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Formus Atlas – CT Scan Protocol & Case Output Guide

CT Scan Protocol

Correctly collected CT scans are crucial for the accuracy of Formus Atlas. Please read the following instructions carefully before scanning.

The prevention of motion artefacts is critical for the accuracy of 3D modelling and templating. Instruct the patient on the importance of holding still during the scan.

The following minimum criteria needs to be met to enable successful upload of the radiological image:

Scan Parameters (for all radiological scanners)

Slice Thickness 2.0 mm
Slice Spacing 1.6 mm, all slices must be overlapping or contiguous.
Pixel Size 1.0 mm by 1.0 mm in the axial plane.
Field of View The image should encompass the entire pelvis and femurs down to the knee. The FoV should not change during the scan.
Table Position The CT stage must not be raised or lowered between slices. The X and Y centering must not be altered between slices.
Matrix 512x512 matrix preferred.
Algorithm Soft-tissue algorithm with no edge enhancements. Do not use bone algorithm. Do not use metal artefact reduction.
Energy 120 kVp Do not use low-dose protocol
Patient Orientation True axial only, no oblique orientations.
Photometric Interpretation MONOCHROME2 only. Lower the CT value, the darker the voxel should appear.

DICOM Export Settings

The following settings are to be used when exporting the scan to CD/DVD or file:

Format DICOM with no compression
Slice Thickness 2.0 mm
Slice Spacing 1.6 mm, all slices must be overlapping or contiguous.
Pixel Size 1.0 mm by 1.0 mm in the axial plane.
Field of View The image should encompass the entire pelvis and femurs down to the knee.
Matrix 512x512 matrix preferred.
Patient Orientation True axial only, NO oblique orientations.

Case Output Guide

This evaluation version of Atlas supports 3D CT segmentation, landmarking, and measurements for the hip joints. The table below describes how the output may differ in various use cases.

Case Description Will generate .PLY Model Files? Will generate .CSV Landmarks & Measurement Files? Notes
Ideal Case
  • CT Scan as per hip planner protocol
  • CT Scan includes both hemipelvises and both femurs
  • healthy patient
 Yes Yes
Osteophytes Yes Less Accurate
Dysplasia Yes Less Accurate
One Hip implant Yes Less Accurate
Two Hip implants Yes Less Accurate
Amputation Yes Less Accurate
Late Stage Arthritis Less Accurate No
Fractures Yes Less Accurate Landmarks and measurements will use the largest piece of bone
Partial Scan missing hemipelvises or femurs Yes Yes Only models, landmarks, and measurements of available bones will be generated
Protocol not followed: High Resolution Yes* Yes* * Processing may take longer
Protocol not followed: Wrong brightness Yes* Yes* * May lead to unexpected outputs such as bone being detected as metal
Protocol not followed: Only proximal femur imaged Yes Less Accurate Distal femur is predicted
Protocol not followed: full body scan No No

Landmark Definitions

Landmark Name Name in output file Definition
Femoral Head Center headCenter Centre of rotation of the femoral head
Medial Epicondyle medialEpicondyle Prominence on the medial distal femur
Lateral Epicondyle lateralEpicondyle Prominence on lateral distal femur
Greater Trochanter greaterTrochanter Most proximal/anterior point on the greater trochanter
Femoral Neck Saddle neckSaddle Lowest point on the upper surface of the femoral neck
Posterior of Lateral Femoral Condyle posteriorCondyleLateral Most posterior point of the articular surface of the lateral femoral condyle
Posterior of Medial Femoral Condyle posteriorCondyleMedial Most posterior point of the articular surface of the medial femoral condyle
Femoral Neck Centroid neckCentroid Centroid of the femoral neck
Left Acetabular Centre leftAcetabularCentre Centre of rotation of the left acetabulum
Left Anterior Superior Iliac Spine leftAsis Most anterior aspect of the left iliac crest
Left Posterior Superior Iliac Spine leftPsis Most posterior aspect of the left iliac crest
Left Pubic Symphysis leftPubicSymphysis Anterior superior midpoint (or most prominent point) of the left pubic symphysis.
Left Pubic Tuberosity leftPubicTuberosity Most lateral and prominent point of left pubic tubercle of the left pubic crest.
Left Ischial Spine leftIschialSpine Most posterior point on the sharp prominence of the left ischium
Left Ischial Tuberosity leftIschialTuberosity Most inferior point on the ischial tuberosity of the left ischium
Left Anterior Tranverse Acetabular Ligament leftAtrans Anterior attachment of the left transverse acetabular ligament
Left Posterior Transverse Acetabular Ligament leftPtrans Posterior attachment of the left transverse acetabular ligament
Left Acetabular Fossa leftFossa Centre of the fossa of the left acetabulum
Left Superior Acetabular Rim leftAcetabularRimSuperior Most superior aspect of the rim of the left acetabulum
Left Anterior Acetabular Rim leftAcetabularRimAnterior Left Anterior Acetabular Rim
Left Posterior Acetabular Rim leftAcetabularRimPosterior Most posterior aspect of the rim of the left acetabulum
Right Acetabular Centre rightAcetabularCentre Centre of rotation of the right acetabulum
Right Anterior Superior Iliac Spine rightAsis Most anterior aspect of the right iliac crest
Right Posterior Superior Iliac Spine rightPsis Most posterior aspect of the right iliac crest
Right Pubic Symphasis rightPubicSymphysis Anterior superior midpoint (or most prominent point) of the right pubic symphysisq
Right Pubic Tuberosity rightPubicTuberosity Most lateral and prominent point of right pubic tubercle of the right pubic crest.
Right Ischial Spine rightIschialSpine Most posterior point on the sharp prominence of the right ischium
Right Ischial Tuberosity rightIschialTuberosity Most inferior point on the ischial tuberosity of the right ischium
Right Anterior Tranverse Acetabular Ligament rightAtrans Anterior attachment of the right transverse acetabular ligament
Right Posterior Transverse Acetabular Ligament rightPtrans Posterior attachment of the right transverse acetabular ligament
Right Acetabular Fossa rightFossa Centre of the fossa of the right acetabulum
Right Superior Acetabular Rim rightAcetabularRimSuperior Most superior aspect of the rim of the right acetabulum
Right Anterior Acetabular Rim rightAcetabularRimAnterior Right Anterior Acetabular Rim
Right Posterior Acetabular Rim rightAcetabularRimPosterior Most posterior aspect of the rim of the right acetabulum

