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PubMed2006

Simplified normal limits and automated quantitative assessment for attenuation-corrected myocardial perfusion SPECT.

BACKGROUND: We aimed to compare normal limits and the detection of coronary artery disease (CAD) with attenuation-corrected (AC) and non-attenuation-corrected (NC) myocardial perfusion single photon emission computed tomography (MPS) by use of a recently improved automated quantification technique. METHODS AND RESULTS: We acquired 415 rest/stress technetium 99m MPS studies on a Vertex dual-detector camera with a gadolinium 153 line source (Vantage Pro). Gender-specific NC, AC, and gender-combined AC normal limits were created from rest/stress images of 50 women and 50 men with a low likelihood of CAD (< 5%) and a median body mass index (BMI) of 30 kg/m2 in each gender group. BMI-specific normal limits (< 30 kg/m2 and > or = 30 kg/m2) were also compared. Total perfusion deficit and 17-segment summed scores in 174 patients were compared with angiography, and normalcy rates were established from 141 studies of low-likelihood patients. There were no differences between low-BMI and high-BMI normal limits for AC or NC studies. Male and female normal limits differed in 12 of 17 segments for NC stress studies and in 3 of 17 segments for AC stress studies (P < .01). The sensitivity, specificity, and normalcy rates for stenoses with 70% narrowing or greater were 89%, 73%, and 91%, respectively, for NC studies and 87%, 80%, and 95%, respectively, for AC studies (P = not significant). CONCLUSION: Automated detection of CAD by AC and NC MPS demonstrated similar sensitivity, specificity, and normalcy rates. Some gender differences were noted for AC normal limits.

Aged↗
PubMed2006

A comparative study of behavioural, physical and mental health status between term-limited and tenure-tracking employees in a population of Japanese male researchers.

OBJECTIVES: Traditional lifelong employment systems have been changing rapidly in Japan. The aim of this study was to assess the health impacts of term-limited employment systems that have recently been introduced into Japanese academic institutes. STUDY DESIGN: Cross-sectional. METHODS: A total of 514 male researchers (275 term limited and 239 tenure track) were compared in terms of behavioural, physical and mental status at annual health examinations. At these examinations, working hours and health-related lifestyles were examined using a self-completed questionnaire. Clinical structured interviews of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) were used to detect major depression. RESULTS: The term-limited researchers tended to work longer hours (P<0.001), drink alcohol more frequently (P<0.001) and eat breakfast less regularly (P<0.001) compared with the tenure-track researchers. Although the prevalence of DSM-IV major depression was comparable (P>0.05) between the two groups, fatigue was more prevalent (P=0.027) in the term-limited researchers than in the tenure-track researchers, adjusting for the effects of age. Compared with colleagues working in the same laboratories, the term-limited researchers worked longer hours, irrespective of fatigue, whereas only the fatigued tenure-track researchers worked longer hours. In the total sample, the fatigued researchers tended to belong to laboratories where their colleagues, on average, worked longer hours, compared with the non-fatigued researchers. CONCLUSIONS: These results imply that the term-limited researchers suffered more from fatigue, due to longer working hours, than their colleagues, and that organized, rather than personal, interventions with respect to the working environment may be effective in reducing overload in such workplaces.

Adult↗
PubMed2006

Comparison of limited and anatomic hepatic resection for hepatocellular carcinoma with hepatitis C.

BACKGROUND: The long-term outcome after resection of hepatocellular carcinoma is influenced by factors related to the tumor and the underlying liver disease. The prognosis of hepatocellular carcinoma is worse in hepatitis C virus antibody-positive patients than in hepatitis B surface antigen-positive patients. In patients with hepatitis C virus infection and hepatocellular carcinoma, the optimum extent of operative resection, i.e., limited versus anatomic, remains controversial. METHODS: Among 247 patients with hepatitis C virus infection who underwent curative resection of hepatocellular carcinoma between 1992 and 2003, 213 patients received limited resection and 34 patients had anatomic resection of at least two Couinaud subsegments with complete removal of the portal territory containing the tumor. The clinical characteristics, operative results, and long-term survival of these two groups were compared. RESULTS: Although the patients receiving limited resection had significantly worse preoperative liver function than the patients undergoing anatomic resection, the postoperative liver function of the limited resection group was significantly better. The mortality and morbidity rates were not significantly different after limited and anatomic resection. Disease-free survival and overall survival were similar after both types of resection, as were the incidence and pattern of intrahepatic tumor recurrence. CONCLUSIONS: In patients with hepatitis C virus infection and hepatocellular carcinoma, anatomic resection does not provide any significant benefit and should not be carried out unless it is technically necessary. In patients with a limited hepatic functional reserve, removal of the tumor with preservation of the liver parenchyma may take priority over wide resection.

