Feasibility study comparing synthesized mammography with digital breast tomosynthesis and digital mammography for simulated first round screening in a single BreastScreen NSW centre.

INTRODUCTION: While digital breast tomosynthesis (DBT) has proven to enhance cancer detection and reduce recall rates (RR), its integration into BreastScreen Australia for screening has been limited, in part due to perceived cost implications. This study aims to assess the cost effectiveness of digital mammography (DM) compared with synthesized mammography and DBT (SM + DBT) in a first round screening context for short-term outcomes. METHODS: Clients recalled for nonspecific density (NSD) as a single lesion by both readers at the Northern Sydney Central Coast BreastScreen service in 2019 were included. Prior images were excluded to simulate first-round screening. Eleven radiologists read DM and synthesized mammography with DBT (SM + DBT) images 4 weeks apart. Recall rates (RR), reading time, and diagnostic parameters were measured, and costs for screen reading and assessment were calculated. RESULT: Among 65 clients studied, 13 were diagnosed with cancer, with concordant cancer recalls. SM + DBT reduced recall rates (RR), increased reading time, maintained cancer detection sensitivity, and significantly improved other diagnostic parameters, particularly false positive rates. Benign biopsy recalls remained equivalent. While SM + DBT screen reading cost was significantly higher than DM (DM AU$890 ± 186 vs SM + DBT AU$1279 ± 265; P < 0.001), the assessment cost (DM AU$29,504 ± 9427 vs SM + DBT AU$18,021 ± 5606; P < 0.001), and combined screen reading and assessment costs were significantly lower (DM AU$30,394 ± 9508 vs SM + DBT AU$19,300 ± 5721; P = 0.001). SM + DBT screen reading and assessment of 65 patients resulted in noteworthy cost savings (AU$11,094), equivalent to assessing 12 additional clients. CONCLUSION: In first round screening, DBT yields significant cost savings by effectively reducing unnecessary recalls to assessment while maintaining diagnostic efficacy.

The utility of cross-sectional imaging in the management of suspected scaphoid fractures.

INTRODUCTION: Scaphoid fractures are the commonest carpal bone fracture. If untreated they pose significant risk to patients, thus if a scaphoid fracture is suspected, patients are managed with immobilisation. Although scaphoid fractures may be difficult to diagnose on plain radiography, sometimes for months after injury, ongoing radiographic surveillance is preferred due to its low upfront cost. Patients in immobilising casts for long periods experience significant personal and social ramifications such as difficulty working and self-caring. This study examines whether cross-sectional imaging by computed tomography (CT) or magnetic resonance imaging (MRI) is quicker than serial X-ray surveillance at allowing a scaphoid fracture to be either excluded or confirmed. METHODS: A retrospective record review was performed of the 1709 patients who presented to Royal North Shore Hospital in 2015 with wrist injuries, finding 104 patients clinically suspicious for a fractured scaphoid. RESULTS: All patients were examined by X-ray during their initial hospital presentation, providing 33.7% of final diagnoses in 0.6 ± 1.7 days. However, if initial X-ray proved inconclusive, subsequent serial X-ray surveillance made a final diagnosis after a mean of 24.1 ± 17.2 days, with some being immobilised for up to 67 days before diagnosis. Cross-sectional imaging significantly reduced diagnosis time to 9.8 ± 5.8 days (P = 0.0016), with a maximum immobilisation time of 24 days. CONCLUSION: Cross-sectional imaging allows for faster scaphoid fracture diagnosis than X-ray. We propose a protocol for scaphoid fracture diagnosis wherein patients undergo two episodes of X-ray separated by 7 days, followed by a single MRI if clinical suspicion remains, minimising unnecessary immobilisation.

Comparative analysis of 2 glenoid version measurement methods in variable axial slices on 3-dimensionally reconstructed computed tomography scans.

