Predictors of in-hospital mortality due to heart failure hospitalisation and trends of guideline-directed medical therapy usage

Background

The burden of heart failure (HF) is immense, from reducing quality of life (QoL) to increasing mortality risks and additional financial implications. The risk of adverse outcomes get higher with each HF hospitalisation (HFH).

Purpose

To look at predictors of in-hospital mortality outcomes during HFH and the prescription trends in conventional guideline-directed medical therapy (GDMT) for HF.

Methods

Retrospective analyses were performed for 7405 HFH cases admitted to our cardiology institution from 2009 to 2018, diagnosed based on the signs and symptoms of heart failure with NTProBNP≥300 at presentation.

Results

Most patients that required HFH were aged <65 years (53.5%), were males (72.8%) and had more diabetes mellitus (66%) and hypertension (75.1%). There were fewer other co-morbidities such as coronary artery disease (CAD) (26.9%), renal insufficiency (33.8%), atrial fibrillation (Afib) (23.9%), dyslipidaemia (40.3%), prior stroke/transient ischaemic attack (TIA) (5.6%), chronic obstructive pulmonary disease (11.6%), current/ex-smokers (45.5%). Most had presenting systolic blood pressure (SBP) >100 mmHg (88.8%), presenting heart rate ≥70 bpm (78.6%) and were in heart failure with reduced ejection fraction (HFrEF) <40% (74.8%). At presentation for HFH, 31.2% had 3 GDMTs (GDMT III) (angiotensin converting enzyme inhibitor / angiotensin receptor blocker / angiotensin receptor neprilysin inhibitor + beta blocker + mineralocorticoid receptor antagonist), 37% had either 2 GDMTs (GDMT II), 25% had only 1 GDMT (GDMT I), while 6.8% had none. The average in-hospital mortality rate was 5.2%. Independent predictors associated with increased in-hospital mortality were males, renal insufficiency, Afib, prior stroke/TIA, SBP ≤100 mmHg, serum sodium <135 mmol/L, uric acid ≥529 μmol/L, NTProBNP ≥6590, inpatient procedures i.e. dialysis, mechanical ventilation and cardiopulmonary resuscitation (CPR). Independent predictors associated with reduced inpatient mortality were hypertension, inpatient cardiac diagnostic procedures and presence of GDMT I, GDMT II and GDMT III at presentation (Figure 1). Throughout the 10 years, the proportion of GDMT prescription were similar; GDMT I (19.1–28.7%), GDMT II (35.1–41.6%), GDMT III (25.2–37.3%). The proportion of GDMT III across the CKD group stages were never more than 50% (Figure 2).

Conclusion

There remains significant in-hospital mortality risk for HFH. While some of these predictors are not modifiable, others are, especially when it comes to GDMT prescriptions. GDMTs provide better prognosis in patients living with HF. There are growing evidence that simultaneous / rapid sequence initiation of GDMTs are more beneficial than the conventional step wise approach. The analysis findings of GDMT proportions at presentation of HFH and also in the CKD group stages meant that many patients are still receiving suboptimal care for their HF and this clinician inertia mentality has got to change.

Funding Acknowledgement

Type of funding sources: None.

Development and validation of gender specific risk models in prediction of mortality for hospitalized heart failure patients in a multiethnic asian population

Funding Acknowledgements

Type of funding sources: None.

Background/Introduction

Heart failure carries substantial morbidity and mortality.  Female has different characteristics compared to male which may affect prognosis and are not represented well in many trials.  Multiple risk scores for in-hospital mortality have been created and validated such as ADHERE (Acute Decompensated Heart Failure National Registry) and GWTG (Get With The Guidelines).  However, these risk scores were in Western population and not gender specific.

Purpose

To develop and validate a gender specific risk model in predicting mortality amongst Asian patients admitted for acute decompensated heart failure (ADHF).