Aged↗
PubMed2005

Noticeable, troublesome and objectionable limits of blur.

We investigated limits at which induced blur becomes noticeable, troublesome and objectionable. We used 15 cyclopleged subjects, a Badal optometer with lines of three high contrast letters as targets, 3-6 mm artificial pupils, and 0.0-0.7 logMAR letter sizes. For 0.0 logMAR size, mean "noticeable" blur limits were +/-0.33D, +/-0.30D and +/-0.28D at 3 mm, 4 mm and 6 mm, respectively, but increased by about 70% for 0.7 logMAR letters. All limits reduced by about 17% as pupil size increased from 3 mm to 6 mm. Letter size had a significant influence on all blur limits (1.6-2.1 times), but blur direction had no significant effect. Magnitudes of "troublesome" and 'objectionable" limits were 1.6-1.8 times and 2.1-2.5 times relative to "noticeable" limits, respectively. Our results suggest criteria for troublesome and objectionable blur are relatively unaffected by letter size.

Adolescent↗
PubMed2002

Freeway speed limits and traffic fatalities in Washington State.

BACKGROUND: In 1987 individual states in the USA were allowed to raise speed limits on rural freeways from 55 to 65 mph. Analyses of the impact of the increased speed limits on highway safety have produced conflicting results. OBJECTIVE: To determine if the 1987 speed limit increase on Washington State's rural freeways affected the incidence of fatal crashes or all crashes on rural freeways, or affected average vehicle speeds or speed variance. DESIGN: An ecological study of crashes and vehicle speeds on Washington State freeways from 1974 through 1994. RESULTS: The incidence of fatal crashes more than doubled after 1987, compared with what would have been expected if there had been no speed limit increase, rate ratio 2.1 (95% confidence interval (CI), 1.6-2.7). This resulted in an excess of 26.4 deaths per year on rural freeways in Washington State. The total crash rate did not change substantially, rate ratio 1.1 (95% CI, 1.0-1.3). Average vehicle speed increased by 5.5 mph. Speed variance was not affected by the speed limit increase. CONCLUSIONS: The speed limit increase was associated with a higher fatal crash rate and more deaths on freeways in Washington State.

Accidents, Traffic↗
PubMed2002

Retinal pigment epithelial changes after macular hole surgery with indocyanine green-assisted internal limiting membrane peeling.

PURPOSE: To report the results of macular hole surgery using indocyanine green to improve visualization and facilitate peeling of the internal limiting membrane. METHODS: A retrospective noncomparative review of a consecutive series of 22 patients (22 eyes) who underwent macular hole repair using indocyanine green to facilitate visualization of the internal limiting membrane was performed. One patient was excluded because of a history of a rhegmatogenous retinal detachment. All patients underwent a three-port pars plana vitrectomy with internal limiting membrane peeling. Indocyanine green (0.1% solution) was used to assist in the visualization of the internal limiting membrane. The main outcome measures were postoperative visual acuity, macular hole status, and postoperative retinal pigment epithelial changes. RESULTS: In 21 eyes, the median preoperative best-corrected visual acuity was 20/200 (range, 20/60 to counting fingers at 5 feet). The median postoperative visual acuity was 20/400 (range, 20/60-1/200) with an average follow-up of 13 weeks. The macular hole was closed in 18 eyes (86%) at the most recent follow-up. Ten eyes were found to have atrophic retinal pigment epithelium changes in the area of the previous macular hole. CONCLUSIONS: Indocyanine green assists in visualization of the internal limiting membrane in macular hole surgery. In our series, 10 eyes had unusual atrophic changes in the retinal pigment epithelium at the site of the previous macular hole, or in the area where the indocyanine green solution would have had direct access to the bare retinal pigment epithelium cells. Although the use of indocyanine green improves visualization and assists with peeling of the internal limiting membrane, the safety and potential toxicity of indocyanine green to the retinal pigment epithelium require further investigation.

Aged↗
PubMed2006

Vision-limiting complications in open-globe injuries.

