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PubMedDate not supplied

Serological assessment of type I collagen burden in scleroderma spectrum disorders: a systematic review.

RATIONALE: The aim of the study was to evaluate the validity of collagen type I metabolites as markers of disease activity in scleroderma (SSc), through a systematic review of the literature and by validating the results by measuring collagen type I metabolites in well characterized patients with scleroderma spectrum disorders and in Raynaud's phenomenon. METHODS: A systematic review was performed of studies of collagen type I metabolites in scleroderma spectrum disorders published from 1980 to 2003. The collected results from the literature were compared with our own measurements of collagen type I metabolites (PINP and ICTP) in a small number of well characterized patients within the scleroderma spectrum and in patients with primary and "autoimmune" Raynaud's phenomenon. Peptide concentrations from all sources, including the present study, were compared. Reported correlations between peptide concentrations and clinical variables were also analysed. RESULTS: Of 19 papers identified by an extensive Medline search, 12 were eligible for systematic analysis. There was a considerable heterogeneity in the results with a wide range of metabolite concentrations. Values from disease groups and healthy controls overlapped. These findings were confirmed by our study where, similarly, there was a large range of values in all groups, but particularly in the diffuse SSc subset. When the correlation between peptide levels and clinical variables was assessed, large discordance between the studies was observed. CONCLUSIONS: We have not found sufficient evidence to support the use of serum markers of collagen turnover in the assessment of scleroderma activity and severity, in view of their low specificity and the heterogeneity of the results of various studies. Lack of standardized routine evaluation of SSc patients in clinical studies might have accounted for the variability of the findings. However, due to the small sizes of most published studies, demonstration of no effect should come from large-scale randomised trials. Longitudinal serial analysis of these molecules in individual patients may play a future role in the evaluation of the response to fibroblast-targeting therapeutic strategies in scleroderma patients.

Biomarkers↗

PubMed2004

Implementing evidence-based practice in undergraduate teaching clinics: a systematic review and recommendations.

The objective of this project was to identify an effective methodology of approaching and implementing evidence-based principles in undergraduate teaching clinics to promote evidence-based dentistry in future clinical practice. A systematic review was undertaken to examine evidence-based clinical teaching and faculty continuing education. Research published from 1996 to 2002 was retrieved by searching several databases and the Internet, along with conducting hand searches and reviewing bibliographies maintained by faculty experts. Qualitative checklists for different types of studies were created to evaluate the literature. Relevant studies were selected if they met all four predetermined essential criteria and a minimum of two out of three desirable criteria. Systematic reviews were chosen if they met all five essential criteria. Data from selected articles were extracted, and study quality was assessed. We found that three systematic reviews and nine original research articles were deemed methodologically acceptable. Problem-based learning and evidence-based health care interventions increased student knowledge of medical topics and their ability to search, evaluate, and appraise medical literature. Dental students in a problem-based learning curriculum, emphasizing evidence-based practices, scored higher on the NDB I (National Dentistry Boards, Part I) than students in traditional curricula. While effective modules in implementing theoretical evidence-based principles exist, very few high-quality studies are available that examine these principles in dental undergraduate teaching clinics. No methodologically appropriate studies on the education of faculty in the implementation of evidence-based principles are available. Some studies promote promising theories and methodologies of teaching evidence-based care; based on these theories, a comprehensive model is proposed in this article. Considering the strength of evidence in the reviewed literature, we concluded that an evidence-based approach to clinical care is effective.

Curriculum↗

PubMed2005

A systematic review of nutritional rickets in Ethiopia: status and prospects.

