Biomedical subjects
Publications and source records attributed to M Brambilla.
We have observed optical patterns in GaAs/GaAlAs vertical-cavity microresonators. Rolls, rhombs, or hexagons were obtained depending on the wavelength detuning. We show that cavity thickness fluctuations contribute to pattern selection.
We apply a versatile numerical technique to establishing the existence of cavity solitons (CS) in a semiconductor microresonator with bulk GaAs or multiple quantum well GaAs/AlGaAs as its active layer. Based on a Newton method, our approach implies the evaluation of the linearized operator describing deviations from the exact stationary state. The eigenvalues of this operator determine the dynamical stability of the CS. A typical eigenspectrum contains a zero eigenvalue with which a "neutral mode" of the CS is associated. Such neutral modes are characteristic of models with translational symmetry. All other eigenvalues typically have negative real parts large enough to cause any excitations to die out in a few medium response times. The neutral mode thus dominates the response to external random or deterministic perturbations, and its excitation induces a simple translation of the CS, which are thus stable and robust. We show how to relate the speed with which a CS moves under external perturbations to the projection of the perturbations on to the neutral mode, and give some examples, including weak gradients on the driving field and interaction with other CS. Finally, we show that the separatrix between two stable coexisting solutions: the homogeneous solution and the CS is the intervening unstable CS solution. Our results are important with a view to future applications of CS to optical information processing.
BACKGROUND: An optimal use and exploitation of professional personnel is of paramount importance for health management organizations, as human resources are both their greatest asset and heaviest financial burden. To better understand the amount of medic and paramedic work and time required for the typical diagnostic and therapeutic procedures in a coronary-care unit setting, we measured their average times and analyzed their inherent co-factors. METHODS: This study was conducted on 206 consecutive coronary-care unit patients. These patients were divided into subgroups according to their admission diagnosis: acute myocardial infarction, unstable angina, acute cardiac failure, pulmonary embolism or other pathologies. Each subgroup was then subdivided even further according to the severity of their clinical status. Diagnostic and therapeutic procedures ("macroactivities") have been identified and each one was subdivided into sub-procedures ("microactivities"). All microactivities were carefully clocked in every patient in order to calculate the average execution time for every macroactivity. RESULTS: Our data show that myocardial infarction patients and, in general, a more severe clinical status required a longer stay in the coronary-care unit. Again, longer overall clinical performance times were necessary in myocardial infarction patients as compared to the unstable angina subgroup. There were no statistically significant differences among other subgroups. More severely ill patients required longer clinical performance times because of both a longer coronary-care unit stay and longer clinical performance time per day. More than half of the total clinical performance time for each patient was spent during the first two days. Paramedics supplied more than 80% of the total performance time. CONCLUSIONS: The authors undertook a study of typical coronary-care unit clinical activities by clocking the performance times of the usual diagnostic and therapeutic procedures. The data thus obtained come from direct measurements and describe the clinical performance of both medics and paramedics in a real-life setting. This could thus be used as a yardstick to verify current workload standards. It is hoped that a deeper understanding of these activities will optimize the full exploitation of available human resources.
The aim of this study was to determine the diagnostic accuracy of technetium-99m tetrofosmin myocardial imaging for the localization of coronary artery stenoses of different degrees of severity. Stress-rest single-photon emission tomography (SPET) was performed on separate days in 80 patients (64 males, 16 females; mean age 61 years; 43 patients with previous myocardial infarction; 18 patients with pharmacological stress), within 6 months of coronary angiography. Scintigraphic images were blindly and independently evaluated by three observers. Coronary stenosis was defined as a >50% narrowing in luminal diameter; severe stenosis was defined as a proximal stenosis of >75% or a peripheral stenosis of >90%. Coronary angiography revealed normal coronary arteries or insignificant coronary stenosis in 13 patients and significant coronary stenoses in 67 patients. The sensitivity and specificity of 99mTc-tetrofosmin SPET in respect of severely stenosed vessels were, respectively, 80% and 65% for the left anterior descending artery (LAD), 100% and 46% for the right coronary artery (RCA) and 58 and 78% for the left circumflex artery (LCx) territories. Considering all the significantly stenosed vessels, a significant decrease in sensitivity was observed for LAD territories (to 59%, P=0.05), and a nonsignificant decrease for RCA (88%) and LCx (47%) territories while specificity values remained essentially unchanged. No significant changes in sensitivity or specificity were observed when regions with previous myocardial infarction were excluded. In conclusion, the sensitivity of 99mTc-tetrofosmin SPET for the localization of individual stenosed vessels is only moderate when all significant stenoses are considered, but the ability of this technique to predict the location of severe coronary artery stenoses seems satisfactory, with the exception of the low specificity in respect of RCA territories.