BACKGROUND: To correlate vision-limiting complications of open-globe trauma with anatomical zone and mechanism of injury. METHODS: Retrospective review of 235 patients with open-globe injuries at the Massachusetts Eye and Ear Infirmary. Vision-limiting complications were assessed at 2 to 3 months after the injury. RESULTS: Traumatic cataracts and corneal scarring were the most prevalent vision-limiting complications in patients with zone I (cornea-only) lacerations. The most common vision-limiting factors in eyes with zones II and III lacerations (involving sclera) were cataracts and retinal detachments. In patients with penetrating injuries, predominant vision-limiting findings were traumatic cataracts and corneal scarring. In patients with blunt-force ruptures, leading causes were traumatic cataracts and retinal detachments. There were increased rates of phthisis and enucleation surgery in patients with ruptures and zones II and III injuries. In cases of penetrating and zone I injuries, significantly more patients achieved visual acuities better than 20/50 when compared with eyes that had ruptures or zones II and III injuries. INTERPRETATION: Traumatic cataracts were the most common vision-limiting factor in all subcategories of open-globe injuries. Injuries in zones II and III and blunt-force ruptures were associated with increased rates of retinal detachments, phthisis, and enucleation, contributing to the poorer visual prognosis in these patients.

Adolescent↗
PubMed1999

Indirect reference limits estimated from patients' results by three mathematical procedures.

Presently, only a few clinical laboratories produce their own reference values, while the great majority use reference intervals reported in the literature. An alternative to this unsatisfactory situation is to estimate indirect reference limits by means of mathematical/statistical procedures from patients' results obtained routinely in the laboratory. The procedures of Bhattacharya (A simple method of resolution of a distribution into Gaussian components. Biometrics 1967;23:115-135) Martin et al. (Reference values based on populations accessible to hospitals. In: Gräsbeck R, Alström T, editors. Reference Values in Laboratory Medicine. Chischester: Wiley, 1981:233-262) and Kairisto et al. (Generation of reference values for cardiac enzymes from hospital admission laboratory data. Eur J Clin Chem Clin Biochem 1994;32:789-796) were applied to 14 biochemical quantities. In order to verify these procedures, the indirect reference limits obtained from patients' results were validated by statistical comparison with reference limits estimated from a reference sample according to recommendations of the International Federation of Clinical Chemistry (IFCC). Calculated indirect reference limits for most quantities studied were reliable, but indirect reference limits for bilirubins and potassium ion substance concentrations, alanine aminotransferase, and aspartate aminotransferase catalytic concentrations in serum were not suitable. We conclude that indirect reference limits can be obtained from patients' results by all procedures studied when skewness and kurtosis of mixed distribution are not too large, but other factors also seem to have an influence on the reliability of these procedures.

Adult↗
PubMedDate not supplied

Limitations in activities of daily living: towards a better understanding of subthreshold mental disorders in old age.

Based on a representative sample of elderly subjects, a description of the limitations in activities of daily living (ADL) and instrumental ADL (IADL) at subthreshold levels of dementia and depression is presented and compared against a sample of psychiatric non-cases and samples with specified levels of the respective illnesses. Additionally, it was analyzed whether these limitations are useful diagnostic markers with regard to subdiagnostic psychiatric disorders. Even at subthreshold levels of depression and dementia, elderly people suffer quite extensively from ADL and IADL limitations. However, multifactorial analyses indicate little evidence that these limitations are specific for psychiatric morbidity, be it at subdiagnostic or specified levels. By and large, ADL and IADL limitations in an elderly sample have to be considered instead as consequences of physical health-related comorbidity. Thus, issues regarding the treatment of ADL and IADL limitations at subdiagnostic as well as specified levels of psychiatric morbidity may not be solved from a psychiatric point of view alone, and a multifactorial, i.e., multiprofessional, perspective is strongly recommended.

Activities of Daily Living↗
PubMed1999

Limited ileal resection in infancy: the long-term consequences.

