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Biomedical subjects

J M Fitzpatrick

Publications and source records attributed to J M Fitzpatrick.

At least 73 records · Page 4Linked to original sources
PubMed1998

Measurement of intraoperative brain surface deformation under a craniotomy.

OBJECTIVE: Several causes of spatial inaccuracies in image-guided surgery have been carefully studied and documented for several systems. These include error in identifying the external features used for registration, geometrical distortion in the preoperative images, and error in tracking the surgical instruments. Another potentially important source of error is brain deformation between the time of imaging and the time of surgery or during surgery. In this study, we measured the deformation of the dura and brain surfaces between the time of imaging and the start of surgical resection for 21 patients. METHODS: All patients underwent intraoperative functional mapping, allowing us to measure brain surface motion at two times that were separated by nearly an hour after opening the dura but before performing resection. The positions of the dura and brain surfaces were recorded and transformed to the coordinate space of a preoperative magnetic resonance image, using the Acustar surgical navigation system (manufactured by Johnson & Johnson Professional, Inc., Randolph, MA) (the Acustar trademark and associated intellectual property rights are now owned by Picker International, Highland Heights, OH). This system performs image registration with bone-implanted markers and tracks a surgical probe by optical triangulation. RESULTS: The mean displacements of the dura and the first and second brain surfaces were 1.2, 4.4, and 5.6 mm, respectively, with corresponding mean volume reductions under the craniotomy of 6, 22, and 29 cc. The maximum displacement was greater than 10 mm in approximately one-third of the patients for the first brain surface measurement and one-half of the patients for the second. In all cases, the direction of brain shift corresponded to a "sinking" of the brain intraoperatively, compared with its preoperative position. Analysis of the measurement error revealed that its magnitude was approximately 1 to 2 mm. We observed two different patterns of the brain surface deformation field, depending on the inclination of the craniotomy with respect to gravity. Separate measurements of brain deformation within the closed cranium caused by changes in patient head orientation with respect to gravity suggested that less than 1 mm of the brain shift recorded intraoperatively could have resulted from the change in patient orientation between the time of imaging and the time of surgery. CONCLUSION: These results suggest that intraoperative brain deformation is an important source of error that needs to be considered when using surgical navigation systems.

Adult↗
PubMed1998

Visual assessment of the accuracy of retrospective registration of MR and CT images of the brain.

In a previous study we demonstrated that automatic retrospective registration algorithms can frequently register magnetic resonance (MR) and computed tomography (CT) images of the brain with an accuracy of better than 2 mm, but in that same study we found that such algorithms sometimes fail, leading to errors of 6 mm or more. Before these algorithms can be used routinely in the clinic, methods must be provided for distinguishing between registration solutions that are clinically satisfactory and those that are not. One approach is to rely on a human observer to inspect the registration results and reject images that have been registered with insufficient accuracy. In this paper, we present a methodology for evaluating the efficacy of the visual assessment of registration accuracy. Since the clinical requirements for level of registration accuracy are likely to be application dependent, we have evaluated the accuracy of the observer's estimate relative to six thresholds: 1-6 mm. The performance of the observers was evaluated relative to the registration solution obtained using external fiducial markers that are screwed into the patient's skull and that are visible in both MR and CT images. This fiducial marker system provides the gold standard for our study. Its accuracy is shown to be approximately 0.5 mm. Two experienced, blinded observers viewed five pairs of clinical MR and CT brain images, each of which had each been misregistered with respect to the gold standard solution. Fourteen misregistrations were assessed for each image pair with misregistration errors distributed between 0 and 10 mm with approximate uniformity. For each misregistered image pair each observer estimated the registration error (in millimeters) at each of five locations distributed around the head using each of three assessment methods. These estimated errors were compared with the errors as measured by the gold standard to determine agreement relative to each of the six thresholds, where agreement means that the two errors lie on the same side of the threshold. The effect of error in the gold standard itself is taken into account in the analysis of the assessment methods. The results were analyzed by means of the Kappa statistic, the agreement rate, and the area of receiver-operating-characteristic (ROC) curves. No assessment performed well at 1 mm, but all methods performed well at 2 mm and higher. For these five thresholds, two methods agreed with the standard at least 80% of the time and exhibited mean ROC areas greater than 0.84. One of these same methods exhibited Kappa statistics that indicated good agreement relative to chance (Kappa > 0.6) between the pooled observers and the standard for these same five thresholds. Further analysis demonstrates that the results depend strongly on the choice of the distribution of misregistration errors presented to the observers.

Algorithms↗
PubMed1998

Predicting error in rigid-body point-based registration.