Methods

We analyzed data from our national centre’s ADHF registry.  Epidemiological, clinical, laboratory and imaging variables were ascertained.  Univariate and multivariate analysis using forward stepwise logistic regression were performed to identify predictors for all-cause in hospital mortality with emphasis on disparities between male and female. The accuracy of risk score was assessed using the concordance statistics while calibration was done using the Hosmer-Lemeshow method. The validity of the risk score was determined using separate gender validation cohorts.

Results

A total of 10148 patients admitted for ADHF were analyzed. 8262 patients admitted for ADHF from January 2009 to December 2018 (6008 males and 2254 females) were in the derivation cohort where as 1886 patients (1304 males and 582 females) were selected randomly from January 2019 to July 2021 for our validation cohort.  Female had better survival  (p value =0.04). There were 8 predictive variables for female cohort and 10 predictive variables for male cohort. Similar variables were low systolic blood pressure, loop diuretic use, dialysis, mechanical ventilation and CPR (cardiopulmonary resuscitation).  Interestingly, there were significant differences. For female, other variables that had impact on mortality were hypertension (AOR, 0.23; 95% CI,0.09–0.58), high urea (AOR, 3.32; 95% CI, 1.36–8.09) and hyponatremia (AOR, 2.87, 95% CI, 1.21–6.78).  However for male, the variables were renal insufficiency (AOR, 1.749; 95% CI, 1.13–2.72), history of stroke (AOR, 2.386, 95% CI, 1.22–4.65), LVEF less than 40% (AOR, 2.81; 95% CI, 1.40–5.63), absence of ARB/ACEi (AOR, 2.31; 95% CI, 1.48–3.60) and absence of beta blockers (AOR, 2.65; 95% CI, 1.73–4.05).  The AUC for the female derivation cohort was 0.97 (95% CI, 0.95–0.99) and 0.94 (95% CI, 0.92–0.96) for male derivation cohort.  AUC in the female validation cohort was 0.91 (95% CI, 0.83-0.98) and male was 0.90 (95% CI, 0.84–0.97). The risk scores showed good calibration (female; x²=8.88, p = 0.18 and male; x²=13.11, p = 0.07). 

Conclusion

A gender specific risk score for ADHF was developed and validated successfully in our Asian population. This will change our practice in providing valuable prognostic information in both female and male thereby guiding the need for more intensive treatment. Abstract Figure. ROC Curves (Female and Male)  Abstract Figure. Key Variables (Female and Male)

Mutant clones in normal epithelium outcompete and eliminate emerging tumours

Human epithelial tissues accumulate cancer-driver mutations with age1-9, yet tumour formation remains rare. The positive selection of these mutations suggests that they alter the behaviour and fitness of proliferating cells10-12. Thus, normal adult tissues become a patchwork of mutant clones competing for space and survival, with the fittest clones expanding by eliminating their less competitive neighbours11-14. However, little is known about how such dynamic competition in normal epithelia influences early tumorigenesis. Here we show that the majority of newly formed oesophageal tumours are eliminated through competition with mutant clones in the adjacent normal epithelium. We followed the fate of nascent, microscopic, pre-malignant tumours in a mouse model of oesophageal carcinogenesis and found that most were rapidly lost with no indication of tumour cell death, decreased proliferation or an anti-tumour immune response. However, deep sequencing of ten-day-old and one-year-old tumours showed evidence of selection on the surviving neoplasms. Induction of highly competitive clones in transgenic mice increased early tumour removal, whereas pharmacological inhibition of clonal competition reduced tumour loss. These results support a model in which survival of early neoplasms depends on their competitive fitness relative to that of mutant clones in the surrounding normal tissue. Mutant clones in normal epithelium have an unexpected anti-tumorigenic role in purging early tumours through cell competition, thereby preserving tissue integrity.