UNLABELLED: The purpose of this study was to evaluate the feasibility of a shorter method of performing platelet kinetic studies with respect to the conventional 8-9-day approach. METHODS: We studied 41 patients (28 women, 13 men; mean age 52 yr) with primary idiopathic thombocytopenic purpura (ITP) (n = 20), secondary ITP (n = 9), HCV associated thrombocytopenia (n = 9), splenectomy (n = 1) and hairy-cell leukemia (n = 1). The patients were in a steady-state of platelet turnover. Initial platelet counts ranged from 19 to 302 x 10(9)/liter (mean value = 83). Platelet survival times (PST) were measured from the blood radioactivity disappearance curve of 111In-oxine-labeled autologus platelets following the recommendations of the International Committee for Standardization in Haematology: blood samples were taken at 30 min and 2 and 4 hr and thereafter daily for 7 days. PST was calculated by the weighted mean method and ranged from 18 to 219 hr (mean value = 98). PST was also calculated using only the data collected at 2, 48 and 96 hr. If the radioactivity in the blood at 96 hr exceeded 10% of the 2-hr value, the additional point at 168 hr was used. RESULTS: By using this reduced dataset, we obtained a correlation of r = 0.97 with the PST obtained from the whole dataset. In 24 patients, the difference was between +/- 10 hr and exceeded 1 day in only 4. CONCLUSION: About 94% of the data may be recovered with only three or four blood samples and the duration may be shortened to 4 days in a significant proportion of patients (48% of ITP patients). This approach offers the advantages of increased patient throughput, compliance and reduced examination costs.
For the development and validation of a quantitative approach to the analysis of bone scans after total knee arthroplasty, 39 consecutive patients with 40 prostheses (6 males, 33 females; mean age, 70 years) were scheduled for clinical, radiographic, and scintigraphic examination ranging from 9 to 90 months after surgery. Twenty-seven total knee arthroplasties were considered to be asymptomatic and 13 symptomatic according to the clinical and radiographic findings. Significant differences were found for 99mTc-methylene diphosphonate uptake for femur and tibia and between symptomatic and asymptomatic patients. A reference range was determined for radionuclide uptake in the periprosthetic bone of the 27 asymptomatic total knee arthroplasties; this range was then used to identify loose total knee arthroplasties among the 13 symptomatic knees. With a clinical and radiographic followup performed 1 year after scintigraphy as a standard of comparison, a sensitivity of 88% (7/8) and a specificity of 100% (5/5) was demonstrated. These preliminary results suggest the feasibility of a quantitative approach to the scintigraphic evaluation of total knee arthroplasties after the first postsurgical year.
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Recent reports suggest that radionuclide bone scan (BS) may not be necessary in the standard staging evaluation of patients with prostate cancer when serum prostate-specific antigen (PSA) levels are normal. To evaluate the ability of PSA to predict BS findings, we retrospectively reviewed the case records of 118 consecutive patients (median age 73 years, range 50-90 years) with newly diagnosed, untreated, pathologically proven prostate cancer who underwent BS and serum PSA sampling within a period of no more than 3 months. Fifty-four out of 118 BSs demonstrated metastatic bone disease. A PSA value of less than 10 ng/ml excluded bone metastasis; of 35 patients with a serum PSA level of 20 ng/ml or less, seven had a positive BS (negative predictive value of 80%). These findings provide additional confirmation of the value of low serum PSA concentrations in excluding the need for a staging BS, although the threshold for a high value of negative predictive accuracy is lower than previously reported.
The lung uptake of thallium-201 (201Tl) in planar imaging was evaluated in 384 patients enrolled in the SIRT study (Italian Multicentre Study on Thallium Reinjection). All patients underwent treadmill exercise, and at peak exercise 74 MBq of 201TI were injected. The patients were then evaluated after reinjection of 201Tl under baseline conditions. The left ventricle was subdivided into 16 echocardiographic and 15 scintigraphic segments. The best correlates of visually scored 201Tl lung uptake, of the lung heart ratio and lung wash-out were checked. The independent variables entered in the stepwise multiple-regression analysis were: the echocardiographic wall motion index, the scintigraphic perfusion score index, and the number of segments that improved by at least 1 and 2 grades after redistribution and after reinjection. We concluded that the lung:heart ratio and, in particular, lung wash-out do not correlate more closely than the visual score with the variables taken into consideration. This suggests that visually scored lung uptake of 201Tl is still of value in nuclear cardiology practice. The scintigraphic variables associated with reinjection do not seem to offer any additional information with respect to redistribution variables. We also analysed the impact on 201Tl lung uptake of several other index variables. Student's t-test revealed that no single variable significantly alters lung uptake after stress testing.