BACKGROUND: Most glenoid version measurement methods have been validated on 3-dimensionally corrected axial computed tomography (CT) slices at the mid glenoid. Variability of the vault according to slice height and angulation has not yet been studied and is crucial for proper surgical implant positioning. The aim of this study was to analyze the variation of the glenoid vault compared with the Friedman angle according to different CT slice heights and angulations. The hypothesis was that the Friedman angle would show less variability. MATERIALS AND METHODS: Sixty shoulder CT scans were retrieved from a hospital imaging database and were reconstructed in the plane of the scapula. Seven axial slices of different heights and coronal angulations were selected, and measurements were carried out by 3 observers. RESULTS: Mid-glenoid mean version was -8.0° (±4.9°; range, -19.6° to +7.0°) and -2.1° (±4.7°; range, -13.0° to +10.3°) using the vault method and Friedman angle, respectively. For both methods, decreasing slice height or angulation did not significantly alter version. Increasing slice height or angulation significantly increased anteversion for the vault method (P < .001). Both interobserver reliability and intraobserver reliability were significantly higher using the Friedman angle. CONCLUSION: Version at the mid and lower glenoid is similar using either method. The vault method shows less reliability and more variability according to slice height or angulation. Yet, as it significantly differs from the Friedman angle, it should still be used in situations where maximum bone purchase is sought with glenoid implants. For any other situation, the Friedman angle remains the method of choice.

Evaluating the role of magnetic resonance imaging post-neoadjuvant therapy for breast cancer in the NEONAB trial.

BACKGROUND: Magnetic resonance imaging (MRI) accuracy after neoadjuvant systemic therapy (NST) for breast cancer varies according to hormone receptor (HR), human epidermal growth factor receptor type-2 (HER2) subtype and Ki-67 proliferation index. Whether MRI accuracy varies by genomic signatures is unknown. We examined the accuracy of MRI in the NEONAB trial (Clinicaltrials.gov #: NCT01830244). AIM: To examine the accuracy of MRI to predict pathological response to neoadjuvant therapy for breast cancer in the NEONAB trial. METHODS: Patients with stages II-III breast cancer received sequential epirubicin, cyclophosphamide and nab-paclitaxel and trastuzumab if they were HER2+. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated to assess the utility of preoperative MRI to predict pathological complete response (pCR). Bland-Altman plots were used to assess agreement between MRI and pathological assessment of residual disease. RESULTS: MRI correctly predicted pCR in 64.1% of the cohort. Sensitivity and specificity were 52% and 78%, respectively; PPV 73% and NPV 58%. MRI predicted pCR most accurately in HER2-positive patients; sensitivity 58%, specificity 100%, PPV 100% and NPV 38%. MRI had higher PPV and NPV in tumours with Ki-67 ≥ 15% than tumours with Ki-67 < 15%, 75% versus 50% and 57.5% versus 50%, respectively. In this study, MRI underestimated residual tumour size by 1.65 mm (limits of agreement: 43.07-39.77 mm). CONCLUSIONS: MRI appears more accurate for predicting pCR in HER2+ disease than other subtypes and in cancers with Ki-67 ≥ 15% compared to those with Ki-67 < 15%. Accuracy of MRI in our HR+, RS ≥ 25 cohort is comparable to previous reports of unselected HR+ disease. MRI post-NST should be interpreted in conjunction with HER2 status and Ki-67 index of the primary.

Multifocal low-grade central osteosarcoma: a rare case.

Low-grade central osteosarcoma (LGCOS) is a rare variant of osteosarcoma. We present a rare case of multifocal LGCOS located in two distinct skeletal sites, initially noted as incidental findings on imaging for distant traumatic pathology. Both sites seemed small and innocuous on initial imaging, and were quiescent clinically, illustrating the value of close interval multimodal surveillance scanning.

Lack of agreement between computer navigation and post-operative 2-dimensional computed tomography (CT) measurements for component and limb alignment in total knee arthroplasty (TKA).

BACKGROUND: The purpose of this study was to assess the degree of mismatch between intraoperative navigation data using imageless computer navigation and post-operative CT scan measurements with respect to bone cuts, component and limb alignment during TKA. METHODS: Intraoperative navigation data including bone cut verification and overall limb alignment during TKA was compared to postoperative CT measurements of component and limb alignment according to the Perth protocol. The proportion of cases with mismatch between navigation and CT measurements at two and three degree thresholds was identified. RESULTS: In a total sample of 50 primary TKAs, 20% of cases showed a mismatch of more than two degrees between navigation and CT obtained measurements for coronal femoral alignment, 42% for femoral rotation, 16% for tibial component coronal alignment and 32% for overall limb alignment. CONCLUSION: Mismatch between intraoperative navigation data and postoperative CT measurements suggests that postoperative CT scan alignment data should be interpreted with caution. A surgeon should consider a multitude of factors when analysing component and limb alignment postoperatively.