P252 Identifying predictors for all-cause mortality at admission, 1 and 3 years after admission for acute decompensated heart failure amongst patients with atrial fibrillation

Background

Heart failure (HF) and atrial fibrillation (AF) commonly co-exist, each, predisposing the other. AF may inflict haemodynamic disturbances, leading to reduced cardiac output and hence acute decompensation. Ultimately mortality risk is further increased. Identifying contributing factors is thus vital lest increasing risk of poor outcome.

Purpose

Identify predictors of all-cause mortality in AF patients after admission for acute decompensation HF (ADHF) at admission, 1 and 3 years. 

Methods

A retrospective observational study of 810 AF patients" first admission from 2009 to 2018, analysed using descriptive, ROC curve and Cox regression.

Results

Mortality at admission, 1 and 3 years following ADHF were 5.1%, 14.4% and 40.5% respectively. Majority of AF patients were male (64.7%) but there was no significant statistical difference between gender with associated mortality during those timelines. Using multivariate analysis, predictors associated with increased in-hospital mortality were Hyponatraemia, Na < 135mmol/L (adjusted Odds Ratio, aOR 2.49; 95% Confidence Interval, CI 1.91-5.20; p0.015), Uric Acid ≥ 675 (aOR 2.75; CI 1.31-5.79; p0.008), Ejection Fraction, EF < 40% (aOR 3.93; CI 1.63-9.49; p0.002). Medications on admission associated with reduced inpatient mortality were Angiotensin Converting Enzyme inhibitor (ACEi) / Angiotensin Receptor Blocker (ARB) + Beta Blocker (BB) + Mineralocorticoid Receptor Antagonist (MRA) (aOR 0.07; CI 0.02-0.30; p < 0.001). At 1 year, multivariate analysis showed an associated increase in mortality when NTProBNP ≥ 7500pg/ml (adjusted Hazard Ratio, aHR 1.64; CI 1.02-2.65; p0.042) and Urea > 7mmol/L (aHR 1.86; CI 1.04-3.32, p0.036). Medications on discharge comprising ACEi/ARB + BB + MRA were the only combination that showed a reduction in mortality (aHR 0.23; CI 0.09-0.60; p0.003). At 3 years, background coronary artery disease (aHR 1.72; CI 1.09-2.71; p0.02), hypernatraemia, Na > 145mmol/L (aHR 14.89; CI 3.17-69.86; p0.001), EF < 40% (aHR 2.00; CI 1.28-3.12; p0.002) were associated with increased mortality. Medications on discharge namely ACEi/ARB (aHR 0.14; CI 0.03-0.70; p0.013), BB (aHR 0.23; CI 0.10-0.51; p < 0.001), ACEi/ARB + BB (aHR 0.16; CI0.06-0.41; p < 0.001), ACEi/ARB + MRA (aHR 0.34; CI 0.14-0.85; p0.021), BB + MRA (aHR 0.38; CI 0.17-0.83; p0.016), ACEi/ARB + BB + MRA (aHR 0.193; CI 0.09-0.43; p < 0.001) showed an associated reduction in mortality.

Conclusions

In this single centre study, patients with AF who presented with ADHF had a variety of mortality predictors that influence at different timelines. They had higher risk of inpatient mortality with hyponatraemia, hyperuricaemia and EF < 40%. Elevated NTProBNP and Urea levels seemed to have more effect on mortality at 1 year compared to 3 years. Having 3 disease-modifying heart failure medications at discharge exerted the most benefit up to 3 years of follow up.

Abstract P252 Figure.

Comparison of amlodipine/valsartan/hydrochlorothiazide single pill combination and free combination: adherence, persistence, healthcare utilization and costs

OBJECTIVES

To determine whether amlodipine/valsartan/hydrochlorothiazide single pill combination (SPC) is associated with improved persistence, adherence and reduced healthcare utilization and costs compared to the corresponding free combination (FC).