Guidance systems designed for neurosurgery, hip surgery, and spine surgery, and for approaches to other anatomy that is relatively rigid can use rigid-body transformations to accomplish image registration. These systems often rely on point-based registration to determine the transformation, and many such systems use attached fiducial markers to establish accurate fiducial points for the registration, the points being established by some fiducial localization process. Accuracy is important to these systems, as is knowledge of the level of that accuracy. An advantage of marker-based systems, particularly those in which the markers are bone-implanted, is that registration error depends only on the fiducial localization error (FLE) and is thus to a large extent independent of the particular object being registered. Thus, it should be possible to predict the clinical accuracy of marker-based systems on the basis of experimental measurements made with phantoms or previous patients. This paper presents two new expressions for estimating registration accuracy of such systems and points out a danger in using a traditional measure of registration accuracy. The new expressions represent fundamental theoretical results with regard to the relationship between localization error and registration error in rigid-body, point-based registration. Rigid-body, point-based registration is achieved by finding the rigid transformation that minimizes "fiducial registration error" (FRE), which is the root mean square distance between homologous fiducials after registration. Closed form solutions have been known since 1966. The expected value (FRE2) depends on the number N of fiducials and expected squared value of FLE, (FLE-2, but in 1979 it was shown that (FRE2) is approximately independent of the fiducial configuration C. The importance of this surprising result seems not yet to have been appreciated by the registration community: Poor registrations caused by poor fiducial configurations may appear to be good due to a small FRE value. A more critical and direct measure of registration error is the "target registration error" (TRE), which is the distance between homologous points other than the centroids of fiducials. Efforts to characterize its behavior have been made since 1989. Published numerical simulations have shown that (TRE2) is roughly proportional to (FLE2)/N and, unlike (FRE2), does depend in some way on C. Thus, FRE, which is often used as feedback to the surgeon using a point-based guidance system, is in fact an unreliable indicator of registration-accuracy. In this work we derive approximate expressions for (TRE2), and for the expected squared alignment error of an individual fiducial. We validate both approximations through numerical simulations. The former expression can be used to provide reliable feedback to the surgeon during surgery and to guide the placement of markers before surgery, or at least to warn the surgeon of potentially dangerous fiducial placements; the latter expression leads to a surprising conclusion: Expected registration accuracy (TRE) is worst near the fiducials that are most closely aligned! This revelation should be of particular concern to surgeons who may at present be relying on fiducial alignment as an indicator of the accuracy of their point-based guidance systems.

Humans↗
PubMed1998

Surface-based registration of CT images to physical space for image-guided surgery of the spine: a sensitivity study.

This paper presents a method designed to register preoperative computed tomography (CT) images to vertebral surface points acquired intraoperatively from ultrasound (US) images or via a tracked probe. It also presents a comparison of the registration accuracy achievable with surface points acquired from the entire posterior surface of the vertebra to the accuracy achievable with points acquired only from the spinous process and central laminar regions. Using a marker-based method as a reference, this work shows that submillimetric registration accuracy can be obtained even when a small portion of the posterior vertebral surface is used for registration. It also shows that when selected surface patches are used, CT slice thickness is not a critical parameter in the registration process. Furthermore, the paper includes qualitative results of registering vertebral surface points in US images to multiple CT slices. The method has been tested with US points and physical points on a plastic spine phantom and with simulated data on a patient CT scan.

Humans↗
PubMed1998

Registration of head CT images to physical space using a weighted combination of points and surfaces.

Most previously reported registration techniques that align three-dimensional image volumes by matching geometrical features such as points or surfaces use a single type of feature. We recently reported a hybrid registration technique that uses a weighted combination of multiple geometrical feature shapes. In this study we use the weighted geometrical feature (WGF) algorithm to register computed tomography (CT) images of the head to physical space using the skin surface only, the bone surface only, and various weighted combinations of these surfaces and one fiducial point (centroid of a bone-implanted marker). We use data acquired from 12 patients that underwent temporal lobe craniotomies for the resection of cerebral lesions. We evaluate and compare the accuracy of the registrations obtained using these various approaches by using as a reference gold standard the registration obtained using three bone-implanted markers. The results demonstrate that a combination of geometrical features can improve the accuracy of CT-to-physical space registration. Point-based registration requires a minimum of three noncolinear points. The position of a bone-implanted marker can be determined much more accurately than that of a skin-affixed marker or an anatomic landmark. A major disadvantage of using bone-implanted markers is that an invasive procedure is required to implant each marker. By combining surface information, the WGF algorithm allows registration to be performed using only one or two such markers. One important finding is that the use of a single very accurate point (a bone-implanted marker) allows very accurate surface-based registration to be achieved using very few surface points. Finally, the WGF algorithm, which not only allows the combination of multiple types of geometrical information but also handles point-based and surface-based registration as degenerate cases, could form the foundation of a "flexible" surgical navigation system that allows the surgeon to use what he considers the method most appropriate for an individual clinical situation.

