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Frank J Rybicki

Publications and source records attributed to Frank J Rybicki.

At least 19 recordsLinked to original sources
PubMed2007

Reimbursement for chest-pain CT: estimates based on current imaging strategies.

The purpose of this study was to estimate reimbursement for chest pain CT, assuming no cost increase for current emergent chest pain imaging. Using reported imaging test characteristics, prevalence and risk of coronary heart disease, and Medicare reimbursement schedules, 10,000 simulated patients were evaluated with three chest pain imaging algorithms. The main difference among the algorithms was the initial imaging tool: stress echocardiography, single photon emission computed tomography (SPECT) and chest pain CT. Outcome analysis included deaths, intra- and extra-hospital myocardial infraction, number of tests performed, time utilization, and the cost per patient. The chest pain CT algorithm was assessed with its reimbursement as an unknown to determine a maximum reimbursement that would not increase overall healthcare costs. Stress echocardiography costs $856.5 per patient with 8.4 observation hours and 646 (27%) negative catheterizations. When SPECT replaces stress echocardiography, the cost increases to $1,413.7 with average observation of 9.05 hours and 1,060 (36%) negative catheterizations. Chest pain CT minimizes observation (by 8.4 and 9.1 compared to echocardiography and SPECT, respectively); negative catheterizations drop to 266 (12%). Solving for chest pain CT reimbursement as an unkown yields $433.1 and $990.3 when compared to echocardiography and SPECT, respectively. Under the assumption that new technology should not increase overall imaging costs, reimbursement for chest pain CT is compatible with current reimbursement for pulmonary embolism and aortic dissection CTA. Reimbursements must be weighed against the complexity and patient benefits of the examination.

Algorithms↗
PubMed2006

Enhancing the acquisition efficiency of fast magnetic resonance imaging via broadband encoding of signal content.

Current efficient magnetic resonance imaging (MRI) methods such as parallel-imaging and k-t methods encode MR signals using a set of effective encoding functions other than the Fourier basis. This work revisits the proposition of directly manipulating the set of effective encoding functions at the radiofrequency excitation step in order to increase MRI efficiency. This approach, often termed "broadband encoding," enables the application of algebraic matrix factorization technologies to extract efficiency by representing and encoding MR signal content in a compacted form. Broadband imaging equivalents of fast multiecho, parallel and k-t MRI are developed and analyzed. The potential of these techniques to increase the time efficiency of data acquisition is experimentally verified on a commercial MRI scanner using simple spin-echo imaging. A three-dimensional gradient-echo dynamic imaging application that demonstrates the potential benefits of this approach compared to the present state of the art for certain applications is also presented.

Fourier Analysis↗
PubMed2006

Periaortic lymphoma as a mimic of posttraumatic intramural hematoma.

Computed tomography (CT) of an 87-year-old man who presented to the emergency department with chest pain after a motor vehicle collision demonstrated multiple broken ribs and a thoracic periaortic soft tissue mass which was high density on precontrast images and enhanced postcontrast. The scan also demonstrated a mass encircling the left ureter and masses in the axilla and pelvis. The enhancement of the periaortic lesion and the presence of the additional soft tissue masses suggested lymphoma as opposed to intramural hematoma (IMH). The diagnosis of follicular B-cell lymphoma was rapidly confirmed with fluorodeoxyglucose-positron emission tomography/CT and excisional biopsy of the axillary lymph node. While this is an atypical presentation, lymphoma and other extravascular pathology must be considered in the evaluation of a periaortic high attenuation mass seen on CT.

Accidents, Traffic↗
PubMed2006

Biexponential characterization of prostate tissue water diffusion decay curves over an extended b-factor range.

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging examinations at 1.5 T, a single 10-mm-thick axial slice was scanned with a line scan diffusion imaging sequence in which 14 equally spaced b factors from 5 to 3,500 s/mm(2) were sampled along three orthogonal diffusion sensitization directions in 6 min. Due to the combination of long scan time and limited volume coverage associated with the multi-b-factor, multidirectional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed noncancerous regions of interest (ROIs) within the central gland (CG) and peripheral zone (PZ). Histology from prescan biopsy (n=9) and postsurgical resection (n=4) was subsequently employed to help confirm that the ROIs sampled were noncancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia, which is prevalent in this population. The water signal decays with b factor from all ROIs were clearly non-monoexponential and better served with bi- vs. monoexponential fits, as tested using chi(2)-based F test analyses. Fits to biexponential decay functions yielded intersubject fast diffusion component fractions in the order of 0.73+/-0.08 for both CG and PZ ROIs, fast diffusion coefficients of 2.68+/-0.39 and 2.52+/-0.38 microm(2)/ms and slow diffusion coefficients of 0.44+/-0.16 and 0.23+/-0.16 um(2)/ms for CG and PZ ROIs, respectively. The difference between the slow diffusion coefficients within CG and PZ was statistically significant as assessed with a Mann-Whitney nonparametric test (P<.05). We conclude that a monoexponential model for water diffusion decay in prostate tissue is inadequate when a large range of b factors is sampled and that biexponential analyses are better suited for characterizing prostate diffusion decay curves.

