A 3D radiological study of age-related quantitative and morphological differences in the human femur: clinical and anthropological applications

© 2010 Dr. Jacqueline Lee Hislop-JambrichThe establishment of a valid scientific instrument for the non-destructive analysis of age-related change in the human femur is essential for the disciplines of clinical medicine and anthropology. The overall aim of this thesis was therefore to develop novel and scientifically verifiable methods for using multiple detector-row computed tomographic (MDCT) data to produce a population-based, morphometric and densitometric record of age-related differences in human femoral bone. The resulting study of contemporary urban Australians is the first to use MDCT data to produce a contemporary model of age-related differences of the human femur. Four independent empirical studies were performed, each of which established the validity of the mortuary-sourced MDCT data, and then reported the age-related radiological findings. The adult population used for this work was taken from the high-resolution MDCT scans performed routinely at the Victorian Institute of Forensic Medicine (VIFM) in Melbourne Victoria Australia. The scans were therefore from those who died unexpectedly in the state of Victoria, and who had no disease or pathology involving the femur. The first study engaged clinical quantitative computed tomography (QCT) software to create a model of the bilateral three-dimensional (3D) densitometric characteristics of the population. The hypothesis was that clinical software may be used effectively on mortuary-based MDCT data to derive population-based assessments of quantitative bone characteristics. Aspects of reproducibility, quality assurance and calibration were all extensively investigated. Clinical ionising-radiation dose estimation software was also used to compare the effective dose delivered during the mortuary MDCT acquisition, to what may be expected in implementing a similar protocol on the living. Results established that a non-destructive QCT technique may be effectively employed using mortuary MDCT data for the purposes of an adult population-based analysis. Results also demonstrated significant differences in gender and age-based expressions of bone mineral and spatial QCT characteristics. Ionising radiation dose calculations showed little variance between the VIFM and theorised clinical protocols. The second study used those same MDCT data to produce 3D image-renders of the bilateral femora. The hypothesis was that there were predictable morphologic age, gender and symmetry related differences within a contemporary predominantly urban adult population spanning 80 years. A series of novel and adapted caliper-type measurements, designed to evaluate age-related differences were implemented. Results were then compared in terms of the physical features of the individuals, such as weight, height and age. A study of femoral symmetry was also completed. Results demonstrated large variability of symmetry in individuals and of deep and surface morphometry across the group generally. Results also demonstrated that irrespective of age, all morphological variables tested were discriminating for gender. The third study used results from an analysis of 17 right-sided femoral specimens from the Melbourne Femur Collection (MFC), to assess the impact of three different MDCT scanning conditions on spatial and quantitative measurements of bone. The hypothesis was that alterations in the scanning conditions and environment would produce little change in the spatial assessments, and consistent variation for the quantitative evaluations. Results demonstrated a strong and predictable correlation in all scanning conditions for both spatial and quantitative assessments. The fourth study produced an epidemiological review of all hip fractures in bodies admitted to the VIFM for autopsy in 2008, as well as a QCT and morphometric assessment from 14 unilateral hip fracture cases. The hypothesis was that the fracture cases would present with dissimilar QCT and morphometric assessments as the normal or un-fractured control group from the first two research chapters. While results demonstrated no difference in morphometric features between the fractured and normal groups, there were significant differences (p<0.005) for BMD, bone mass and cortical depth variables. The findings indicate a high sensitivity of these 3D variables for the determination of relative risk of femoral neck fracture. The cortical depth comparison also demonstrated that there were definite “safe” and “unsafe” levels expressed in this variable, in terms of low and high probability of femoral neck fracture. This high-level distinction is not currently available clinically using 2D bone assessments. Assessing individual biological-age from the femora after they have reached skeletal maturity has previously been recognised as problematic. Results from this study have however demonstrated that it is possible to use non-destructive modified clinical and anthropological techniques on mortuary-based MDCT data to quantify age-related differences in a contemporary urban population of diverse racial backgrounds

A quality audit of MRI knee exams with the implementation of a novel 2-point DIXON sequence