BACKGROUND/PURPOSE: The longer-term sequelae of short bowel syndrome in infancy are reasonably well documented, but little is known about the long-term nutritional and metabolic effects of limited (less than 50 cm) ileal resection. This makes it difficult to formulate a rational follow-up policy in such children. METHODS: All children who underwent limited ileal resection for either necrotizing enterocolitis (NEC) or intussusception at our institution between 1984 and 1992 were invited to attend a detailed clinical, anthropometric, hematologic, and biochemical assessment, together with a biliary and renal ultrasound scan and measurement of bone mineral density. RESULTS: Twenty-four children (NEC, 17; intussusception, 7) of median age 7.4 years (range, 5.5 to 13.7 years) agreed to participate. Nine previously had undergone an isolated ileal resection, and 15 also had had variable lengths of colon removed. The length of resected ileum ranged from 3 to 44 cm, with a median of 10 cm. Seven control subjects in whom neonatal NEC developed but recovered without surgery were also evaluated. Median height, weight, and body mass index after ileal resection were between the 25th and 50th percentiles; no child was stunted or wasted. After ileal resection, one boy was found to have asymptomatic vitamin B12 deficiency, and three children had low plasma concentrations of vitamin A. Hematologic and biochemical parameters were otherwise normal apart from a few marginally low trace element levels in both subjects and controls. No renal calculi were detected, and bone mineral density measurements were normal in all except one child. Four children had cholelithiasis, all of whom had previously undergone limited ileal resection for NEC (two isolated, two ileocolic). Thus, the prevalence of cholelithasis after limited ileal resection for NEC was 24% at a median age of 7.0 years. CONCLUSIONS: Growth and nutritional status are well preserved after limited ileal resection in infancy. Limited ileal resection for NEC is associated with a subsequent high prevalence of cholelithiasis and a risk of vitamin B12 deficiency. These findings are important when planning strategies for long-term follow-up.

Bone Density↗
PubMed2003

An in silico investigation into the causes of telomere length heterogeneity and its implications for the Hayflick limit.

UNLABELLED: In telomerase-negative cell populations the mean telomere length (TL) decreases with increasing population doubling number (PD). A critically small TL is believed to stop cell proliferation at a cell-, age- and species-specific PD thus defining the Hayflick limit. However, positively skewed TL distributions are broad compared to differences between initial and final mean TL and strongly overlap at middle and late PD, which is inconsistent with a limiting role of TL. We used computer-assisted modelling to define what set of premises may account for the above. Our model incorporates the following concepts. DNA end replication problem: telomeres loose 1 shortening unit (SU) upon each cell division. Free radical-caused TL decrease: telomeres experience random events resulting in the loss of a random SU number within a remaining TL. Stochasticity of gene expression and cell differentiation: cells experience random events inducing mitoses or committing cells to proliferation arrest, the latter option requiring a specified number of mitoses to be passed. Cells whose TL reaches 1SU cannot divide. The proliferation kinetics of such virtual cells conforms to the transition probability model of cell cycle. When no committing events occur and at realistic SU estimates of the initial TL, maximal PD values far exceed the Hayflick limit observed in normal cells and are consistent with the crisis stage entered by transformed cells that have surpassed the Hayflick limit. At intermediate PD, symmetrical TL distributions are yielded. Upon introduction of committing events making the ratio of the rates of proliferating and committing events (P/C) range from 1.10 to 1.25, TL distributions at intermediate PD become positively skewed, and virtual cell clones show bimodal size distributions. At P/C as high as 1.25 the majority of virtual cells at maximal PD contain telomeres with TL>1SU. A 10% increase in P/C within the 1.10-1.25 range produces a two-fold increase in the maximal PD, which can reach values of up to 25 observed in rodent and some human cells. Increasing the number of committed mitoses from 0 to 10 can increases PD to about 50 observed in human fibroblasts. Introduction of the random TL breakage makes the shapes of TL distributions quite dissimilar from those observed in real cells. CONCLUSIONS: Telomere length decrease is a correlate of cell proliferation that cannot alone account for the Hayflick limit, which primarily depends on parameters of cell population kinetics. Free radical damage influences the Hayflick limit not through TL but rather by affecting the ratio of the rates of events that commit cells to mitoses or to proliferation arrest.

Animals↗
PubMed1988

Surface-limited growth: a model for the synchronization of a growing bacterial culture through periodic starvation.

This article analyses the Surface-Limited Growth Model put forward to explain the very tight synchrony, over more than ten division cycles, obtained experimentally by subjecting a growing bacterial culture to alternating periods of starvation and dilution, using inorganic phosphate as the limiting substrate. The Model states that when an essential nutrient is in limited supply, the rate of growth of an individual cell will be proportional to its surface area (and the current concentration of the limiting substance) rather than to its volume. This decrease in dimensionality from volume to surface is expected to favor the smaller cells and so result ultimately in a narrower size distribution. The Surface-Limited Growth Model deals with cell growth under unusual nutritional conditions, and its predictions depend on how the cell replication cycle is assumed to behave under these same circumstances. Two alternatives are considered: the volume at which cells divide is the same during the starvation phase as during steady-state exponential growth, and the cells adjust immediately to the changing growth rate. In the latter case, we have tested both C + D constant with time and C + D variable (where C + D is the time between initiation of chromosome replication and the corresponding cell division), the incremental value at any instant being computed separately for each individual cell from its current effective growth rate. The simulation results are of two sorts depending on the auxiliary assumptions used. Either the dilution-starvation cycles have no effect whatsoever on the cell volume distribution, or the width of the distribution decreases gradually with time, approaching zero slowly and asymptotically, but the mean cell volume decreases as well--directly contradicting experimental observations. We conclude that the Surface-Limited Growth Model is incapable of explaining the synchronization of cells by periodic starvation of a growing bacterial culture.