Pubic apophysitis: a previously undescribed clinical entity of groin pain in athletes.

BACKGROUND: Sport-related pubalgia is often a diagnostic challenge in elite athletes. While scientific attention has focused on adults, there is little data on adolescents. Cadaveric and imaging studies identify a secondary ossification centre located along the anteromedial corner of pubis beneath the insertions of symphysial joint capsule and adductor longus tendon. Little is known about this apophysis and its response to chronic stress. AIM: We report pubic apophysitis as a clinically relevant entity in adolescent athletes. METHODS: The clinical and imaging findings in 26 highly trained adolescent football players (15.6 years ± 1.3) who complained of adductor-related groin pain were reviewed. The imaging features (X-ray 26/26, US 9/26, MRI 11/26, CT 7/26) of the pubic apophyses in this symptomatic group were compared against those of a comparison group of 31 male patients (age range 9-30 years) with no known history of groin pain or pelvic trauma, who underwent pelvic CT scans for unrelated medical reasons. RESULTS: All symptomatic subjects presented with similar history and physical findings. The CT scans of these patients demonstrated open pubic apophyses with stress-related physeal changes (widening, asymmetry and small rounded cyst-like expansions) that were not observed in the comparison group. No comparison subject demonstrated apophyseal maturity before 21 years of age, and immaturity was seen up to the age of 26 years. CONCLUSIONS: This retrospective case series identifies pubic apophyseal stress (or 'apophysitis') as an important differential consideration in the adolescent athlete who presents with groin pain.

Evaluation of the effect of zoom function on lesion detection by soft-copy reading of screening mammograms.

INTRODUCTION: This study aims to evaluate the effectiveness of zooming in improving screen-reader performance in reporting digital mammograms. METHOD: Two experiments were conducted. In the first experiment, 5 readers were asked to report 59 two-view bilateral mammograms retrospectively with zooming function turned off. The second session was similar to the first one except that zooming was enabled. The task of readers was to assess if the mammograms were normal or abnormal and rate the confidence levels for each of the lesion they detected. The reader performances were evaluated via case sensitivity, lesion sensitivity, specificity, receiver operating characteristics (ROC) area under the curve (AUC) and jackknife free-response receiver operating characteristics (JAFROC) figure of merit (FOM). RESULTS: There was no significant improvement in overall reader performance in detecting abnormalities in zooming condition compared with no zooming in terms of case sensitivity (96% and 87%, P = 0.285) or lesion sensitivity (88% and 81%, P = 0.224). However, differences in ROC AUC and JAFROC FOM (P ≤ 0.05) were found in two readers when they performed the test set with zooming function. CONCLUSION: The results suggested that the use of the zooming function did improve the performance of some readers in detecting abnormal cases.

Colletotrichum gloeosporioides sensu lato causing deep soft tissue mycosis following a penetrating injury.

Colletotrichum species have been rarely implicated in human disease. We describe a case of deep soft tissue mycosis following a penetrating injury with a lemon tree thorn. Direct Blankophor BA (Bayer) stain from intraoperative tissue showed fungal elements. Pure growth fungus was apparent at 2-4 days. Morphological features provisionally identified the isolate as a coelomycetous fungus, likely Colletotrichum species. This was confirmed with molecular analysis of the internal transcribed spacer region (ITS) region.

Osteoarthritis: what does imaging tell us about its etiology?

Osteoarthritis (OA) is the most common joint disorder and a leading cause of disability. Due to an aging population and increasing obesity, the incidence of OA is rising. The etiology of OA is multifactorial and complex; thus prevention of OA remains challenging. Risk factors can be divided into person-level factors such as age, sex, obesity, genetics, race/ethnicity, and diet, and joint-level factors including injury, malalignment, and abnormal loading of the joints. This review provides a brief overview of the person-level risk factors and a more in-depth analysis of those at the joint level. It is only through an improved understanding of risk factors for the disease that we may be able to intervene meaningfully and prevent its occurrence.

Articular cartilage changes in patients with osteoarthritis after osteotomy.