METHODS

Adult (≥18 years) patients covered by commercial and Medicare Supplemental insurance in the Truven MarketScan database with hypertension (HTN) diagnosis between October 2009 and December 2011 were included. At least two filled prescriptions for the SPC cohort or two periods of minimum 15 days of concurrent use of amlodipine, valsartan and hydrochlorothiazide (HCT) for the FC cohort were required. Cohorts were propensity score matched (PSM) to balance on important confounders. Outcomes included: 1) adherence (proportion of days covered [PDC] and medication possession ratio [MPR]); 2) persistence (treatment gap >30 days); 3) all-cause and HTN-specific healthcare utilization and costs at 12 months.

RESULTS

After cohort matching with PSM, patients taking SPC (N = 9221) exhibited better outcomes than FC (N = 1884): higher mean adherence (85.7% vs. 77.0%), mean PDC (73.8% vs. 60.6%) and persistence (46.8% vs. 23.6%) (all p < 0.0001). Patients taking SPC were associated with higher odds of persistence (OR: 3.51; 95% CI: 3.08-4.02), MPR ≥80% (OR: 2.72; 95% CI: 2.40-3.08) and PDC ≥80% (OR: 2.88; 95% CI: 2.55-3.26). After PSM, the SPC cohort exhibited statistically significantly lower mean number of resource utilization events compared to FC. Patients in the SPC cohort also had a statistically significantly (p < 0.05) lower percentage of patients with ≥1 all-cause hospitalization (15.0% vs. 18.2%), ≥1 all-cause emergency room (ER) visits (25.7 vs. 31.4%), and ≥1 ER HTN-specific visits (9.7% vs. 14.1%). The costs incurred by SPC cohort patients were 2.8% to 41.7% numerically lower than the FC cohort, statistically significant for all-cause ER costs ($430.6 vs. $549.5, p < 0.05).

CONCLUSIONS

Real-world data indicate an association of the amlodipine/valsartan/HCT SPC with improved adherence and persistence vs. FC with no difference in overall healthcare or hypertension specific costs between the cohorts.

An incremental approach to pigmented skin lesion segmentation with classification refinements in uncertain regions

Skin lesion segmentation in dermatoscopic images is difficult because there are large inter variations in shape, size, color, and texture between lesions and skin types. Hence, computational features learned from a training set of lesion images may not be applicable to other lesion images. In this paper, we propose an incremental method for lesion segmentation. It leverages the Expectation-Maximization algorithm to find an initial segmentation. A new adaptive method is proposed to define two types of segmented regions: the high-confident and the low-confident. We train a support vector machine, using computational features from the high-confident regions, to further refine segmentation and, hence, achieve improved results for the low-confident regions. Validation experiments of our proposed method are performed on 319 dermatoscopy images and we have achieved good results with precision and recall to be 0.864 and 0.875 respectively.

Transradial percutaneous coronary intervention in acute ST elevation myocardial infarction and high-risk patients: experience in a single centre without cardiothoracic surgical backup

INTRODUCTION

Primary transradial percutaneous coronary intervention (TRI) is shown to be efficacious in stable patients with acute coronary syndrome. We aimed to evaluate the application of primary TRI for acute ST elevation myocardial infarction (STEMI), including among high-risk patients from our registry.

METHODS

This was a single-centre case series comprising 138 patients who underwent primary TRI for STEMI between May 2007 and June 2008. TRI was attempted with a 6-Fr guiding catheter in all patients regardless of Killip class status. Outcome measures were success rates of primary TRI, door-to-balloon time, procedure duration and volume of contrast used. All patients were followed up for major adverse cardiac events in-hospital, at 30 days and six months.

RESULTS

A total of 138 patients had primary TRI attempted for STEMI. Four patients failed primary TRI and required a femoral approach. The remaining 134 patients underwent primary TRI. The mean patient age was 56.4 years. Most patients with acute STEMI presented in Killip class I and II (91.8 percent). Only 8.2 percent were in Killip class III or IV on admission. 50 percent of patients presented with anterior STEMI. The median door-to-balloon time for this group was 92 (interquartile range [IQR] 77-121) minutes, with a median procedure time of 39 (IQR 29-51) minutes. The success rate of primary TRI was 97.1 percent.

