Method for periprosthetic bone mineral density measurement

• US 5,306,306 A
• Filed: 06/07/1993
• Issued: 04/26/1994
• Est. Priority Date: 02/13/1991
• Status: Expired due to Term

• Current Assignee: Lunar Corporation (GE Aerospace)
• Original Assignee: Lunar Corporation (GE Aerospace)
• Inventors: Mazess, Richard B., Bisek, Joseph P., Hanson, James A.
• Primary Examiner(s): Green, Randall L.
• Assistant Examiner(s): WILLSE, DAVID H
• Application Number:
  US08/073,264
• Time in Patent Office: 323 Days
• Field of Search: 623/16, 606/76-77, 128/661.03, 128/653.1, 378/4, 378/89, 378/90, 250/358.1
• US Class Current: 600/407
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4035 the source being combined with a filter or grating
• CPC Class Codes: A61B 6/463 characterised by displaying multiple images or images and diagnostic data on one display
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• CPC Class Codes: A61B 6/505 for diagnosis of bone
• CPC Class Codes: A61F 2/28 Bones joints A61F2/30
• CPC Class Codes: A61F 2/32 for the hip
• CPC Class Codes: A61F 2/367 Proximal or metaphyseal parts of shafts trochanteric devices connected to said proximal parts A61F2/30739
• CPC Class Codes: A61F 2/3676 Distal or diaphyseal parts of shafts
• CPC Class Codes: A61F 2/44 for the spine, e.g. vertebrae, spinal discs
• CPC Class Codes: A61F 2/4657 Measuring instruments used for implanting artificial joints for surgical instruments A61B90/06
• CPC Class Codes: A61F 2/468 Testing instruments for artificial joints for testing non-implantable prostheses A61F2/76
• CPC Class Codes: A61F 2002/3008 radio-opaque, e.g. radio-opaque markers
• CPC Class Codes: A61F 2240/008 Means for testing implantable prostheses
• CPC Class Codes: A61F 2250/0098 radio-opaque, e.g. radio-opaque markers
• CPC Class Codes: A61F 2310/00011 Metals or alloys
• CPC Class Codes: A61F 2310/00179 Ceramics or ceramic-like structures
• CPC Class Codes: G01T 1/163 Whole body counters hand or feet contamination measurement G01T1/167; lung, brain, thyroid, kidney or the like counting G01T1/16
• CPC Class Codes: G06T 2207/30008 Bone
• CPC Class Codes: G06T 7/62 of area, perimeter, diameter or volume
• CPC Class Codes: Y10S 623/914 : Bone

Abstract

A method of evaluating bone density around a prosthesis establishes an implant boundary at the edge of the prosthesis and creates a measurement boundary displaced from this implant boundary toward the bone producing a conformed region of interest. Matched histograms of bone density in a lateral and medial such region of interest may be displayed to evaluate symmetrical stress effects. Alternatively, bone density may be displayed plotted along an axis cutting across the medial and lateral sides. Fiducial points are identified from the bone and implant morphology to ensure that either display will have a repeatable reference and hence that such displays will be directly comparable to later and earlier displays thereby aiding in the detection of bone change.

Claims

1. A method of using a dual energy densitometer having a visual display to determine bone mineral density in a patient having a bone with a prosthetic implant, the method comprising the steps of:

a) scanning with said dual energy densitometer said patient in the region of said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said bone and implant at a defined location in the internal structure of said patient in said region, the matrix holding a corresponding location and data value for each data element;

b) analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) using a plurality of the boundary data elements to form an implant boundary;

d) establishing a measurement boundary which conforms to said implant boundary and is translated from said implant boundary by a predetermined distance along a translation axis;

e) calculating bone mineral density within a plurality of segments contained between the implant boundary and the measurement boundary and displaced along the implant boundary to produce a set of segment values indicative of the density of the bone adjacent to said implant; and

f) displaying on said visual display a plot of segment values versus distance along the implant boundary.

2. The method of claim 1 including the step of analyzing the matrix of data elements to identify the position of a fiducial point of the bone within the matrix of data elements and referencing the plot of segment values to said fiducial point.

3. The method of claim 1 wherein said implant boundary conforms to the shape of said implant and isolates and removes from the calculation of bone density data elements resulting from absorption of energy by said implant.

4. The method of claim 1 wherein the implant has opposed medial and lateral edges and where the plot of segment values is composed of a medial and lateral histogram with corresponding segment values plotted along first axes and distance along the implant boundary plotted along second axes and where the second axes are aligned so that the corresponding medial lateral segment values are aligned.

5. A method of using a dual energy densitometer having a visual display to determine bone mineral density in a patient having a bone with a prosthetic implant, the method comprising the steps of:

a) scanning with said dual energy densitometer said patient in the region of said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said bone and implant at a defined location in the internal structure of the patient in said region, the matrix holding a corresponding location and data value for each data element;

b) analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) using a plurality of the boundary data elements to form an implant boundary

d) identifying the position of a fiducial point of the bone within the matrix of data elements;

e) calculating bone mineral density along a measurement axis having a predetermined distance and orientation with respect to said fiducial point and including a portion of the bone adjacent said implant as defined by the implant boundary; and

f) displaying on said visual display a plot of the bone mineral density along said measurement axis.