BACKGROUND: Nutritional rickets contributes to the high burden of illness and death among Ethiopian children below 5 years of age. Lack of adequate information appears to have negatively influenced the impact of prevention and treatment programs. OBJECTIVES: The objective of this systematic review is to review existing body of knowledge about nutritional rickets in Ethiopia and develop recommendations that will guide development of strategies for effective interventions and research. METHODS: Published and unpublished information on nutritional rickets in Ethiopia was collected systematically. The information was critically reviewed and discussed in the context of regional and global situation. RESULTS: The major cause of nutritional rickets in Ethiopian children is lack of exposure to sunshine and/or inadequate intake of vitamin D. Lack of awareness and traditional beliefs are major causes for not exposing infants to sunshine. The disease is associated with poor socioeconomic status, low birth weight, protein-energy malnutrition and common childhood infections. Severe form of rickets is commonly seen at about 18 months of age. Rickets predisposes Ethiopian children to pneumonia. Diagnostic criteria used in most studies include two or more clinical signs and a characteristic radiological or biochemical abnormality. There are critical gaps in our knowledge about the epidemiology, ecology, and potentially effective interventions to prevent and treat rickets in Ethiopian children. CONCLUSION: Most of the studies on nutritional rickets in Ethiopia have been conducted in hospital settings. There is a need for well designed epidemiological and ecological studies. The biologic basis for the striking association between PEM and active rickets seen in Ethiopia needs to be determined The role of calcium deficiency, the part played by genetic factors, the nature of the association between the duration of breastfeeding and rickets, and the role of complimentary feeds in Ethiopian children need to be explored. Studies are required to determine the amount of sunshine required to prevent rickets in Ethiopian infants. Studies are required to establish criteria for the diagnosis of clinical and sub clinical rickets, particularly in malnourished children. Prevention programs need to be pursued consistently and systematically and treatment options, including the single massive dose of vitamin D, need to be re-evaluated and optimal mode of treatment determined.

Child Nutrition Disorders↗

PubMed2006

Systematic reviews in midwifery.

This paper highlights the key steps to follow when conducting a systematic review (see Box 2). Healthcare practitioners may be limited by time and resources when conducting literature reviews, however, a systematic and transparent approach should be adopted wherever possible. Further detailed guidance on conducting systematic reviews is available from the NHS Centre for Reviews and Dissemination (NHS CRD, 2001) and the Cochrane Reviewers' Handbook (Alderson et al, 2003).

Databases, Bibliographic↗

PubMed1997

Alcohol misuse prevention for young people: a systematic review reveals methodological concerns and lack of reliable evidence of effectiveness.

In a systematic review we assessed the methodological quality of evaluations of alcohol misuse prevention programmes for young people, and recorded evidence of effectiveness. Studies were identified through systematic searches of electronic databases; hand searches of all obtained papers, existing reviews and several journals; and mailshots to key organizations, conferences and individuals. Relevant papers were checked and cross-checked by members of the review team, and only those studies with an experimental or quasi-experimental design and positive attributes on a number of other quality criteria were included in the review. After pre-screening over 500 papers which reported prevention programmes, information was systematically abstracted from 155 papers. Only 33 studies merited inclusion in the review, and most of these had some methodological shortcomings. Twenty-one studies reported some significant short- and medium-term reductions in drinking behaviour. Of two studies which carried out longer-term evaluations, only one reported a significant longer-term effect, with small effect sizes. No factors clearly distinguished partially effective from ineffective or harmful prevention programmes. In conclusion, the lack of reliable evidence means that no one type of prevention programme can be recommended. In particular there is a need to carry out well-designed scientific evaluations of the effectiveness of current or new prevention efforts which target young people's alcohol misuse.

Adolescent↗

PubMed2026

The application of artificial intelligence in healthcare practice: A mapping review of systematic reviews.

Artificial intelligence (AI) is rapidly transforming healthcare practice, with growing evidence supporting its use in diagnosis, prognosis, treatment planning, and operational decision-making. The proliferation of systematic reviews in recent years underscores the need for an updated synthesis of the literature to inform research, policy, and practice. We searched PubMed, Web of Science, Scopus, IEEE Xplore, and CINAHL for systematic reviews and meta-analyses published between 2019 and February 2026. Eligible reviews focused on AI applications in healthcare practice, were peer-reviewed, and written in English. A total of 368 reviews met the inclusion criteria. Publication volume increased steadily, peaking in 2025. AI research was concentrated in high-density domains, such as radiology, oncology, and critical care. Across reviews, diagnostic imaging, electronic health record (EHR) data, and biomarkers/laboratory results accounted for 68% of training data sources, though newer data types, such as wearable device and sensor data, emerged from 2022 onward. Diagnosis, prognosis, and treatment comprised over 80% of AI applications, with novel uses emerging in recent years, such as AI-assisted clinical documentation (e.g., ambient documentation tools) and patient education. Ethical concerns were reported in 78.5% of reviews, with privacy, model accuracy, data and algorithmic bias, and explainability as recurrent themes. The proportion of reviews reporting ethical concerns increased from 2021 to 2025. AI applications in healthcare are expanding in scope, diversifying in data sources, and evolving toward novel clinical and operational uses. The human-centered AI or augmented intelligence paradigm, integrating computational precision with clinical expertise, holds significant promise but will require parallel advances in governance, regulatory frameworks, and ethical oversight to ensure safe adoption.