CONCLUSION

Success rate, procedural and radiation time for TRI are comparable to those achieved via the femoral approach. Primary TRI is therefore a feasible and effective approach for acute STEMI, even in high-risk patients.

Effects on blood pressure and cardiovascular risk of variations in patients' adherence to prescribed antihypertensive drugs: role of duration of drug action

AIM

To determine the effects of imperfect adherence (i.e. occasionally missing prescribed doses), and the influence of rate of loss of antihypertensive effect during treatment interruption, on the predicted clinical effectiveness of antihypertensive drugs in reducing mean systolic blood pressure (SBP) and cardiovascular disease (CVD) risk.

METHOD

The effects of imperfect adherence to antihypertensive treatment regimens were estimated using published patterns of missed doses, and taking into account the rate of loss of antihypertensive effect when doses are missed (loss of BP reduction in mmHg/day; the off-rate), which varies between drugs. Outcome measures were the predicted mean SBP reduction and CVD risk, determined from the Framingham Risk Equation for CVD.

RESULTS

In patients taking 75% of prescribed doses (typical of clinical practice), only long-acting drugs with an off-rate of ∼1 mmHg/day were predicted to maintain almost the full mean SBP-lowering effect throughout the modelled period. In such patients, using shorter-acting drugs (e.g. an off-rate of ∼5-6 mmHg/day) was predicted to lead to a clinically relevant loss of mean SBP reduction of > 2 mmHg. This change also influenced the predicted CVD risk reduction; in patients with a baseline 10-year CVD risk of 27.0% and who were taking 75% of prescribed doses, a difference in off-rate from 1 to 5 mmHg/day led to a predicted 0.5% absolute increase in 10-year CVD risk.

CONCLUSIONS

In patients who occasionally miss doses of antihypertensives, modest differences in the rate of loss of antihypertensive effect following treatment interruption may have a clinically relevant impact on SBP reduction and CVD risk. While clinicians must make every effort to counsel and encourage each of their patients to adhere to their prescribed medication, it may also be prudent to prescribe drugs with a low off-rate to mitigate the potential consequences of missing doses.

Integrating spatial fuzzy clustering with level set methods for automated medical image segmentation

The performance of the level set segmentation is subject to appropriate initialization and optimal configuration of controlling parameters, which require substantial manual intervention. A new fuzzy level set algorithm is proposed in this paper to facilitate medical image segmentation. It is able to directly evolve from the initial segmentation by spatial fuzzy clustering. The controlling parameters of level set evolution are also estimated from the results of fuzzy clustering. Moreover the fuzzy level set algorithm is enhanced with locally regularized evolution. Such improvements facilitate level set manipulation and lead to more robust segmentation. Performance evaluation of the proposed algorithm was carried on medical images from different modalities. The results confirm its effectiveness for medical image segmentation.

ST segment elevation myocardial infarction following elective direct current synchronised cardioversion for atrial fibrillation

Atrial fibrillation is the most common arrhythmia in clinical practice. There is no difference in mortality, incidence of stroke or quality of life regardless of whether the rhythm control or rate control strategy is used. However, in certain circumstances, such as when rate control is inadequate, rhythm control is a viable option. We present a 74-year-old Eurasian man with a history of hypertension who presented with new-onset atrial fibrillation and sustained an ST segment elevation myocardial infarction following elective direct current cardioversion.

