning:

Planning Instructions:

• Use the lateral condyle of the femur as the anatomical reference.
• Align the slices as follows:
  • Axial Localizer: Parallel to the lateral condyle of the femur.
  • Sagittal Localizer: Parallel to the anterior cruciate ligament.
  • Coronal Localizer: Parallel to the midline of the femur and tibia.
• Add enough slices to cover fully cover the knee from right to left.
• Center the slices and adjust the slice thickness and gap for optimal spatial resolution.

Parameters for Sagittal PD FS:

2. Coronal PD FS

✅ Correct Planning:

Planning Instructions:

• Use the medial and lateral condyles of the femur as the anatomical reference.
• Align the slices as follows:
  • Axial Localizer: Parallel to the medial and lateral condyles of the femur.
  • Sagittal Localizer: Parallel to the midline of the femur and tibia.
• Add enough slices to cover the knee from anterior to posterior.
• Center the slices and adjust the slice thickness and gap for optimal spatial resolution.

Parameters for Coronal PD FS:

3. Axial PD FS

✅ Correct Planning:

Planning Instructions:

• Use the femur, tibia, and meniscus as anatomical references.
• Align the slices as follows:
  • Sagittal Localizer: Perpendicular to the femur and tibia, and parallel to the meniscus.
  • Coronal Localizer: Parallel to the lateral and medial condyles of the femur.
• Add enough slices to cover the knee joint, from the patella’s border (upper part of the knee) down to the tibial tuberosity.
• Center the slices and adjust the slice thickness and gap for optimal spatial resolution.

Parameters for Axial PD FS:

4. Sagittal T1 TSE

✅ Correct Planning:

Planning Instructions:

• Copy the slice geometry and planning from the sagittal PD FS sequence.
• Keep the same slice angulation, coverage, and positioning to ensure images of different contrasts can be clearly compared.

Parameters for Sagittal T1 TSE:

5. Coronal T2 TSE

✅ Correct Planning:

Planning Instructions:

• Copy the slice geometry and planning from the coronal PD FS sequence.
• Keep the same slice angulation, coverage, and positioning to ensure images of different contrasts can be clearly compared.

Parameters for Coronal T2 TSE:

6. Sagittal PD FS ACL (Anterior Cruciate Ligament)

✅ Correct Planning:

Planning instructions:

• Use the axial localizer to identify the anterior cruciate ligament (ACL).
• Align the slices as follows:
  • Axial Localizer: Parallel to the ACL, from its origin to insertion.
  • Sagittal Localizer: Parallel to the ACL.
• Set a thinner slice thickness and gap for high-resolution ligament imaging.
• Limit the number of slices to cover only the ligament. Then, center the slice package.

Parameters for Sagittal PD FS ACL:

7. Coronal PD FS ACL

✅ Correct Planning:

Planning instructions:

• Use the previous sagittal PD FS ACL image for planning.
• Align the slices as follows:
  • Sagittal Localizer: Parallel to the ACL, from its origin to insertion.
  • Coronal Localizer: Parallel to the meniscus.
• Set thin slice thickness and gap for high-resolution imaging.
• Limit the number of slices to cover only the ligament. Then, center the slice package.

Parameters for Coronal PD FS ACL:

How to Avoid Artifacts When Planning the Sequences

The table below lists the 6 common knee artifacts, and what techniques you can use to avoid them:

Part 3: Review the Images

Finally, we will review the images to ensure all the anatomical information we need is clear.

These key structures must be clearly visible in a knee MRI:

1. Articular cartilage of the femur, tibia, and patella
2. Menisci (medial and lateral)
3. Ligaments, including ACL, PCL, MCL, and LCL
4. Tendons, including quadriceps and patellar tendons
5. Synovial fluid and joint capsule
6. Bone marrow and surrounding soft tissues

Below, we will go through all the different image contrasts and explain their specific role in imaging the knee.

PD Fat Saturated – Best for Soft Tissues, Cartilage, and Fluid-Sensitive Pathologies

Proton Density Fat-Saturated (PD FS) imaging provides high contrast between soft tissues while suppressing fat, making it ideal for evaluating joint structures.