UNLABELLED: To establish the real nature of 201Tl defects in the assessment of myocardial viability (e.g., fixed versus reversible), 201Tl reinjection was evaluated in a multicenter trial involving 402 consecutive patients with ischemic heart disease and exercise 201Tl defects. METHODS: Twelve hospitals, using the same type of gamma camera and computer software, adopted one of the two most widely used reinjection protocols. In 230 patients (Group A), reinjection was performed immediately after stress-redistribution planar imaging; in 172 patients (Group B), reinjection was performed on a separate day and followed by rest-redistribution imaging. The images were interpreted by three blinded observers in a core laboratory on a five-point qualitative scale; the reproducibility in visual scoring was excellent. RESULTS: Groups A and B had a similar prevalence of myocardial segments with abnormal uptake at stress (39%, 40%), as well as with reversible (16%, 17%), partially reversible (21%, 19%) and irreversible (63%, 64%) defects at redistribution. After reinjection, 201Tl uptake improved in 27% and 36% of both partially reversible and irreversible defects in Groups A and B. No differences were found when comparing early and delayed reinjection imaging in Group B. CONCLUSION: This study confirms the validity of 201Tl reinjection in a large, unselected population, but the discordance with stress/redistribution is less than has been previously reported for both 201Tl reinjection protocols, the prevalence of improved segments after reinjection was higher with the separate day approach.
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UNLABELLED: Inter- and intraobserver reproducibility (R) of segmental 201Tl scores after stress (ST), redistribution (RD) and reinjection (RI) planar imaging were evaluated. METHODS: Images were examined from 396 patients with suspected coronary artery disease, demonstrated by means of post-ST imaging of at least one perfusion defect. To eliminate external sources of variability, the same gamma camera, acquisition protocol and computer software were used in this multicenter study. Thallium-201 images of the anterior, left anterior oblique and left lateral projections were obtained immediately, 4 hr after exercise and 30 min after the injection of additional 201Tl either on the same day or on a different day. The left ventricle was divided into 15 segments and evaluated by three independent observers, blinded to clinical data, according to a five-point scale. RESULTS: The R score for ST, RD and RI images, expressed as an intraclass correlation coefficient, was 0.76, 0.74 and 0.72, respectively. After averaging multiple observer scores, R increased to 0.91, 0.90 and 0.89, respectively. Individual observer measurement of the R score was 0.48, 0.51 and 0.32 for ST-RD, ST-RI and RD-RI image pairs, respectively, and multiple observer scores showed R increases to 0.74, 0.76 and 0.58. CONCLUSION: This qualitative scale reliably assesses the severity of 201Tl perfusion defects, particularly when multiple-observer scores are averaged. Individual observer change scores should be taken with great caution, especially in studies involving the visual evaluation of RD-RI image changes.
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Using a spectrophotometer with an internal integrating sphere, the absorption (mu a) and reduced scattering (mu s') coefficients of in vitro epidermis were evaluated from reflectance and transmittance measurements. mu a and mu s' varied from 24 to 0.2 cm-1, and from 32 to 21 cm-1 respectively, on passing from 400 to 800 nm. Moreover, using an external integrating sphere, the reflectance spectrum of in vivo skin was compared with the reflectance spectrum calculated with a Monte Carlo model, in which the mean values of mu a and mu s' and different anisotropy parameters were used as input data. In vivo results show that the principle of similarity is entirely valid for wavelengths greater than 600 nm and may be considered a good approximation in the 400-600 nm band, and suggest that optical characteristics of in vivo skin may be inferred from reflectance measurements.
In an attempt to evaluate whether induced fluorescence could be exploited to discriminate neoplastic from non-neoplastic tissue, fluorescence spectroscopy was performed at 450-800 nm on 83 biopsy specimens of colonic mucosa. Measurements showed that fluorescence spectra of adenoma, adenocarcinoma and non-neoplastic mucosa manifest dissimilar patterns. Nine variables, whose photophysical and/or biological bases need further investigation, were derived from the spectra. Discriminant functions between the groups of lesions were determined by using a stepwise discriminant analysis. The diagnostic test had a sensitivity of 80.6% and 88.2%, and a specificity of 90.5% and 95.2% in discriminating neoplastic from non-neoplastic mucosa and adenoma from non-neoplastic mucosa respectively. These results suggest that fluorescence spectroscopy has the potential to improve endoscopic diagnosis of premalignant and malignant lesions of colonic mucosa.
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