Accurate measurement of bone mineral density using clinical CT imaging with single energy beam spectral intensity correction

Although dual-energy X-ray absorptiometry (DXA) offers an effective measurement of bone mineral density, it only provides a 2-D projected measurement of the bone mineral density. Clinical computed tomography (CT) imaging will have to be employed for measurement of 3-D bone mineral density. The typical dual energy process requires precise measurement of the beam spectral intensity at the 80 kVp and 120 kVp settings. However, this is not used clinically because of the extra radiation dosage and sophisticated hardware setup. We propose an accurate and fast approach to measure bone material properties with single energy scans. Beam hardening artifacts are eliminated by incorporating the polychromatic characteristics of the X-ray beam into the reconstruction process. Bone mineral measurement from single energy CT correction is compared with that of dual energy correction and the commonly used DXA. Experimental results show that single energy correction is compatible with dual energy CT correction in eliminating beam hardening artifacts and producing an accurate measurement of bone mineral density. We can then estimate Young's modulus, yield stress, yield strain and ultimate tensile stress of the bone, which are important data for patient specific therapy planning.

Medical image segmentation using watershed segmentation with texture-based region merging

The use of the watershed algorithm for image segmentation is widespread because it is able to produce a complete division of the image. However, it is susceptible to over-segmentation and in medical image segmentation, this meant that that we do not have good representations of the anatomy. We address this issue by thresholding the gradient magnitude image and performing post-segmentation merging on the initial segmentation map. The automated thresholding technique is based on the histogram of the gradient magnitude map while the post-segmentation merging is based on the similarity in textural features (namely angular second moment, contrast, entropy and inverse difference moment) belonging to two neighboring partitions. When applied to the segmentation of various facial anatomical structures from magnetic resonance (MR) images, the proposed method achieved an overlap index of 92.6% compared to manual contour tracings. It is able to merge more than 80% of the initial partitions, which indicates that a large amount of over-segmentation has been reduced. Results produced using watershed algorithm with and without the proposed and proposed post-segmentation merging are presented for comparisons.

Issues in blood pressure control and the potential role of single-pill combination therapies

Hypertension (HTN) is a major risk factor for cardiovascular mortality, yet only a small proportion of hypertensive individuals receive appropriate therapy and achieve target blood pressure (BP) values. Factors influencing the success of antihypertensive therapy include physicians' acceptance of guideline BP targets, the efficacy and tolerability of the drug regimen, and patient compliance and persistence with therapy. It is now well recognised that most hypertensive patients require at least two antihypertensive agents to achieve their target BP. However, complicated treatment regimens are a major contributory factor to poor patient compliance. The use of combination therapy for HTN offers a number of advantages over the use of monotherapy, including improved efficacy, as drug combinations with a synergistic mechanism of action can be used. This additive effect means that lower doses of the individual components can be used, which may translate into a decreased likelihood of adverse events. The use of single-pill combination therapy, in which two or more agents are combined in a single dosage form, offers all the benefits of free combination therapy (improved efficacy and tolerability over monotherapy) together with the added benefit of improved patient compliance because of the simplified treatment regimen. The use of single-pill combination therapy may also be associated with cost savings compared with the use of free combinations for reasons of cheaper drug costs, fewer physician visits and fewer hospitalisations for uncontrolled HTN and cardiovascular events. Thus, the use of single-pill combination therapy for HTN should help improve BP goal attainment through improved patient compliance, leading to reduced costs for cardiovascular-related care.

Stonefish envenomation presenting to a Singapore hospital

INTRODUCTION

Stonefish, belonging to the genus Synanceia and classified under the Synanceiidae family, are commonly found in the shallow waters of the Indo-Pacific region and are considered the most dangerous and venomous of this family. The aim of the study was to describe the presenting features, clinical course and current management of this series of patients with stonefish envenomation presenting to a tertiary general hospital in Singapore.

METHODS

Data involving stonefish stings was retrospectively retrieved from the Singapore General Hospital Accident & Emergency Emerge Version 3.7.6 database from October 2004 to September 2006. Information, such as the patients' demographics, date and location of the incident, identity of the fish, local or systemic effects, pain score (upon arrival and after treatment), investigations and treatment as well as the outcome of the patients, were evaluated.