Aged↗
PubMed2006

Does the phase of menstrual cycle affect MR-guided focused ultrasound surgery of uterine leiomyomas?

PURPOSE: To determine whether the phase of menstrual cycle at the time of MR-guided focused ultrasound surgery (MRgFUS) treatment for uterine leiomyomas affects treatment outcome. METHODS: We enrolled all patients participating in a prospective phase III clinical trial from our center who completed 6 months of clinical and imaging follow-up. Patients with irregular cycles and those on oral contraceptives were excluded. Data prospectively documenting the date of the last menstrual period (LMP) at the time of treatment, length and duration of cycle, and raw symptom severity score (SSS) from the Uterine Fibroid Symptom and Quality of Life questionnaire, at baseline and 6 months were collected. Proliferative phase patients were determined retrospectively as those who were treated within less than 14 days from LMP; secretory phase patients were classified as those who were treated greater than 14 days from LMP. RESULTS: A total of 58 patients were enrolled. There was no significant difference in the mean SSS at baseline and mean SSS at 6 months between patients treated in the proliferative versus secretory phase of the cycle. No significant difference in the SSS change from baseline to 6 months was seen between the two groups. CONCLUSIONS: Menstrual cycle phase does not influence MRgFUS treatment outcome. Symptomatic improvement occurs with treatment during either phase of the menstrual cycle. Thus, the scheduling of MRgFUS treatment need not be based upon the phase of the menstrual cycle.

Female↗
PubMed2006

Strategies for inner volume 3D fast spin echo magnetic resonance imaging using nonselective refocusing radio frequency pulses.

Fast spin echo (FSE) trains elicited by nonselective "hard" refocusing radio frequency (RF) pulses have been proposed as a means to enable application of FSE methods for high-resolution 3D magnetic resonance imaging (MRI). Hard-pulse FSE (HPFSE) trains offer short (3-4 ms) echo spacings, but are unfortunately limited to imaging the entire sample within the coil sensitivity thus requiring lengthy imaging times, consequently limiting clinical application. In this work we formulate and analyze two general-purpose combinations of 3D HPFSE with inner volume (IV) MR imaging to circumvent this limitation. The first method employs a 2D selective RF excitation followed by the HPFSE train and focuses on required properties of the spatial excitation profile with respect to limiting RF pulse duration in the 5-6 ms range. The second method employs two orthogonally selective 1D RF excitations (a 90x degrees - 180y degrees pair) to generate an echo from magnetization within the volume defined by their intersection. Subsequent echoes are formed via the HPFSE train, placing the focus of the method on (a) avoiding spurious echoes that may arise from transverse magnetization located outside the slab intersection when it is unavoidably affected by the nonselective refocusing pulses and (b) avoiding signal losses due to the necessarily different spacing (in time) of the RF pulse applications. The performance of each method is experimentally measured using Carr-Purcell-Meiboom-Gill (CPMG) multi-echo imaging, enabling examination of the magnetization evolution throughout the echo train. The methods as implemented achieve 95% to 97% outer volume signal suppression, and higher suppression appears to be well within reach, by further refinement of the selective RF excitations. Example images of the human brain and spine are presented with each technique. We conclude that the SNR efficiency of volume imaging in conjunction with the short echo spacing afforded by hard pulse trains enables high-resolution 3D HPFSE MRI of a small field-of-view (FOV) with minimal aliasing artifact.

Algorithms↗
PubMed2006

Uterine leiomyomas: MR imaging-based thermometry and thermal dosimetry during focused ultrasound thermal ablation.