Bacteria↗
PubMed1997

Intentional limited resection for selected patients with T1 N0 M0 non-small-cell lung cancer: a single-institution study.

OBJECTIVES: To comparatively evaluate lobectomy and limited resection for T1 N0 M0 non-small-cell lung cancer, we reviewed case series with concurrent nonrandomized controls. METHODS: Limited resection with curative intent was performed for 63 patients with T1 N0 M0 non-small-cell lung cancer over a 10-year period. These 63 patients included 46 patients who underwent a segmentectomy as an intentional limited resection. These patients had good pulmonary function and could tolerate a lobectomy in the management of their disease. The other 17 patients underwent wedge resection or segmentectomy as a compromised limited resection because they had poor pulmonary reserve or other limiting factors and could withstand a thoracotomy but could not tolerate a lobectomy in the management of their disease. RESULTS: The 5-year survival was 93% in the intentional resection group. The survival curve for this group was not different from that for 77 patients who underwent the standard operation (lobectomy plus complete mediastinal lymph node dissection) for T1 N0 M0 non-small-cell lung cancer during the same period. The frequency of local/regional recurrence in the intentional resection group was 8.7% (4/46); the recurrence in three patients was situated in the mediastinum. According to multivariate analysis, limited resection was not associated with poor survival. CONCLUSION: Segmentectomy with regional lymph node dissection, including the mediastinum, should be considered as an acceptable alternative treatment for selected patients with T1 N0 M0 disease.

Aged↗
PubMed2001

Internal limiting membrane peeling in macular hole surgery.

PURPOSE: To evaluate prospectively the ability to peel epiretinal membranes and to correlate the degree of membrane peeling to anatomic success rates. DESIGN: Consecutive, noncomparative, interventional case series. PARTICIPANTS: One hundred ninety-three patients. METHODS: The extent of membrane peeling and other intraoperative features were correlated to endpoints. MAIN OUTCOME MEASURES: Anatomic success (inducing hole closure), visual acuity of 20/50 or better, and visual improvement of two or more Snellen lines. RESULTS: One hundred ninety-three eyes were eligible for the study by virtue of having a minimum follow-up interval of 6 weeks. The overall anatomic success rate was 93% in these cases. There was a two-line or more improvement in 72%; 56% attained 20/50 or better visual acuity. The internal limiting membrane was peeled completely in 23%, partially in 43%, and not at all in 34%. The degree of internal limiting membrane peeling was not correlated with the duration of the hole or rate of two-line visual improvement, but was inversely correlated with the rate of anatomic success (P = 0.045). Final visual acuity was correlated with a better preoperative visual acuity, shorter preoperative duration of macular hole, and more complete internal limiting membrane peeling. CONCLUSIONS: Peeling of the internal limiting membrane is not essential for anatomic or visual success in macular hole surgery, but it may be a means to standardize inducement of the proper degree of gliosis. Excessive, unsuccessful attempts at internal limiting membrane peeling may decrease visual success. Techniques delivering a more reproducible, complete, atraumatic peeling of the internal limiting membrane should be studied.

Epiretinal Membrane↗
PubMed1999

Functional activity of hepatocyte nuclear factor-1 is specifically decreased in amino acid-limited hepatoma cells.