RESULTS

30 cases were identified. The median age of the patients was 28 years. The majority of patients were male (80 percent) and 47 percent of cases were foreign nationals. Most incidences occurred on weekends/public holidays (77 percent), with November having the highest number of cases (seven cases). The majority of cases (80 percent) arrived at the hospital within two hours of envenomation. Symptoms included extreme pain, swelling and redness of the affected limbs. 24 (80 percent) patients received hot water soak treatment and 27 (90 percent) patients received either intramuscular pethidine or diclofenac for analgesia, where nine patients (33 percent) required additional analgesics after a period of observation. 17 patients (58 percent) were treated and discharged, eight (26 percent) were referred to a specialist for follow-up and five (16 percent) were admitted for an average of three days. 13 out of 25 patients (52 percent) were discharged with antibiotics. One case complained of persistent pain and hyperalgesia five months post-envenomation. One patient required surgical intervention. No deaths and systemic symptoms were reported.

CONCLUSION

Cases of stonefish envenomation that presented to our hospital showed that the majority of patients were young male adults. Stonefish envenomation, though it rarely kills, can cause extreme pain, swelling and erythema, which can be managed with symptomatic treatment.

Automatic working area classification in peripheral blood smears without cell central zone extraction

In this paper we study automatic classification of working areas in peripheral blood smears using image analysis and recognition methods. Such automatic classification can provide objective and reproducible quality control for the evaluation of smears and smear maker devices. However, research in this filed has drawn little attention. Existing methods either can not differentiate correctly different cell distributions or rely on the extraction of the central pallor zones in cells for counting, which are not always observable. In contrast, we do not rely on the pallor zone extraction thus on more general basis. We introduce two generic parameters to measure the goodness of working areas, one for the degree of overlap, and the other for the spatial occupancy. We also propose a cascading classification network for the classification of different areas. The effectiveness of our method has been tested on over 150 labeled images acquired from three malaria-infected Giemsa-stained blood smears using an oil immersion 100 x objective.

Generalized negative binomial distribution: a promising statistical distribution for Oncomelania hupensis in the lake- and marsh-land regions of China

A new generalization of the negative binomial distribution (GNBD) is introduced and fitted to counts of Oncomelania hupensis, the intermediate host of Schistosoma japonicum, made, in areas of Chinese lakeland and marshland, early in the winter of 2005 and late in the spring of 2006. The GNBD was found to fit the snail data better than the standard negative binomial distribution (NBD) that has previously been widely used to model the distribution of O. hupensis. With two more parameters than the NBD, the GNBD can integrate many discrete distributions and is more flexible than the NBD in modelling O. hupensis. It also provides a better theoretical distribution for the quantitative study of O. hupensis, especially in building an accurate prediction model of snail density. The justification for adopting the GNBD is discussed. The GNBD allows researchers to broaden the field in the quantitative study not only of O. hupensis and schistosomiasis japonica but also of other environment-related helminthiases and family-clustered diseases that have, traditionally, been modelled using the NBD.

Spectrogram denoising and automated extraction of the fundamental frequency variation of dolphin whistles

Marine mammal vocalizations are often analyzed using time-frequency representations (TFRs) which highlight their nonstationarities. One commonly used TFR is the spectrogram. The characteristic spectrogram time-frequency (TF) contours of marine mammal vocalizations play a significant role in whistle classification and individual or group identification. A major hurdle in the robust automated extraction of TF contours from spectrograms is underwater noise. An image-based algorithm has been developed for denoising and extraction of TF contours from noisy underwater recordings. An objective procedure for measuring the accuracy of extracted spectrogram contours is also proposed. This method is shown to perform well when dealing with the challenging problem of denoising broadband transients commonly encountered in warm shallow waters inhabited by snapping shrimp. Furthermore, it would also be useful with other types of broadband transient noise.

