[Oradlist] Bone dentisty measurement with CBCT : How Reliable?

[Allan G Farman]

A statement was made that went unquestioned; namely the necessity of implant dentists to know with precision bone density. I would like to hear of article that provide strong evidence that this is indeed the case. What is the relationship between jawbone density and implant success or failure? Second, I seem to remember that not all multislice CT scanners are well calibrated for precision in determining Hounsfield units. I would be obliged if anyone could provide references concerning this issue as well. AGF



Allan G. Farman, BDS, PhD, MBA, DSc, Diplomate ABOMR

Prof. Radiology & Imaging Science
Univ. Louisville School of Dentistry: SUHD
501 South Preston Street,
Louisville, Kentucky 40292, USA 

Tel: +1(502) 852.1241
Fax: +1(502)852.1626


>>> "Benn, Douglas K." <DouglasBenn at creighton.du> 05/17/2009 12:43 PM >>>
I have no experience with CBCT regarding density measurements. However, I wonder if a jaw shaped step-wedge placed into the occlusal region could provide a good reference? You will still have issues such as beam hardening from jaw bone but this could be allowed for when calculating density.

Dr Douglas K Benn, BDS, M.Phil., Ph.D., Dipl. Dental Radiology (Royal College of Radiologists, England).
Professor
Dept of General Dentistry
Creighton University Dental School
2500 California Plaza
Omaha
Nebraska 68178

Tel: (402)280 5025
Fax: (402)280 5094



-----Original Message-----
From: oradlist-bounces at lists.ucla.edu on behalf of Mohamed Elrufaei
Sent: Sun 5/17/2009 9:58 AM
To: oradlist at lists.ucla.edu 
Subject: [Oradlist] Bone dentisty measurement with CBCT : How Reliable?
 
Dear Oradlisters,



The attached abstract was published in April's Issue of OOOE, the authors
suggest "*it may be necessary to use calibration phantoms that are scanned
simultaneously with the patient to allow for accurate determination of bone
density**"*



Do you have an opinion on this issue? do you still think CBCT can produce a
reliable measurement of bone density (D1, D2, D3, D4)? A major issue at
least for implantologists



The authors note *a marked change* in grayscale values (bone density)
readings *on changing the FOV*!!



Kind regards



Dr. Mohamed I Elrufaei

KSMC "Riyadh Dental Center"

Saudi Arabia

* *

* *

* *

*CORRELATION OF CBCT GRAY SCALE VALUES WITH*

*BONE DENSITIES*

* *

* **Haristoy RA, Valiyaparambil JV, Mallya*

*SM, Section of Oral and Maxillofacial Radiology, University*

*of Connecticut School of Dental Medicine, Farmington CT*

* *

*Introduction: *Cone beam CT (CBCT) units allow for determination

of gray scale values of pixels within the image. However,

unlike with Hounsfield Units, there is no standard for

scaling these gray-scale values to attenuation coefficients of

tissues. Variations of the gray scales with exposure parameters

(kVp, mAs and field of view) are not known. Additionally, the

relationship between the gray values and bone densities are not

known.

* *

*Objectives: *The purpose of this study was to determine the

influence of exposure parameters on the gray-scale values of a

CBCT unit.

* *

*Materials and Methods: *We fabricated a radiographic phantom

consisting of varying concentrations of dipotassium hydrogen

phosphate (K2HPO4, 50 - 1000 mg/ml). K2HPO4 solutions

are bone equivalent and, thus, were used to simulate bone densities

of trabecular and cortical bone. The phantom was imaged

on a CB Mercuray unit at various exposure parameters. Grayscale

values were determined using 2 software programs-Image

J and Osirix. Gray-scale values were normalized to the gray-scale

value of water. The influence of the various exposure parameters

to normalized, gray-scale values was determined.

* *

*Results: *At all exposure settings examined, there was a

strong correlation between gray-scale values and bone density

over the entire range of bone densities examined (R2_0.99).

Both software programs yielded similar results-measured grayscale

values were not significantly different between the 2 programs.

However, at a given kVp-mAs setting, the normalized grayscale

values varied between the different fields of view- smaller

fields of view yielded higher gray-scale values for the same

concentration of bone-equivalent material. This variance ranged

from 10% at lower (trabecular-bone equivalent) densities to 15%

at higher (cortical bone equivalent) densities.

* *

*Discussion: *Our results demonstrate a strong correlation

between gray-scale values on CBCT images and bone densities.

This has implications for potential quantitative radiological approaches

to determine bone density from CBCT images. However,

given the variation of the gray-scale values, despite normalization,

it may be necessary to use calibration phantoms that

are scanned simultaneously with the patient to allow for accurate

determination of bone density.