Artificial Intelligence↗

PubMedDate not supplied

Effects of a systematic approach to tobacco cessation in a community-based practice.

Studies suggest that the absence of a systematic approach is a barrier to the provision of tobacco cessation counseling services in clinical practice. A systematic intervention was shown to be feasible and effective at a faculty practice site. Our pilot study examined the feasibility of implementation at a community-based practice and assessed the effect of the tobacco cessation counseling system on our patients' smoking behavior. Systematic assessment (smoking status, "readiness to quit"), brief counseling at each visit, and follow-up (for those ready to quit) were provided by a physician and nurse team. Our results suggest that the office-based tobacco cessation counseling system can work in a community-based practice and is an effective strategy for helping smokers quit and in preparing to quit.

Adult↗

PubMed2000

Systematic implementation of an advance directive program in nursing homes: a randomized controlled trial.

CONTEXT: Although advance directives are commonly used in the community, little is known about the effects of their systematic implementation. OBJECTIVES: To examine the effect of systematically implementing an advance directive in nursing homes on patient and family satisfaction with involvement in decision making and on health care costs. DESIGN: Randomized controlled trial conducted June 1, 1994, to August 31, 1998. SETTING AND PARTICIPANTS: A total of 1292 residents in 6 Ontario nursing homes with more than 100 residents each. INTERVENTION: The Let Me Decide advance directive program included educating staff in local hospitals and nursing homes, residents, and families about advance directives and offering competent residents or next-of-kin of mentally incompetent residents an advance directive that provided a range of health care choices for life-threatening illness, cardiac arrest, and nutrition. The 6 nursing homes were pair-matched on key characteristics, and 1 home per pair was randomized to take part in the program. Control nursing homes continued with prior policies concerning advance directives. MAIN OUTCOME MEASURES: Residents' and families' satisfaction with health care and health care services utilization over 18 months, compared between intervention and control nursing homes. RESULTS: Of 527 participating residents in intervention nursing homes, 49% of competent residents and 78% of families of incompetent residents completed advance directives. Satisfaction was not significantly different in intervention and control nursing homes. The mean difference (scale, 1-7) between intervention and control homes was -0.16 (95 % confidence interval [CI], -0.41 to 0.10) for competent residents and 0.07 (95% CI, -0.08 to 0.23) for families of incompetent residents. Intervention nursing homes reported fewer hospitalizations per resident (mean, 0.27 vs 0.48; P = .001) and less resource use (average total cost per patient, Can $3490 vs Can $5239; P = .01) than control nursing homes. Proportion of deaths in intervention (24%) and control (28%) nursing homes were similar (P = .20). CONCLUSION: Our data suggest that systematic implementation of a program to increase use of advance directives reduces health care services utilization without affecting satisfaction or mortality.

Advance Directives↗

PubMed2004

Efficacy and bleeding complications among patients randomized to enoxaparin or unfractionated heparin for antithrombin therapy in non-ST-Segment elevation acute coronary syndromes: a systematic overview.

CONTEXT: Antithrombin therapy has become a guidelines-recommended standard of care in the treatment of acute coronary syndromes (ACS), but recent trials comparing use of enoxaparin and unfractionated heparin in ACS have yielded less robust efficacy and safety results than have earlier trials of these antithrombin therapies. OBJECTIVE: To systematically evaluate the end points of all-cause death and nonfatal myocardial infarction (MI), transfusion, and major bleeding observed in the 6 randomized controlled trials comparing enoxaparin and unfractionated heparin in treatment of ACS. DATA SOURCES: The primary data sets for ESSENCE, A to Z, and SYNERGY were available at the Duke Clinical Research Institute. Baseline characteristics and event frequencies for TIMI 11B, ACUTE II, and INTERACT were provided by the principal investigator of each study. STUDY SELECTION: All 6 randomized controlled trials comparing enoxaparin and unfractionated heparin in non-ST-segment elevation ACS were selected for analysis. DATA EXTRACTION: Efficacy and safety end points were extracted from the overall trial populations and the subpopulation receiving no antithrombin therapy prior to randomization. DATA SYNTHESIS: Systematic evaluation of the outcomes for 21 946 patients was performed using a random-effects empirical Bayes model. No significant difference was found in death at 30 days for enoxaparin vs unfractionated heparin (3.0% vs 3.0%; odds ratio [OR], 1.00; 95% confidence interval [CI], 0.85-1.17). A statistically significant reduction in the combined end point of death or nonfatal MI at 30 days was observed for enoxaparin vs unfractionated heparin in the overall trial populations (10.1% vs 11.0%; OR, 0.91; 95% CI, 0.83-0.99; number needed to treat, 107). A statistically significant reduction in the combined end point of death or MI at 30 days was also observed for enoxaparin in the populations receiving no prerandomization antithrombin therapy (8.0% vs 9.4%; OR, 0.81; 95% CI, 0.70-0.94; number needed to treat, 72). No significant difference was found in blood transfusion (OR, 1.01; 95% CI, 0.89-1.14) or major bleeding (OR, 1.04; 95% CI, 0.83-1.30) at 7 days after randomization in the overall safety population or in the population of patients receiving no prerandomization antithrombin therapy. CONCLUSION: In a systematic overview of approximately 22 000 patients across the spectrum of ACS, enoxaparin is more effective than unfractionated heparin in preventing the combined end point of death or MI.