Medical image segmentation using feature-based GVF snake

We propose a feature-based GVF snake for medical image segmentation here. Feature-based criteria are introduced for the GVF snake to stop its iterations. Without these criteria, the GVF snake might continue its iterations even though it has converged at the targeted object and result in longer computational time. The feature here is the area of the targeted object. Our proposed method comprises of two stages, namely the training stage and the segmentation stage. In the training stage, we acquire prior knowledge on the relative area of the targeted object from training data. In the segmentation stage, the proposed feature-based GVF snake is applied to segment the object from the image after computing the estimated area of the targeted object. In our proposed method, the GVF snake stops its iterations when the area bounded by its propagation is approximately equal to the estimated area and when it undergoes little change over two consecutive iterations. To illustrate the effectiveness of our proposed method, we applied it to the segmentation of the masseter muscle, which is the strongest jaw muscle, from 2-D magnetic resonance (MR) images. Numerical evaluation done indicates good agreement between the computerized and manual segmentations, with mean overlap of 92%.

Masseter segmentation using an improved watershed algorithm with unsupervised classification

The watershed algorithm always produces a complete division of the image. However, it is susceptible to over-segmentation and sensitivity to false edges. In medical images this leads to unfavorable representations of the anatomy. We address these drawbacks by introducing automated thresholding and post-segmentation merging. The automated thresholding step is based on the histogram of the gradient magnitude map while post-segmentation merging is based on a criterion which measures the similarity in intensity values between two neighboring partitions. Our improved watershed algorithm is able to merge more than 90% of the initial partitions, which indicates that a large amount of over-segmentation has been reduced. To further improve the segmentation results, we make use of K-means clustering to provide an initial coarse segmentation of the highly textured image before the improved watershed algorithm is applied to it. When applied to the segmentation of the masseter from 60 magnetic resonance images of 10 subjects, the proposed algorithm achieved an overlap index (kappa) of 90.6%, and was able to merge 98% of the initial partitions on average. The segmentation results are comparable to those obtained using the gradient vector flow snake.

New insights into image processing of cortical blood flow monitors using laser speckle imaging

Laser speckle imaging has increasingly become a viable technique for real-time medical imaging. However, the computational intricacies and the viewing experience involved limit its usefulness for real-time monitors such as those intended for neurosurgical applications. In this paper, we propose a new technique, tLASCA, which processes statistics primarily in the temporal direction using the laser speckle contrast analysis (LASCA) equation, proposed by Briers and Webster. This technique is thoroughly compared with the existing techniques for signal processing of laser speckle images, including, the spatial-based sLASCA and the temporal-based modified laser speckle imaging (mLSI) techniques. sLASCA is an improvement of the basic LASCA technique. In sLASCA, the derived contrasts are further averaged over a predetermined number of raw speckle images. mLSI, on the other hand, is the technique in which temporal statistics are processed using the equation described by Ohtsubo and Asakura. tLASCA preserves the original image resolution similar to mLSI. tLASCA outperforms sLASCA (window size M = 5) with faster convergence of K values (5.32 versus 20.56 s), shorter per-frame processing time (0.34 versus 2.51 s), and better subjective and objective quality evaluations of contrast images. tLASCA also outperforms mLSI with faster convergence of K values (5.32 s) compared to N values (10.44 s), shorter per-frame processing time (0.34 versus 0.91 s), smaller intensity fluctuations among frames (8%-10% versus 15%-35%), and better subjective and objective quality evaluations of contrast images. As laser speckle imaging becomes an important tool for real-time monitoring of blood flows and vascular perfusion, tLASCA is proven to be the technique of choice.

3D statistical models for tooth surface reconstruction

This paper presents a method to reconstruct the 3D surface of a tooth given partial information about its shape. A statistical model comprising a mean shape and a series of deformation modes is obtained offline using a set of specimens. During reconstruction, rigid registration is performed to align the mean shape with the target. The mean shape is then deformed to approximate the target by minimizing the sum of squared distances between the two surfaces according to the deformation modes. The method is shown to be efficient for the recovery of tooth shape given crown information.