A study of high frequency ultrasound scattering from non-nucleated biological specimens.

The high frequency backscatter from cells with a nucleus to cell volume ratio of 0.50 cannot be adequately modeled as a homogeneous sphere. It was hypothesized that the cytoplasm of such cells is of fluid nature. This work attempts to model the ultrasound backscatter (10-62 MHz) from some non-nucleated biological specimens. This was done by measuring the backscatter response from individual sea urchin oocytes and comparing it to theoretical predictions in both the time and frequency domains. A good agreement was found between the experimental and theoretical results suggesting that the non-nucleated oocytes are of fluid nature.

The fluid and elastic nature of nucleated cells: implications from the cellular backscatter response.

In a previous experiment [Baddour et al., J. Acoust. Soc. Am. 117(2), 934-943 (2005)] it was shown that it is possible to deduce the ultrasound backscatter transfer function from single, subresolution cells in vitro, across a broad, continuous range of frequencies. Additional measurements have been performed at high frequencies (10-65 MHz) on cells with different relative nucleus sizes. It was found that for cells with a nucleus to cell volume ratio of 0.50, the backscatter response was better modeled as an elastic sphere. For the cells in which the ratio was 0.33, the backscatter showed good agreement with the theoretical solution for a fluid sphere.

Ultrasonic characterization of whole cells and isolated nuclei.

High frequency ultrasound imaging (20 to 60 MHz) is increasingly being used in small animal imaging, molecular imaging and for the detection of structural changes during cell and tissue death. Ultrasonic tissue characterization techniques were used to measure the speed of sound, attenuation coefficient and integrated backscatter coefficient for (a) acute myeloid leukemia cells and corresponding isolated nuclei, (b) human epithelial kidney cells and corresponding isolated nuclei, (c) multinucleated human epithelial kidney cells and d) human breast cancer cells. The speed of sound for cells varied from 1522 to 1535 m/s, while values for nuclei were lower, ranging from 1493 to 1514 m/s. The attenuation coefficient slopes ranged from 0.0798 to 0.1073 dB mm(-1) MHz(-1) for cells and 0.0408 to 0.0530 dB mm(-1) MHz(-1) for nuclei. Integrated backscatter coefficient values for cells and isolated nuclei showed much greater variation and increased from 1.71 x 10(-4) Sr(-1) mm(-1) for the smallest nuclei to 26.47 x 10(-4) Sr(-1) mm(-1) for the cells with the largest nuclei. The findings suggest that integrated backscatter coefficient values, but not attenuation or speed of sound, are correlated with the size of the nuclei.

High-frequency ultrasound assessment of antimicrobial photodynamic therapy in vitro.

Ultrasound imaging is proving to be an important tool for medical diagnosis of dermatological disease. Backscatter spectral profiles using high-frequency ultrasound (HFUS, 10-100 MHz) are sensitive to subtle changes in eukaryotic cellular morphology and mechanical properties that are indicative of early apoptosis, the main type of cell death induced following photodynamic therapy (PDT). We performed experiments to study whether HFUS could also be used to discern changes in bacteria following PDT treatment. Pellets of planktonic Staphylococcus aureus were treated with different PDT protocols and subsequently interrogated with HFUS. Changes in ultrasound backscatter response were found to correlate with antimicrobial effect. Despite their small size, distinct changes in bacterial morphology that are indicative of cell damage or death are detectable by altered backscatter spectra from bacterial ensembles using HFUS. This highlights the potential for HFUS in rapidly and non-invasively assessing the structural changes related to antimicrobial response.

A comparison of Canadian medical students from rural and non-rural backgrounds.

CONTEXT: Very little is known about medical students from rural areas currently enrolled in Canadian medical schools. PURPOSE: We aimed to compare rural and non-rural students in terms of demographics, socioeconomic status, financial status and career choices. METHODS: As part of a larger Internet survey of all students at Canadian medical schools outside Quebec, conducted in January and February 2001, we conducted post-hoc analyses to compare students from rural and non-rural areas. Canada Post's classification system was used to determine rural status. To compare differences between rural and non-rural students, we used logistical regression models for categorical variables and factorial analysis of variance for continuous variables. RESULTS: We received responses from 2994 (68.5%) of 4368 medical students. Eleven percent of Canadian medical students come from rural backgrounds. Rural students tend to be older and originate from families of lower socioeconomic status. Students from rural areas report higher levels of debt, increased rates of paid part-time and summer employment, and greater stress from their finances. Nevertheless, rural students are not more likely to state that financial considerations will affect their choice of specialty or practice location. CONCLUSIONS: Canadian medical students who come from rural backgrounds are different from their non-rural counterparts. Students from rural areas face numerous financial barriers in obtaining a medical education and report greater levels of financial stress. Medical schools should examine and address barriers to admission of rural students and they should consider directing more financial resources toward this financially vulnerable group.