BACKGROUND: High tibial osteotomy (HTO) is a method used to treat medial compartmental osteoarthritis in the knee. The realignment of the knee changes the loading patterns within the joint and may allow for regeneration of articular cartilage. Magnetic resonance imaging methods can be used to assess the quality of the regenerated cartilage. HYPOTHESIS: Altering mechanical alignment through HTO will have predictable effects on articular cartilage, allowing cartilage preservation and possible regeneration. Quality of regenerated cartilage will be inferior to normal articular cartilage. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Ten patients undergoing medial opening wedge HTO were evaluated using dGEMRIC methods (ie, delayed gadolinium-enhanced magnetic resonance imaging of cartilage) preoperatively and at 6 months, 1 year, and 2 years after HTO. Magnetic resonance images were evaluated by hand segmentation, and T1(Gd) relaxation times reflective of glycosaminoglycan content were determined for these regions of interest using magnetic resonance imaging analysis software. RESULTS: The lateral compartment displayed higher T1(Gd) values than the medial compartment at baseline. Initially, a decrease in T1(Gd) values on the medial side were observed for all patients at 6 months and remained reduced for all but 2 participants at 1 year and 2 years after HTO. However, on the medial side after 6 months, the rate of change for T1(Gd) values shifted from being negative (-9.6 milliseconds per month) to being positive (1.7 milliseconds per month). A positive change in the T1(Gd) of the medial tibial plateau was responsible for the positive overall change in the medial compartment. There was no significant difference in the rate of change on the lateral side (P = .141), with the average over the 2-year period being a decrease of 2.28 milliseconds per month. CONCLUSION: Medial opening wedge HTO provides subjective improvements in pain and quality of life, but the potential benefit of allowing articular cartilage preservation and possible regeneration is not well established. Results showed that after a nonweightbearing period, the rate of change in the medial compartment changes from negative to positive, indicating the potential for articular cartilage recovery secondary to an improved mechanical environment.

Application of imaging guidelines in patients with suspected cervical spine trauma: retrospective analysis and literature review.

Safe and efficient clearance of cervical spine injury in blunt trauma patients has been a controversial topic among health professionals. The increased availability of CT scanners in major trauma centers seems to be a factor that has led to increased number of unnecessary cervical spine imaging using this imaging modality. The objective of this study was to investigate the applicability and efficacy of a pre-test clinical criterion in order to stratify post-blunt trauma victims based on their risk of sustaining cervical spine injury and in turn recommend an appropriate imaging modality accordingly. Goergen's criteria (Australas Radiol 48(3):287, 2004), a pre-investigation diagnostic algorithm was retrospectively applied to 106 blunt trauma victims who presented to a level 1 trauma center in Sydney, Australia, and had a CT scan of cervical spine as part of their initial management. Overall, nine (8.5%) of patients sustained a significant cervical spine injury. All nine patients would be classified as high-risk victims according to the algorithm investigated in this study, warranting CT scanning. No patients with low-risk injuries were demonstrated to have a significant cervical spine injury. There was a statistically significant greater proportion of acute cervical spine injuries detected in the high-risk group (p value = 0.0024). Hence, using Goergen's diagnostic algorithm could reduce the number of unnecessary cervical spine CT scans ordered, while not compromising the quality of care in post-blunt trauma victims.

Pictorial review: 'fishtail deformity' of the elbow.

Fishtail deformity of the elbow is characterised by a contour abnormality of the distal humerus, which develops when the lateral trochlear ossification centres fails to develop or resorbs. It is an uncommon complication usually following a distal humeral fracture in childhood. Whilst initially presumed to be a benign condition, long-term follow-up suggests that patients with fishtail deformity are prone to functional impairment, ongoing pain and the development of early osteoarthrosis. This paper reviews the imaging findings in fishtail deformity, the proposed aetiology and the potential long-term complications.

Overuse and traumatic injuries of the elbow.

MR imaging is a useful modality for evaluating athletes presenting with elbow pain. Osteochondral injuries and ligamentous injuries are well seen on MR imaging. Ligamentous injuries may be associated with clinical instability syndromes, the secondary signs of which may be evident on MR images. Enthesopathies and distal biceps tendon injuries are common clinical problems that may be seen in both professional and recreational athletes. Nerve compression syndromes may be investigated using MR imaging; however, the usual aim of imaging is to exclude an underlying space-occupying lesion. This article reviews the basic anatomy of the elbow joint and discusses the common osteochondral injuries, ligamentous injuries, instability syndromes, and tendinous pathologies at the elbow joint. The role of imaging in compressive neuropathies is briefly discussed.