Angina Pectoris↗

PubMed1999

A systematic nomenclature for new translation initiation factor genes from S. pombe and other fungi.

Eukaryotic translation initiation factors and their corresponding genes have been characterized using biochemical and genetic methods from a variety of different organisms. The designations of the factors relate to their apparent roles in the biochemical process. Many gene names indicate genetic interactions with other genes or the functional attributes used to identify them. On the other hand, progress in systematic sequencing of the genomes of organisms like Saccharomyces cerevisiae and Schizosaccharomyces pombe has revealed many genes homologous to known translation initiation factor genes. The genes defined by the systematic sequencing approach are assigned numerical designations completely unrelated to their biological function. So far there have been publications on only three genes encoding translation initiation factors from Schizosaccharomyces pombe. We therefore see this an an ideal opportunity to propose a systematic and logical nomenclature for genes encoding translation initiation factor genes that can be applied to all further genes of this type that are characterized in this fission yeast.

Fungi↗

PubMed1997

Radiotherapy for localized prostate carcinoma. The correlation of pretreatment prostate specific antigen and nadir prostate specific antigen with outcome as assessed by systematic biopsy and serum prostate specific antigen.

BACKGROUND: The objective of this study was to correlate the failure pattern of localized prostate carcinoma after radiotherapy (RT) with pretreatment (preTx) PSA and post-RT nadir PSA, using systematic biopsies and serum PSA in the assessment of outcome. METHODS: From January 1990 to February 1994, 207 patients treated with external beam RT were followed prospectively with systematic transrectal ultrasound-guided biopsies and measurements of serum PSA levels. Three hundred forty-three biopsies were performed, with 4-7 samples taken per session. The distribution of T classification was as follows: 19 patients had T1b, 15 had T1c, 34 had T2a, 79 had T2b/c, 53 had T3, and 7 had T4. Median follow-up was 36 months (range, 12-70 months). Failures were categorized as biochemical (chemF) (PSA > 2.0 ng/mL and > 1 ng/ mL over nadir), local (LF) (positive biopsy and PSA > 2), and distant (DF). The Cox proportional hazards model was used for multivariate analysis (MVA). RESULTS: Overall, failures were seen in 68 of 207 patients: 20 LF, 24 DF, 7 LF + DF, and 17 chemF. In univariate analysis, failures correlated significantly with preTx PSA, post-RT nadir PSA, T classification, and Gleason's score (GS). The total failure rate was 12% for T1b, T1c, and T2a; 39% for T2b and T2c; and 60% for T3 and T4 (P < 0.0001). By evaluation with preTx PSA, at 36 months the total failure rate was 3% for preTx PSA < or = 5 ng/mL 16% for 5.1-10 ng/mL, 32% for 10.1-15 ng/mL, 42% for 15.1-20 ng/mL, 63% for 20.1-50 ng/mL, and 88% for > 50 ng/mL (P < 0.0001). By evaluation with post-RT nadir PSA, at 36 months the total failure rate was 4% for nadir PSA < or = 0.5 ng/ mL, 26% for 0.6-1 ng/mL, 33% for 1.1-2 ng/mL, and 92% for > 2 ng/mL (P < 0.0001). In MVA, nadir PSA (P < 0.0001) and T classification (P < 0.0005) were independent predictors for any failure. LF occurred in 13% of patients (27 of 207). For these 27 patients, the categorization of T classification was: T1b/T1c/T2a, 7%; T2b/T2c, 16%; and T3/T4, 15% (P = not significant). In MVA, only nadir PSA (P = 0.0004) predicted for LF. DF occurred in 15% of patients (31 of 207). In MVA, nadir PSA (P < 0.0001) and T classification (P < 0.0001) predicted for DF, with pretreatment PSA of borderline significance (P < 0.05). To assess preTx predictors of outcome, post-RT nadir PSA was removed from the model. PreTx PSA then became the dominant variable to predict any failure (P < 0.0001), LF (P = 0.05), chemF (P = 0.0001), and DF (P < 0.003), while T classification also predicted for any failure (P = 0.03), chemF (P = 0.05), and DF (P < 0.0001). CONCLUSIONS: Systematic prostate biopsies, performed as part of the rigorous followup of prostate carcinoma after RT, define the patterns of failure and confirm the prognostic value of preTx PSA, post-RT nadir PSA, and T classification. Prior to treatment, preTx PSA is the overwhelming independent predictor of failure, but it is surpassed by post-RT nadir PSA when this is added to the model.