Effects of rising tuition fees on medical school class composition and financial outlook.

BACKGROUND: Since 1997, tuition has more than doubled at Ontario medical schools but has remained relatively stable in other Canadian provinces. We sought to determine whether the increasing tuition fees in Ontario affected the demographic characteristics and financial outlook of medical students in that province as compared with those of medical students in the rest of Canada. METHODS: As part of a larger Internet survey of all students at Canadian medical schools outside Quebec, conducted in January and February 2001, we compared the respondents from Ontario schools with those from the other schools (control group). Respondents were asked about their age, sex, self-reported family income (as a direct indicator of socioeconomic status), the first 3 digits of their postal code at graduation from high school (as an indirect indicator of socioeconomic status), and importance of financial considerations in choosing a specialty and location of practice. We used logistic regression models to see if temporal changes (1997 v. 2000) among Ontario medical students differed from those among medical students elsewhere in Canada apart from Quebec. RESULTS: Responses were obtained from 2994 (68.5%) of 4368 medical students. Across the medical schools, there was an increase in self-reported family income between 1997 and 2000 (p = 0.03). In Ontario, the proportion of respondents with a family income of less than $40,000 declined from 22.6% to 15.0%. However, compared with the control respondents, the overall rise in family income among Ontario students was not statistically significant. First-year Ontario students reported higher levels of expected debt at graduation than did graduating students (median $80,000 v. $57,000) (p < 0.001), and the proportion of students expecting to graduate with debt of at least $100,000 more than doubled. Neither of these differences was observed in the control group. First-year Ontario students were also more likely than fourth-year Ontario students to report that their financial situation was "very" or "extremely" stressful and to cite financial considerations as having a major influence on specialty choice or practice location. These differences were not observed in the control group. INTERPRETATION: At Canadian medical schools, there are fewer students from low-income families in general. However, Ontario medical students report a large increase in expected debt on graduation, an increased consideration of finances in deciding what or where to practise, and increasing financial stress, factors that are not observed among students in other provinces.

Characteristics of first-year students in Canadian medical schools.

BACKGROUND: The demographic and socioeconomic profile of medical school classes has implications for where people choose to practise and whether they choose to treat certain disadvantaged groups. We aimed to describe the demographic and socioeconomic characteristics of first-year Canadian medical students and compare them with those of the Canadian population to determine whether there are groups that are over- or underrepresented. Furthermore, we wished to test the hypothesis that medical students often come from privileged socioeconomic backgrounds. METHODS: As part of a larger Internet survey of all students at Canadian medical schools outside Quebec, conducted in January and February 2001, first-year students were asked to give their age, sex, self-described ethnic background using Statistics Canada census descriptions and educational background. Postal code at the time of high school graduation served as a proxy for socioeconomic status. Respondents were also asked for estimates of parental income and education. Responses were compared when possible with Canadian age-group-matched data from the 1996 census. RESULTS: Responses were obtained from 981 (80.2%) of 1223 first-year medical students. There were similar numbers of male and female students (51.1% female), with 65% aged 20 to 24 years. Although there were more people from visible minorities in medical school than in the Canadian population (32.4% v. 20.0%) (p < 0.001), certain minority groups (black and Aboriginal) were underrepresented, and others (Chinese, South Asian) were overrepresented. Medical students were less likely than the Canadian population to come from rural areas (10.8% v. 22.4%) (p< 0.001) and were more likely to have higher socioeconomic status, as measured by parents' education (39.0% of fathers and 19.4% of mothers had a master's or doctoral degree, as compared with 6.6% and 3.0% respectively of the Canadian population aged 45 to 64), parents' occupation (69.3% of fathers and 48.7% of mothers were professionals or high-level managers, as compared with 12.0% of Canadians) and household income (15.4% of parents had annual household incomes less than $40,000, as compared with 39.7% of Canadian households; 17.0% of parents had household incomes greater than $160,000, as compared with 2.7% of Canadian households with an income greater than $150,000). Almost half (43.5%) of the medical students came from neighbourhoods with median family incomes in the top quintile (p < 0.001). A total of 57.7% of the respondents had completed 4 years or less of postsecondary studies before medical school, and 29.3% had completed 6 or more years. The parents of the medical students tended to have occupations with higher social standing than did working adult Canadians; a total of 15.6% of the respondents had a physician parent. INTERPRETATION: Canadian medical students differ significantly from the general population, particularly with regard to ethnic background and socioeconomic status.