Algorithms↗
PubMed1998

Sexual dysfunction associated with the management of prostate cancer.

Improvements in the management of prostate cancer have increased the need to consider patients' quality of life, in particular in relation to sexual function. The causes of sexual dysfunction are varied and derive from both the condition and its management. Health professionals must choose their treatment strategies with great care. Patient expectations must be understood, and patients should be offered counselling, as an understanding of what can reasonably be expected contributes to patients' perception of their quality of life. There are few studies on sexual dysfunction in patients with prostate cancer. A first step would be to develop reliable questionnaires for the assessment of the problem. This article describes and discusses the findings of one such recently developed questionnaire. When baseline measures of sexual function have been established and the extent of sexual dysfunction in patients with prostate cancer is reliably quantified, large multicentre trials can be performed to evaluate the impact of different therapies on sexual function and quality of life. Sexual dysfunction is an area which will be of increasing importance to urologists who manage prostate cancer and one that should not be underestimated.

Aged↗
PubMed1997

Measuring clinical nurse performance: development of the King's Nurse Performance Scale.

The development of the King's Nurse Performance Scale to measure clinical nurse performance is described. Instrument construction was informed by the Slater Nursing Competencies Rating Scale [Wandelt, M. A. and Stewart, D. S. (1975) Slater Nursing Competencies Rating Scale. Appleton-Century Crofts, New York] together with key literature and the use of expert opinion. The instrument was utilised to observe the clinical performance of senior student nurses (n = 99) and data which were at the ordinal level were statistically analysed using a variety of non-parametric tests. Key findings of students' observed nursing practice are presented in a separate paper (While et al., unpublished document). Internal consistency testing of the King's Nurse Performance Scale using Cronbach's alpha coefficient revealed a promising alpha for the total instrument (r = 0.93). The subsection alphas indicated that further refinement may enhance the strength of the instrument as a tool for the measurement of performance in different domains of practice. The possible use of the Scale in the professional development of newly qualified nurses is suggested.

Clinical Competence↗
PubMed1997

Transurethral needle ablation of the prostate for the treatment of benign prostatic hyperplasia: a collaborative multicentre study.

OBJECTIVE: To assess the efficacy and safety of transurethral needle ablation of the prostate (TUNA) for patients with symptomatic benign prostatic hyperplasia (BPH) in a multicentre trial. PATIENTS AND METHODS: Seventy-six patients were recruited from five centres; all were treated with the TUNA system consisting of a powered radiofrequency generator and a TUNA catheter. The patients were evaluated prospectively using the international prostate symptom score (IPSS), uroflowmetry, quality-of-life score, and other variables, and followed for a mean of 12 months after treatment. RESULTS: Sixty-eight patients were available for follow-up: TUNA produced significant improvements in the IPSS (median 22 before, to 7.5 after treatment). urinary flow rate (mean 8.7 before, to 11.6 mL/s after treatment) and quality-of-life score (median 5 before, to 2 after treatment) at 12 months. CONCLUSIONS: If these early promising results are maintained. In the medium to long term, TUNA therapy will be a useful low-morbidity alternative for patients with symptomatic BPH.

Aged↗
PubMed1997

High-intensity focused ultrasound in the treatment of benign prostatic hyperplasia.

OBJECTIVE: To assess the role of high-intensity focused ultrasound (HIFU) in the treatment of symptomatic benign prostatic hyperplasia (BPH). PATIENTS AND METHODS: Thirteen patients (mean age 65 years, range 58-74) were treated with HIFU as part of a phase-2 clinical trial and evaluated prospectively using the International Prostate Symptom Score, uroflowmetry, and transrectal and transabdominal ultrasonography to determine prostate size and post-void residual urine volume, respectively. The results and the patients' satisfaction were assessed at regular intervals for 2 years. RESULTS: The new procedure was learned quickly and was easy to perform. Symptom scores decreased from a mean of 23 before treatment to 5 after 12 months and 7 after 2 years. There was an initial improvement in flow rates but they then declined. The size of the prostate and the post-void residual volume were both decreased after treatment. CONCLUSIONS: The treatment is safe, easy to implement and was effective in substantially reducing symptom scores in these few patients. However, we would not encourage its use as an alternative to other well established treatment modalities until it has been assessed fully in a randomized trial.