Aged↗

PubMed2000

SINE insertions: powerful tools for molecular systematics.

Short interspersed repetitive elements, or SINEs, are tRNA-derived retroposons that are dispersed throughout eukaryotic genomes and can be present in well over 10(4) total copies. The enormous volume of SINE amplifications per organism makes them important evolutionary agents for shaping the diversity of genomes, and the irreversible, independent nature of their insertion allows them to be used for diagnosing common ancestry among host taxa with extreme confidence. As such, they represent a powerful new tool for systematic biology that can be strategically integrated with other conventional phylogenetic characters, most notably morphology and DNA sequences. This review covers the basic aspects of SINE evolution that are especially relevant to their use as systematic characters and describes the practical methods of characterizing SINEs for cladogram construction. It also discusses the limits of their systematic utility, clarifies some recently published misunderstandings, and illustrates the effective application of SINEs for vertebrate phylogenetics with results from selected case studies. BioEssays 22:148-160, 2000.

Animals↗

PubMed2000

Nonlinear smoothing for reduction of systematic and random errors in diffusion tensor imaging.

Calculation and sorting of the eigenvectors of diffusion using diffusion tensor imaging has previously been shown to be sensitive to noise levels in the acquired data. This sensitivity manifests as random and systematic errors in the diffusion eigenvalues and derived parameters such as indices of anisotropy. An optimized application of nonlinear smoothing techniques to diffusion data prior to calculation of the diffusion tensor is shown to reduce both random and systematic errors, while causing little blurring of anatomical structures. Conversely, filtering applied to calculated images of fractional anisotropy is shown to fail in reducing systematic errors and in recovering anatomical detail. Using both real and simulated brain data sets, it is demonstrated that this approach has the potential to allow acquisition of data that would otherwise be too noisy to be of use.

Anisotropy↗

PubMed1994

Radical systematic mediastinal lymphadenectomy in non-small cell lung cancer: a randomized controlled trial.

The value of radical systematic lymphadenectomy in the treatment of bronchial carcinoma is controversial. In a randomized controlled clinical trial, radical lymphadenectomy was compared with conventional node dissection in 182 patients with non-small cell lung cancer. Comparison of short-term results revealed a significantly longer operating time in those undergoing systematic lymphadenectomy, but overall morbidity and mortality rates were comparable between groups. However, there were complications associated with radical lymphadenectomy such as prolonged air leakage and haemorrhage. Interim analysis of results at a median follow-up of 26.8 months showed no significant influence of radical lymphadenectomy on local recurrence-free interval, metastasis-free interval or cancer-related survival. In conclusion, radical systematic lymphadenectomy is a safe operation that leads to a better staging of non-small cell lung cancer, but its prognostic benefit is questionable.

Adult↗

PubMed1997

Prediction equations do not eliminate systematic error in self-reported body mass index.