6. A method of using a dual energy densitometer having a visual display to determine bone mineral density in a patient having a bone with a prosthetic implant, the method comprising the steps of:

a) scanning with said dual energy densitometer said patient in the region of said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said bone and implant at a defined location in the internal structure of said patient in said region, the matrix holding a corresponding location and data value for each data element;

b) analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) using a plurality of the boundary data elements to form an implant boundary;

d) establishing a measurement boundary which conforms to said implant boundary and is translated from said implant boundary by a predetermined distance along a translation axis;

e) calculating bone mineral density for the data values located between the implant boundary and the measurement boundary and displaced along the implant boundary to produce a set of segment values corresponding to the density of the bone adjacent to the implant;

f) averaging the segment values to obtain a value representing average bone mineral density adjacent the implant; and

g) displaying on said visual display a visual representation of the result of step f).

7. A method of using a dual energy densitometer having a visual display to determine bone mineral density in a patient having a bone with a prosthetic implant, the method comprising the steps of:

a) scanning with said dual energy densitometer said patient in the region of said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said bone and implant at a defined location in the internal structure of said patient in said region, the matrix holding a corresponding location and data value for each data element;

b) analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) using a plurality of the boundary data elements to form an implant boundary;

d) employing the implant boundary to isolate and remove from the determination of bone mineral density data elements resulting from energy absorbed by said implant;

e) employing the implant boundary to identify those data elements which result from energy absorbed by bone immediately adjacent said implant;

f) displaying on said visual display a visual representation of said matrix showing said implant and said bone adjacent said implant;

g) analyzing the data elements identified in step e) to determine bone mineral density of said bone adjacent said implant; and

h) displaying the result of step g) on said visual display.

8. A method as claimed in claim 7 further including a step for identifying within said matrix a fiducial point of the bone and referencing the data elements analyzed in step g) to said fiducial point.

9. A method of using a dual energy densitometer having a visual display to determine bone mineral density in a patient having a bone with a prosthetic implant, comprising the steps of:

a) scanning with said dual energy densitometer said patient in the region of said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said bone and implant at a defined location in the internal structure of said patient in said region, the matrix holding a corresponding location and data value for each data element;

b) analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) using a plurality of the boundary data elements to form an implant boundary;

d) locating at least one region of interest, said region of interest containing only bone data elements and having one side adjacent said implant boundary, said one side conforming to the shape of said adjacent implant boundary;

e) displaying on said visual display a visual representation of said bone, said implant and said region of interest;

f) analyzing said bone data elements within said region of interest to calculate bone mineral density within said region of interest; and

g) displaying on said visual representation of said calculated bone mineral density corresponding to the bone mineral density of bone adjacent said implant in said region of interest.

10. The method as claimed in claim 9 further including the step of establishing at least one landmark on said edge boundary and using said landmark to locate at least one said region of interest.

11. A method of using a dual energy densitometer having a visual display to monitor change in bone density in bone adjacent a prosthetic implant, said method comprising the steps of:

a) scanning with said dual energy densitometer said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said bone and implant at a defined location in the internal structure of said patient in said region, the matrix holding a corresponding location and data value for each data element;

b) analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) using a plurality of the boundary data elements to form a first and second implant boundary generally opposed about an axis of the implant;

d) employing the first and second implant boundaries to isolate data elements associated with the implant from said other data elements so that said implant data elements are removed from the determination of bone mineral density;

e) analyzing said other data elements to identify bone data elements which result from energy absorbed by said bone;

f) defining a medial and lateral edge boundary between said bone data elements and non-bone data elements of said other data elements;

g) establishing at least one landmark on said edge boundary;

h) using said landmark to locate at least two regions of interest, one region of interest on the medial side of said implant and the other region of interest on the lateral side of said implant, each said region of interest containing only bone data elements and each said region of interest having one side adjacent said implant boundary, each said one side conforming to the shape of one implant boundary;

i) analyzing said bone data elements within each said region of interest to calculate bone mineral density within each said region of interest;

j) displaying on said visual display a comparison of said calculated bone mineral density for each said region of interest corresponding to the bone mineral density of bone adjacent said implant in each said region of interest; and

k) repeating on a subsequent date steps a) through j) so as to determine the change in bone mineral density in each said region of interest with time.

12. A dual energy densitometer for determining bone mineral density in a patient having a bone with a prosthetic implant, comprising:

a) a means to scan said patient with said densitometer in the region of said bone and said implant so as to generate a two dimensional matrix of data elements wherein the value of each said data element of said matrix is proportional to the absorption of energy by said implant and bone at a defined location in the internal structure of said patient in said region, the matrix holding a corresponding location and data value for each data element;

b) means for analyzing the matrix of data elements to identify a data element as a boundary data element, the boundary data element being on an edge of said implant adjacent to a portion of the bone of the patient, the location of said boundary data element being a function of a value and location of the boundary data element and a value and location of at least one immediately adjacent data element;

c) means using a plurality of the boundary data elements for forming an implant boundary;

d) means using the implant boundary to distinguish within said matrix, data elements which result from the absorption of energy by said bone from data elements which result from the absorption of the implant;

e) a means to establish at least one region of interest, said one region of interest containing only bone data elements resulting from energy absorbed by bone immediately adjacent said implant boundary;

f) a means to visually display said matrix so that the region of the matrix containing implant data elements is highlighted and conforms to the shape of said implant, and so that said value of each said bone data element is converted to an intensity of light such that the intensity of light is proportional to the absorption of energy by said bone, and so that the region of matrix containing bone data elements conforms to the shape of said bone, and so that at least one region of interest is able to be identified;

g) a means to analyze bone data elements in said one region of interest so as to determine bone mineral density;

h) a means to visually display a representation of bone mineral density in said one region of interest.