Cartilage defects are associated with physical disability in obese adults.

OBJECTIVE: To describe the associations between physical disability measures and knee cartilage defects in obese adults. METHODS: One hundred and eleven obese subjects were recruited from laparoscopic adjustable gastric banding or exercise/diet weight loss programmes. All subjects completed disease-specific (WOMAC) and general health status (SF-36) questionnaires, and were assessed for range of knee motion, tibiofemoral alignment and quadriceps strength. Knee cartilage defects were graded on MRI according to established protocol. Regression analysis was adjusted for age, gender, BMI and presence of clinical knee OA. RESULTS: The association between higher whole compartment cartilage defect scores and increasing BMI, age and clinical knee OA was confirmed in this obese cohort (r = 0.27, P = 0.01; r = 0.26, P = 0.007; P < 0.0001, respectively), whereas new associations were found with reduced knee range of motion (r = 0.5, P < 0.0001). No associations were found between defect scores and quadriceps strength. Varus malalignment was associated with higher medial cartilage defect scores (r = 0.33, P = 0.013). Higher levels of pain, stiffness and physical disability (WOMAC, SF-36) were associated with higher medial compartment and patella cartilage defect scores. CONCLUSIONS: Knee cartilage defects increase with increasing obesity and are associated with both objective and self-reported measures of physical disability. Longitudinal studies are required to assess the potential for change or improvement in cartilage defects with weight loss.

The accuracy of magnetic resonance imaging scanning and its influence on management decisions in knee surgery.

PURPOSE: The purpose of our study was to evaluate the impact of preoperative magnetic resonance imaging (MRI) assessment of articular knee pathology on the clinical management of patients presenting with joint line pain. METHODS: A preliminary study on 100 patients was performed to assess the accuracy of specific MRI sequences, using arthroscopy as a gold standard. Six hundred and eighteen consecutive patients with knee symptoms presenting to 2 specialist knee surgeons were then recruited. A clinical diagnosis of an arthroscopically treatable lesion was made in all cases. Clinical assessment data were correlated to subsequent MRI findings, recording any discrepancy and in particular whether or not MRI findings influenced management decisions. RESULTS: In the preliminary study, MRI sequences had an overall sensitivity of 83.2% and a specificity of 94.3% for the detection of chondral lesions. However, when considering arthroscopic grade III and IV lesions, MRI sensitivity and specificity were improved to 84.5% and 97.1%. In the second phase of the study, 141 (22.8%) of the 618 patients presenting with knee symptoms had an altered clinical management subsequent to MRI. The presence of unexpected chondral lesions was found in 77 of these patients. Conversely, 22 patients with clinical symptoms suspicious for simple chondral degeneration had unstable meniscal tears. CONCLUSIONS: We suggest that preoperative MRI scanning identifies a group of patients who have more advanced degenerative joint disease than the clinical assessment and the plain radiographs suggest. This would expedite definitive surgery in patients with advanced osteoarthritis on MRI scans. LEVEL OF EVIDENCE: Level II, development of diagnostic criteria on basis of consecutive patients with universally applied gold standard.

Delayed gadolinium-enhanced magnetic resonance imaging of cartilage: clinical associations in obese adults.