Epidemiological studies of the risks of obesity often use body mass index (BMI) calculated from self-reported height and weight. The purpose of this study was to examine the pattern of reporting error associated with self-reported values of BMI and to evaluate the extent to which linear regression models predict measured BMI from self-reported data and whether these models could compensate for this reporting error. We examined measured and self-reported weight and height on 5079 adults aged 30 years to 64 years from the second National Health and Nutrition Examination Survey. Measured and self-reported BMI (kg/m2) was calculated, and multiple linear regression techniques were used to predict measured BMI from self-reported BMI. The error in self-reported BMI (self-reported BMI minus measured BMI) was not constant but varied systematically with BMI. The correlation between measured BMI and the error in self-reported BMI was -0.37 for men and -0.38 for women. The pattern of reporting error was only weakly associated with self-reported BMI, with the correlation being 0.05 for men and -0.001 for women. Error in predicted BMI (predicted BMI minus measured BMI) also varied systematically with measured BMI, but less consistently with self-reported BMI. More complex models only slightly improved the ability to predict measured BMI compared with self-reported BMI alone. None of the equations were able to eliminate the systematic reporting error in determining measured BMI values from self-reported data. The characteristic pattern of error associated with self-reported BMI is difficult or impossible to correct by the use of linear regression models.

Adult↗

PubMed1997

Systematic and random errors in compression testing of trabecular bone.

We sought to quantify the systematic and random errors associated with end-artifacts in the platens compression test for trabecular bone. Our hypothesis was that while errors may depend on anatomic site, they do not depend on apparent density and therefore have substantial random components. Trabecular bone specimens were first tested nondestructively using newly developed accurate protocols and then were tested again using the platens compression test. Percentage differences in modulus between the techniques (bovine proximal tibia [n = 18] and humerus [n = 17] and human lumbar spine, [n = 9]) were in the range of 4-86%. These differences did not depend on anatomic site (p = 0.21) and were only weakly dependent on apparent density and specimen aspect ratio (r2 < 0.10). The mean percentage difference in modulus was 32.6%, representing the systematic component of the end-artifact error. Neglecting the minor variations explained by density and specimen size (approximately 10%), an upper bound on the random error from end-artifacts in this experiment was taken as the SD of the modulus difference (+/-18.2%). Based on a synthesis of data taken from this study and from the literature, we concluded that the systematic underestimation error in the platens compression test can be only approximated and is in the range of 20-40%; the substantial random error (+/-12.5%) confounds correction, particularly when the sample size is small. These errors should be considered when interpreting results from the platens test, and more accurate testing techniques should be used when such errors are not acceptable.

Animals↗

PubMed1993

Analysis of systematic and random error in MR volumetric flow measurements.

The spatial aspects of error in 2D MR cine phase-velocity mapping are considered in order to define acquisition strategies which will minimize error in measuring volumetric flow. Error was separated into two categories: systematic and random. Potential sources of systematic error examined were intravoxel phase dispersion (IVPD), partial volume effects, misalignment of flow axis and flow-encoding gradients, and improper choice of vessel voxels for flux calculations. Random error was addressed using analysis of propagation of variance. Analytical expressions for sources of error were derived; and computer models were used to test the analytical models. Flow phantom studies examining error in MR volumetric flow measurements were performed and compared with error predicted by the analytical models. Expected error in several clinical situations of interest was then derived to find appropriate acquisition strategies. Spatial resolution, signal to noise ratio, velocity sensitivity and the ratio of the modulus of moving isochromats to that of static isochromats were found to be the most important parameters in controlling error and were found to cause competing effects with respect to systematic and random error.

Artifacts↗

PubMed2006

DSC perfusion MRI-Quantification and reduction of systematic errors arising in areas of reduced cerebral blood flow.

Dynamic susceptibility contrast (DSC)-MRI is commonly used to measure cerebral perfusion in acute ischemic stroke. Quantification of perfusion parameters involves deconvolution of the tissue concentration-time curves with an arterial input function (AIF), typically with the use of singular value decomposition (SVD). To mitigate the effects of noise on the estimated cerebral blood flow (CBF), a regularization parameter or threshold is used. Often a single global threshold is applied to every voxel, and its value has a dramatic effect on the CBF values obtained. When a single global threshold was applied to simulated concentration-time curves produced using exponential, triangular, and boxcar residue functions, significant systematic errors were found in the measured perfusion parameters. We estimate the errors obtained for different sampling intervals and signal-to-noise ratios (SNRs), and discuss the source of the systematic error. We present a method that partially corrects for the systematic error in the presence of an exponential residue function by applying a linear fit, which removes underestimates of long mean transit time (MTT) and overestimates of short MTT. For example, the correction reduced the error at a temporal resolution of 2.5 s and an SNR of 30 from 29.1% to 11.7%. However, the error is largest in the presence of noise and at MTTs that are likely to be encountered in areas of hypoperfusion; furthermore, even though it is reduced, it cannot be corrected for exactly.

Algorithms↗