Limitation of cultured rat hepatoma cells for an essential amino acid results in a specific decrease in expression of several genes that are preferentially expressed in the liver, including the serum albumin and transthyretin genes. In the work presented here, we examined whether the coordinate repression of these genes is caused by decreased activity of one or more of the liver-enriched transcription factors, hepatocyte nuclear factor-1 (HNF-1), HNF-3, HNF-4 or C/EBP. To address this question, HepG2 human hepatoma cells were transiently transfected with luciferase reporter constructs containing multiple copies of individual transcription factor binding sites. Limitation for an essential amino acid resulted in specific repression of a construct in which luciferase expression was directed by HNF-1. A single HNF-1 binding site located adjacent to the TATA box plays a major role in transcription directed by the serum albumin promoter in transient transfection assays. Amino acid limitation of cells transfected with an albumin promoter/luciferase reporter construct resulted in specific repression of promoter activity. In addition, bacterial methylation or site-directed mutagenesis of the HNF-1 binding site in the albumin proximal promoter region eliminated the regulation of an albumin promoter-luciferase reporter construct under conditions of amino acid limitation. These results demonstrated that the HNF-1 binding site played a major role in regulation of the albumin promoter by amino acid availability. Deletion analysis of the albumin promoter confirmed regulation through the HNF-1 binding site and also identified a second amino acid regulatory element in the upstream region of the albumin promoter, which has been shown previously to contain a functional binding site for HNF-3. The repression of albumin promoter and HNF-1 reporter constructs in amino acid-limited cells occurred without a change in the DNA binding activity of HNF-1. Moreover, HNF-3 DNA binding activity was also not decreased in amino acid-limited cells. These results suggest that the regulation of transcription by amino acids occurs at the level of transcriptional activation by HNF-1 and HNF-3, rather than by alteration of the DNA binding activity of either factor.

Amino Acids↗
PubMed2002

Choosing an equivalence limit for noninferiority or equivalence studies.

Studies that compare treatments with the purpose of demonstrating that the treatments are similar require an a priori definition of an equivalence limit, how different the treatments can be before the difference is of concern. Defining such an equivalence limit is one of the most difficult aspects of planning the study. Three principles are proposed for setting such limits, depending on the objective of the study: a putative placebo calculation, an approach based on clinically important differences, and methods based on statistical properties. All methods will be useful for many studies, but the study objective should determine the final choice of an equivalence limit. The statistician must play an integral role in determining the final equivalence limit. Advice is offered for helping the statistician participate in the decision on the equivalence limits.

Clinical Trials as Topic↗
PubMed2003

Mobility limitations 1974-1991: period changes explaining improvement in the population.

The proportion of people with mobility limitations (difficulties with running, walking and stairs) decreased between 1968 and 1991 in the Swedish population aged 18-75. The distribution of predictors of late life morbidity, e.g., social class, health behaviour and childhood conditions, also changed during this period. This study explored whether the changes in these predictors over time were related to the decrease in the proportion of the population with mobility limitations. In two nationally representative interview samples (n=4468) from 1974 and 1991 of persons aged 45-71 the odds for limitations were cross-sectionally compared in ordered logistic regression models. In addition, predictors for the mobility outcome in 1974 were collected from an earlier 1968 survey and predictors for the 1991 outcome were collected from 1981. In 1974 the odds for limitations in the population was 50% higher than in 1991. Had the population composition regarding social class and housewives in 1991 been identical to 1974, the odds for limitations would have been similar in 1974 and 1991. Period improvement in social classes with poorer mobility also contributed to the overall period improvement. Health behaviours were examined as possible mediating factors. The increase of physically active people between 1968 and 1974 was related to the period improvement in mobility between 1974 and 1991. Smoking showed an increased association with mobility limitations during the period, indicating that mobility improvement would have been greater if everyone had been a non-smoker. Results indicate how sensitive disability rates may be for cohort or period effects.

Adolescent↗
PubMed2002

Limited-data image registration for radiotherapy positioning and verification.

PURPOSE: One benefit to having on-line CT imaging integrated into a radiotherapy system is that images can be collected with the patient in the treatment position. These images can then be automatically registered to planning images for improved positioning and verification. However, many such on-line imaging systems have a limited field of view (LFOV) that could potentially impair registration. Thus, the viability of automatic registration was investigated in the context of collecting on-line LFOV and also limited-slice CT images for radiotherapy. METHODS AND MATERIALS: Mutual information and two new voxel-based registration algorithms were tested to align LFOV and limited-slice prostate and breast images given known displacements. Success rates were tallied for different field-of-view sizes, slice distributions, and initial displacements. RESULTS: Most of the automatic registration algorithms tested were useful for solving these LFOV and limited-slice problems. Registration of LFOV images was generally successful, especially for fields of view of at least half the patient's size. For limited-slice images, success was more closely correlated to the slice spacing than to the number of slices used, with sparse slice spacing being preferable. CONCLUSIONS: Mutual information and other automatic registration algorithms have been identified as useful methods for registering LFOV and limited-slice radiotherapy images with planning CT images.

Algorithms↗