Measurement Definitions

Measurement Name Name in output file Definition
Femoral Head Diameter FemurHeadDiameter Diameter of a sphere fitted to the femoral head
Femoral Neck Width FemurNeckWidth Width of the femoral neck in coronal plane in the minimum cross-section along the neck axis
Femoral Neck Diameter FemurNeckDiameter Diameter of the narrowest part of the femoral neck (calculated as 2 times the min distance of neck points to the neck axis)
Femoral Neck Shaft Angle FemurNeckShaftAngle Angle between the femoral neck axis and the femoral shaft axis
Femoral Neck Axis Length FemurNeckAxisLength Length of the femoral neck calculated as the distance between where the femoral neck axis exits the femoral head and the greater trochanter
Femoral Length Medial FemurLengthMedial Length of the femur calculated as the distance from the most proximal point of the femoral head to the most distal point on the medial condyle
Femoral Length Lateral FemurLengthLateral Length of the femur calculated as the distance from the most proximal point of the greater trochanter to the most distal point on the lateral condyle
Femoral Subtrochanteric Diameter FemurSubtrochantericDiameter Diameter of the femoral shaft below the lesser trochanter (spherical fit)
Femoral Subtrochanteric Width FemurSubtrochantericWidth Width of the femoral shaft just below the lesser trochanter in the coronal plane
Femoral Midshaft Diameter FemurMidshaftDiameter Diameter of the femoral shaft halfway down the shaft (spherical fit)
Femoral Midshaft Width FemurMidshaftWidth Width of the femoral shaft halfway down the shaft in the coronal plane
Femoral Epicondylar Width FemurEpicondylarWidth Distance between the most medial and most lateral points of the femoral epicondyles
Femoral Anteversion Angle (Sugano Method) FemurAnteversionAngleSugano Anteversion angle of the femur calculated between the femoral neck axis (formed by the centroid of the femoral head and the centroid of the femoral neck) and the posterior condylar axis (formed by the most posterior points of the medial and lateral femoral condyles) projected onto a plane defined by the anatomical femoral shaft axis.
Femoral Anteversion Angle (Lee Method) FemurAnteversionAngleLee Anteversion angle of the femur calculated between the femoral neck axis (formed by the centroid of the femoral head and the saddle on the femoral neck) and the posterior condylar axis (formed by the most posterior points of the medial and lateral femoral condyles) projected onto a plane defined by the anatomical femoral shaft axis.
Hemipelvis Hip Joint Center Radius HemipelvisHjcRadius Radius of a sphere fitted to the acetabulum
Hemipelvis Acetabulum Diameter HemipelvisAcetabulumDiameter Diameter of a sphere fit to the acetabulum
Hemipelvis Ilial Depth HemipelvisIlialDepth Distance between the ASIS and PSIS
Hemipelvis Operative Anteversion HemipelvisOperativeAnteversion Angle between acetabular axis as projected onto the sagittal plane and the coronal plane
Hemipelvis Operative Inclination HemipelvisOperativeInclination Angle between the acetabular axis and the sagittal plane. A.k.a. abduction of the acetabular axis
Hemipelvis Anatomical Anterversion HemipelvisAnatomicalAnteversion Angle between the acetabular axis, as projected onto the transverse plane, and the transverse axis
Hemipelvis Anatomical Inclination HemipelvisAnatomicalInclination Angle between the acetabular axis and the longitudinal axis of the patient
Hemipelvis Radiographic Anteversion HemipelvisRadiographicAnteversion Angle between the acetabular axis and the coronal plane. A.k.a. planar anterversion
Hemipelvis Radiographic Inclination HemipelvisRadiographicInclination Angle between the longitudinal axis of the body and the acetabular axis that is projected onto the coronal plane. A.k.a. projected inclination
Pelvis Inter-ASIS Distance pelvisInterAsisDistance Distance between the left and right anterior superior iliac spines (ASIS)
Pelvis Inter-PSIS Distance pelvisInterPsisDistance Distance between the left an right posterior superior iliac spines (PSIS)
Pelvis Inter-PS Distance pelvisInterPsDistance Distance of the joint space of the pubic symphysis measured proximally
Pelvis Inter-HJC Distance pelvisInterHjcDistance Distance between the left and right hip joint centres (HJC)
Pelvis Leg Length Difference pelvisLegLengthDifference Difference in distances between leg lengths of the left and right leg (positive value means left side is longer), where the leg length is calculated as the distance in the coronoal plane between the lesser trochanter and a line between the most inferior points of the left and right ishial tuberosities