Alpha Angle Measurement by CT

Purpose

An automated method for alpha angle measurement to assist in the determination of femoroacetabular impingement

Tag(s)

#FAI, #alpha angle, #CT

Panel

Musculoskeletal Panel

Define-AI ID

19050028

Originator

Martin Torriani
Lead Martin Torriani

Panel Chair

Jay Patti

Panel Reviewers

Musculoskeletal Panel

License

Creative Commons 4.0 

Status Public Commenting 
RadElement Set RDES119
                               

Clinical Implementation


Value Proposition


Femoroacetabular impingement (FAI) is an entity in which abnormal osseous morphology of the femoral neck (CAM FAI) or acetabulum (pincer FAI) may cause osseous impact that leads to fibrocartilage (labrum) tears, cartilage loss, early degenerative changes and pain. Using multiplanar reformatted images, hip CT protocols can produce images that allow for detection of CAM FAI, however the measurement process is laborious and may present intra- and inter-observer variability. AI meeting this use case would help to make these measures more efficient and improve patient care by providing an initial assessment on the potential presence of CAM FAI.

Narrative(s)


A 30-year-old patient presents for hip CT due to pain. An algorithm evaluates the image and may also compare this exam with multiple prior exams. The algorithm detects if alpha angle is abnormal (> 55 degrees) to assist the radiologists in the interpretation and raise the possibility of FAI.

Workflow Description


Identification of appropriate pulse sequence containing oblique axial images.Identification of best oblique axial image on which to perform measures. Placement of measurement calipers on axial image. Output of alpha angle.

Considerations for Dataset Development



Procedures(s)

{CT Hip}

View(s)

{Dedicated oblique axial}

Sex at Birth

{Male, Female}

Age

[18-50]

Technical Specifications


Inputs

DICOM Study

 

Procedure

CT Hip

Views

Dedicated oblique axial

Data Type

DICOM

Modality

CT

Body Region

Lower Extremity

Anatomic Focus

Hip




Primary Outputs

 

Alpha Angle

RadElement ID

RDE775

Definition

Alpha angle

Data Type

Numeric

Value Set

N/A

Units

Degrees

Future Development Ideas


  • FAI can be of pincer type and would require measures of excessive acetabular coverage, which could be performed.
  • Recent studies show that CAM FAI may require assessment of alpha angle on multiple images, which could require a 3D acquisition of the hip for this purpose.
  • Dedicated Use Case for FAI or alpha angle on radiographs.