INTRODUCTION: The objective of this study was to evaluate the effect on diagnostic image quality and acquisition time utilising a DIXON sequence to replace two standard proton density (PD) fat saturation (FS) sequences in routine magnetic resonance (MR) evaluation of the knee. METHODS: Thirty-one consecutive patients referred for an MR examination of the knee were examined using the routine departmental protocol along with the addition of a DIXON sequence. The sequences were all evaluated by a senior radiologist and feedback provided via both written and scored responses. The sequences were then repackaged for two additional reviewers with the sagittal PD FS (Chemical Shift Selective Fat Saturation or CHESS) and sagittal PD removed and replaced with the DIXON (fat suppressed and in-phase, respectively) sequence equivalents. Scored and written responses were tabled and reviewed to assess the suitability of sequence replacement. RESULTS: The DIXON-based images were judged as being comparable replacements for the sagittal PD fat sat and PD sequences. There was no report of any loss in diagnostic confidence across the 31 patients (total of 32 knees) with a time saving of just over 10% gained. The most common issues raised affecting image quality, though not affecting diagnostic attributes, were patient motion and a minor chemical shift artefact. CONCLUSION: The use of the DIXON technique in place of the PD sequences was of equivalent diagnostic quality with'good' to 'outstanding' fat suppression observed for the majority of cases using the DIXON sequence with an incremental time saving obtained

Improved dynamic CT angiography visualization by flow territory masking

Backgound and Purpose: Computerized tomography (CT) perfusion (or CTP) source images from CT scanners with small detector widths can be used to create a dynamic CT angiogram (CTA) similar to digital subtraction angiography (DSA). Because CTP studies use a single intravenous injection, all arterial territories enhance simultaneously, and individual arterial territories [i.e., anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA)] cannot be delineated. This limits the ability to assess collateral flow patterns on dynamic CTAs. The aim of this study was to devise and test a postprocessing method to selectively color-label the major arterial territories on dynamic CTA. Materials and Methods: We identified 22 acute-stroke patients who underwent CTP on a 320-slice CT scanner within 6 h from symptom onset. For each case, two investigators independently generated an arterial territory map from CTP bolus arrival maps using a semiautomated method. The volumes of the arterial territories were calculated for each map and the average relative difference between these volumes was calculated for each case as a measure of interrater agreement. Arterial territory maps were superimposed on the dynamic CTA to create a vessel-selective dynamic CTA with color-coding of the main arterial territories. Two experts rated the arterial territory maps and the color-coded CTAs for consistency with expected arterial territories on a 3-point scale (excellent, moderate, poor). Results: Arterial territory maps were generated for all 22 patients. The median difference in arterial territory volumes between investigators was 2.2% [interquartile range (IQR) 0.6-8.5%]. Based on expert review, the arterial territory maps and the vessel-selective dynamic CTAs showed excellent consistency with the expected arterial territories in 18 of 22 patients, moderate consistency in 2 patients, and poor consistency in another 2 patients. Conclusion: Using a novel postprocessing technique, arterial territory maps and dynamic CTAs with vessel-selective color-coding can be derived from a standard CTP scan. These maps may be used to noninvasively assess collateral flow in patients with acute stroke

Defining acute ischemic stroke tissue pathophysiology with whole brain CT perfusion

BACKGROUND: This study aimed to identify and validate whole brain perfusion computed tomography (CTP) thresholds for ischemic core and salvageable penumbra in acute stroke patients and develop a probability based model to increase the accuracy of tissue pathophysiology measurements. METHODS: One hundred and eighty-three patients underwent multimodal stroke CT using a 320-slice scanner within 6hours of acute stroke onset, followed by 24hour MRI that included diffusion weighted imaging (DWI) and dynamic susceptibility weighted perfusion imaging (PWI). Coregistered acute CTP and 24hour DWI was used to identify the optimum single perfusion parameter thresholds to define penumbra (in patients without reperfusion), and ischemic core (in patients with reperfusion), using a pixel based receiver operator curve analysis. Then, these results were used to develop a sigma curve fitted probability based model incorporating multiple perfusion parameter thresholds. RESULTS: For single perfusion thresholds, a time to peak (TTP) of +5seconds best defined the penumbra (area under the curve, AUC 0.79 CI 0.74-0.83) while a cerebral blood flow (CBF) of < 50% best defined the acute ischemic core (AUC 0.73, CI 0.69-0.77). The probability model was more accurate at detecting the ischemic core (AUC 0.80 SD 0.75-0.83) and penumbra (0.85 SD 0.83-0.87) and was significantly closer in volume to the corresponding reference DWI (P=0.031). CONCLUSIONS: Whole brain CTP can accurately identify penumbra and ischemic core using similar thresholds to previously validated 16 or 64 slice CTP. Additionally, a novel probability based model was closer to defining the ischemic core and penumbra than single thresholds