Aged↗
PubMed1997

Determination of testicular function after torsion by DNA flow cytometry of serial fine-needle aspirates.

OBJECTIVE: To determine the efficacy of DNA flow cytometric analysis of testicular percutaneous fine-needle aspirates in the assessment and follow-up of testicular function after torsion, and to determine the relationship between the duration of torsion and testicular injury. MATERIALS AND METHODS: Three groups of 15 adult rats underwent a 720 degrees torsion, with fixation of the mesorchial ligament, for 1, 3 or 5 h. Bilateral aspirations, performed 7, 21 and 35 days after torsion were examined by flow cytometry. Testes were harvested and evaluated histologically using Johnsen's scoring. RESULTS: Irreversible testicular injury occurred in all three groups of rats, with loss of function after 1 h and loss of viability after 3 and 5 h. The results from flow cytometry suggested significant contralateral testicular injury (P < 0.025) but this was not supported by the histological evaluation. There was a strong correlation between the testicular function assessed by flow cytometry and by Johnsen's scoring of histological specimens (r2 = 0.95). CONCLUSION: The assessment of testicular aspirates by flow cytometry allows testicular function to be followed after torsion in rats, and potentially in humans. Using DNA flow cytometry, the temporal course of the twisted testis in the adult rat was determined; contralateral testicular injury following the reversal of torsion could not be excluded.

Animals↗
PubMed1997

Registration of head volume images using implantable fiducial markers.

In this paper, we describe an extrinsic-point-based, interactive image-guided neurosurgical system designed at Vanderbilt University, Nashville, TN, as part of a collaborative effort among the Departments of Neurological Surgery, Computer Science, and Biomedical Engineering. Multimodal image-to-image (II) and image-to-physical (IP) registration is accomplished using implantable markers. Physical space tracking is accomplished with optical triangulation. We investigate the theoretical accuracy of point-based registration using numerical simulations, the experimental accuracy of our system using data obtained with a phantom, and the clinical accuracy of our system using data acquired in a prospective clinical trial by six neurosurgeons at four medical centers from 158 patients undergoing craniotomies to resect cerebral lesions. We can determine the position of our markers with an error of approximately 0.4 mm in X-ray computed tomography (CT) and magnetic resonance (MR) images and 0.3 mm in physical space. The theoretical registration error using four such markers distributed around the head in a configuration that is clinically practical is approximately 0.5-0.6 mm. The mean CT-physical registration error for the phantom experiments is 0.5 mm and for the clinical data obtained with rigid head fixation during scanning is 0.7 mm. The mean CT-MR registration error for the clinical data obtained without rigid head fixation during scanning is 1.4 mm, which is the highest mean error that we observed. These theoretical and experimental findings indicate that this system is an accurate navigational aid that can provide real-time feedback to the surgeon about anatomical structures encountered in the surgical field.

Brain Diseases↗
PubMed1996

Methods of renal blood flow measurement.

Variations in regional renal blood flow have been implicated in a variety of disease states. Many techniques have been developed in an attempt to accurately assess these changes. The microsphere technique is the most widely used method at the present time. This technique allows focal measurements to be performed, but there is a conflict between the resolution of the method and the number of microspheres necessary in each sample. New imaging techniques such as tomography and autoradiography enable visual assessment of renal blood flow. Though there is no ideal method, these techniques have opened up new possibilities in the quantification of regional renal blood flow.

Autoradiography↗
PubMed1996

Operationalisation of an observation instrument to explore nurse performance.

This paper explores the operationalization of an observation instrument to explore actual situated behaviour in the clinical setting. Challenges encountered during this process and strategies employed to address these difficulties are discussed. This work formed part of a comparative study of outcomes of pre-registration nurse education programmes commissioned by the English National Board for Nursing, Health Visiting and Midwifery.

Clinical Competence↗
PubMed1996

Key influences on the professional socialisation and practice of students undertaking different pre-registration nurse education programmes in the United Kingdom.

A principal aim of pre-registration nurse education programmes is the process of effective socialisation of students into the professional role. Key influences on the professional socialisation and practice of students undertaking such programmes were explored using a semi-structured interview approach (N = 99). This work formed part of a major comparative study of outcomes of pre-registration nurse education programmes in the United Kingdom. Analysis revealed differences between the programmes regarding positive influences of the respective courses; therapeutic influences of the practice environment; modelling performance on exemplars of high quality practice; and the identification of teachers within the educational setting and nurses in practice as key persons. This study has confirmed that the positive influence of the education programmes and the practice environment as well as high quality role models from both education and practice establishments are critical to the professional socialisation of student nurses.

Curriculum↗