OBJECTIVE: Delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC) is used to assess cartilage glycosaminoglycan distribution. Our aim was to determine the relationships between self-reported pain and disability, clinical variables, and serum leptin, and dGEMRIC indices in obese subjects with and without clinical knee osteoarthritis (OA). METHODS: Seventy-seven subjects were recruited from laparoscopic adjustable gastric banding or exercise and diet-weight loss programs. The dGEMRIC index was assessed on MRI according to established protocol. Regression analysis adjusted for age, sex, body mass index (BMI), and presence of clinical knee OA. RESULTS: Mean age and BMI were 51 +/- 12.7 years and 39.6 +/- 6.2 kg/m(2). Twenty-three subjects (30%) had clinical knee OA (American College of Rheumatology criteria). The medial and lateral dGEMRIC indices were 538 +/- 80 ms and 539 +/- 86 ms. Age correlated negatively with medial (r = -0.40, p < 0.001) and lateral (r = -0.29, p = 0.012) dGEMRIC index. Subjects with clinical knee OA had significantly lower medial dGEMRIC index; however, no association was found for BMI. Varus alignment correlated with lower medial dGEMRIC index (r = -0.43, p < 0.006), while quadriceps strength correlated positively with lateral dGEMRIC index (r = 0.32, p = 0.008). There was also a negative correlation between serum leptin and lateral dGEMRIC index in women (r = -0.39, p = 0.035), with a trend in men (r = -0.52, p = 0.08). There were weak associations with physical disability, as self-reported on the WOMAC questionnaire. CONCLUSION: In obese subjects, knee dGEMRIC index was associated with age, clinical knee OA, abnormal tibiofemoral alignment, and quadriceps strength. Longitudinal studies are required to assess the potential for improvement in dGEMRIC index with interventions such as strength training.

Bone bruises associated with ACL rupture: correlation with injury mechanism.

BACKGROUND: Different patterns of bone bruising are seen on magnetic resonance imaging in acute anterior cruciate ligament ruptures. These patterns may relate to the mechanism of injury. HYPOTHESIS: There is a correlation between the mechanism of anterior cruciate ligament injury and bone bruise patterns on magnetic resonance imaging. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Data regarding the mechanism of anterior cruciate ligament rupture were collected prospectively on patients who had anterior cruciate ligament reconstructions. Inclusion criteria included a clear history of mechanism, magnetic resonance imaging within 6 weeks of injury, and no previous knee injury. Patients were divided into noncontact and contact mechanism groups. Bone bruise frequency, location, depth, and intensity were analyzed using magnetic resonance imaging and correlated with the mechanism of injury. RESULTS: Two hundred fifty-six patients were identified; 100 met the inclusion criteria, 86 were in the noncontact mechanism group, and 14 were in the contact mechanism group. The proportion of bone bruises in the lateral compartment in both groups was higher (P < .001) than in the medial compartment. Bone bruising was more frequent, deeper, and more intense in the noncontact group, with frequency (P = .019) and intensity (P < .001) scores reaching significance at the lateral tibial plateau. Medial compartment bone bruising was seen more frequently than previously reported, particularly in the noncontact group. CONCLUSION: The noncontact mechanism appears to cause more severe bone bruising in both the medial and lateral compartments.

Reliability of bony landmarks for restoration of the joint line in revision knee arthroplasty.

The aim of this study was to determine the reliability of bone landmarks for restoring the joint line in revision knee arthroplasty. The relationship of the femoral epicondyles, the tibial tubercle (TT) and the fibular head (FH) to the joint line was measured on 200 magnetic resonance imaging (MRI, 100 females, 100 males), including assessment on intraobserver and interobserver reliability. MRI scans demonstrating chondral lesions and osteoarthritis were excluded, as were patients with immature skeletons or a history of previous knee surgery. Sequences in sagittal, coronal and axial planes were used as well as cross-referencing with the same computer software. In order to account for size differences between patients, each bony landmark measurement was converted to a ratio relative to the femoral or/and tibial width. We found a transepicondylar axis equal to 3.11 degrees (+/-1.9). The average distance from the epicondyles to the joint line was respectively 23 mm on the lateral side and 28 mm on the medial side. However there was a variation of distance from the epicondyles of the joint line up to 11 mm and a significative difference was found between male and female. We determined the distances from the tip of the FH and from the TT to the joint line. The joint line-FH distance averaged 14 mm (range 4.1-22.13) with no gender difference. The joint line-TT distance was averaged 22 mm (range 10.61-32.09). We determined an epicondylar ratio (distance from the lateral epicondyle to the joint line related to the femoral width). We found this ratio averaged 28% with no gender difference (P = 0.09). There is a large variation of bony landmarks depending on the size of the individual. Considering this findings, the FH is not a reliable guide for the joint line in revision surgery. Previous studies have measured the absolute values from various landmarks to the joint line. This study provides a significant advantage, in that the level of the joint line can be determined for each individual by using a ratio to account for gender and size differences.