In knee MRI, PD FS sequences are the gold standard for detecting ligament injuries, meniscal tears, cartilage damage, and joint effusions. It allows for a detailed evaluation of bone marrow edema, tendonitis, and synovial inflammation, making it essential for diagnosing both traumatic and degenerative conditions.

✅ Sagittal PD FS of the Knee – Correct Image:

The sagittal PD FS sequence provides a side view of the knee, which lets us:

• Assess the ACL and PCL in detail for fiber integrity and partial or full tears.
• Visualize menisci from anterior to posterior horns.
• Evaluate the patellar and quadriceps tendons.
• Detect bone marrow edema in the femoral condyles and tibial plateau.

✅ Coronal PD FS of the Knee – Correct Image:

The coronal PD FS sequence provides a frontal view of the knee, focusing on:

• Medial and lateral menisci, ideal for detecting horizontal or radial tears.
• Collateral ligaments (MCL & LCL) for sprains, tears, or thickening.
• Bone marrow signal changes, including stress fractures or contusions.

✅ Axial PD FS of the Knee – Correct Image:

The axial PD FS sequence provides a top-down view, useful for:

• Cartilage damage and patellar tracking disorders in the trochlear groove.
• Joint effusion and synovial thickening.
• Assessing the posterior cruciate ligament (PCL) from a different angle.

T1 TSE – Highlight Fat-Containing Tissues and Structural Abnormalities

T1-weighted imaging makes fat appear bright and fluid dark. This contrast is ideal for fat-rich tissues and structural abnormalities. Because fat is solid and well-defined, anatomical structures become clearer in T1 – as we can easier see where different solid tissues, like muscle and fat, meet.

In knee MRI, T1 sequences are essential for evaluating bone marrow, fractures, and fatty structures such as Hoffa’s fat pad. T1 is also useful for detecting subacute hemorrhage, osteonecrosis, and tumors because it differentiates normal fatty marrow from pathological changes.

✅ Sagittal T1 of the Knee – Correct Image:

The sagittal T1 sequence provides a longitudinal view, showing:

• Bone marrow composition and any changes from fractures, marrow edema, or neoplasms.
• Meniscal signal intensity, helping differentiate normal fibrocartilage from abnormal signal changes.
• Structural integrity of ligaments when compared with PD FS sequences.

T2 TSE – Highlight Fluid-Related Tissues and Conditions

T2-weighted imaging makes fluids appear bright. This contrast is ideal to detect tissues and abnormalities associated with high water content.

In knee MRI, T2 sequences are ideal for assessing joint effusion, meniscal cysts, synovitis, and cartilage defects. It is particularly useful for evaluating bony edema and inflammatory conditions such as rheumatoid arthritis or post-traumatic swelling.

✅ Coronal T2 of the Knee – Correct Image:

The coronal T2 sequence provides a frontal perspective, showing:

• Joint effusion and synovitis in the medial and lateral compartments.
• Cystic changes in menisci, including meniscal cyst formation.
• Cartilage defects in weight-bearing areas of the femur and tibia.

PD FS ACL – Focused ACL Imaging for Ligament Integrity

A dedicated PD FS sequence for the ACL is optimized to evaluate ligament fiber continuity, partial tears, and ligament edema. It allows for a more detailed view of ligamentous injuries, bone bruising, and secondary stabilizers.

In knee MRI, PD FS ACL sequences help identify partial or full-thickness ACL tears, fiber disruptions, and associated bone marrow edema from trauma. They are essential for pre-surgical planning and post-injury assessment.

✅ Sagittal PD FS ACL – Correct Image:

The sagittal PD FS ACL sequence provides a direct look at the ACL, showing:

• ACL fiber integrity, including partial vs. complete tears.
• Bone marrow bruising patterns in the lateral femoral condyle and tibial plateau
• Segond fractures, which indicate ACL-associated avulsions

✅ Coronal PD FS ACL – Correct Image:

The coronal PD FS ACL sequence provides an alternative angle of the ACL, helping assess:

• ACL orientation, in relation to the lateral femoral condyle.
• Signs of rotational instability, including deep lateral femoral notch sign.
• Meniscotibial ligament injuries, often associated with ACL tears.

Final Checks:

• Ensure the field of view covers all relevant anatomy.
• Verify that contrast, resolution, and signal-to-noise ratio meet your clinical requirements.

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