PURPOSE: To retrospectively evaluate magnetic resonance (MR) imaging-based thermometry and thermal dosimetry during focused ultrasound treatments of uterine leiomyomas (ie, fibroids). MATERIALS AND METHODS: All patients gave written informed consent for the focused ultrasound treatments and the current HIPAA-compliant retrospective study, both of which were institutional review board approved. Thermometry performed during the treatments of 64 fibroids in 50 women (mean age, 46.6 years +/- 4.5 [standard deviation]) was used to create thermal dose maps. The areas that reached dose values of 240 and 18 equivalent minutes at 43 degrees C were compared with the nonperfused regions measured on contrast material-enhanced MR images by using the Bland-Altman method. Volume changes in treated fibroids after 6 months were compared with volume changes in nontreated fibroids and with MR-based thermal dose estimates. RESULTS: While the thermal dose estimates were shown to have a clear relationship with resulting nonperfused regions, the nonperfused areas were, on average, larger than the dose estimates (means of 1.9 +/- 0.7 and 1.2 +/- 0.4 times as large for areas that reached 240- and 18-minute threshold dose values, respectively). Good correlation was observed for smaller treatment volumes at the lower dose threshold (mean ratio, 1.0 +/- 0.3), but for larger treatment volumes, the nonperfused region extended to locations within the fibroid that clearly were not heated. Variations in peak temperature increase were as large as a factor of two, both between patients and within individual treatments. On average, the fibroid volume reduction at 6 months increased as the ablated volume estimated by using the thermal dose increased. CONCLUSION: Study results showed good correlation between thermal dose estimates and resulting nonperfused areas for smaller ablated volumes. For larger treatment volumes, nonperfused areas could extend within the fibroid to unheated areas.

Adult↗
PubMed2006

Regional brain development in serial magnetic resonance imaging of low-risk preterm infants.

OBJECTIVE: MRI studies have shown that preterm infants with brain injury have altered brain tissue volumes. Investigation of preterm infants without brain injury offers the opportunity to define the influence of early birth on brain development and provide normative data to assess effects of adverse conditions on the preterm brain. In this study, we investigated serial MRI of low-risk preterm infants with the aim to identify regions of altered brain development. METHODS: Twenty-three preterm infants appropriate for gestational age without magnetic resonance-visible brain injury underwent MRI twice at 32 and at 42 weeks' postmenstrual age. Fifteen term infants were scanned 2 weeks after birth. Brain tissue classification and parcellation were conducted to allow comparison of regional brain tissue volumes. Longitudinal brain growth was assessed from preterm infants' serial scans. RESULTS: At 42 weeks' postmenstrual age, gray matter volumes were not different between preterm and term infants. Myelinated white matter was decreased, as were unmyelinated white matter volumes in the region including the central gyri. The gray matter proportion of the brain parenchyma constituted 30% and 37% at 32 and 42 weeks' postmenstrual age, respectively. CONCLUSIONS: This MRI study of preterm infants appropriate for gestational age and without brain injury establishes the influence of early birth on brain development. No decreased cortical gray matter volumes were found, which is in contrast to findings in preterm infants with brain injury. Moderately decreased white matter volumes suggest an adverse influence of early birth on white matter development. We identified a sharp increase in cortical gray matter volume in preterm infants' serial data, which may correspond to a critical period for cortical development.

Brain↗
PubMed2005

Measures of performance in nonlinear estimation tasks: prediction of estimation performance at low signal-to-noise ratio.

Maximum-likelihood (ML) estimation is an established paradigm for the assessment of imaging system performance in nonlinear quantitation tasks. At high signal-to-noise ratio (SNR), ML estimates are asymptotically Gaussian-distributed, unbiased and efficient, thereby attaining the Cramer-Rao bound (CRB). Therefore, at high SNR the CRB is useful as a predictor of the variance of ML estimates and, consequently, as a basis for measures of estimation performance. At low SNR, however, the achievable parameter variances are often substantially larger than the CRB and the estimates are no longer Gaussian-distributed. These departures imply that inference about the estimates that is based on the CRB and the assumption of a normal distribution will not be valid. We have found previously that for some tasks these effects arise at noise levels considered clinically acceptable. We have derived the mathematical relationship between a new measure, chi2(pdf-ML), and the expected probability density of the ML estimates, and have justified the use of chi2(pdf-ML)-isocontours in parameter space to describe the ML estimates. We validated this approach by simulation experiments using spherical objects imaged with a Gaussian point spread function. The parameters, activity concentration and size, were estimated simultaneously by ML, and variances and covariances calculated over 1000 replications per condition from 3D image volumes and from 2D tomographic projections of the same object. At low SNR, where the CRB is no longer achievable, chi2(pdf-ML)-isocontours provide a robust prediction of the distribution of the ML estimates. At high SNR, the chi2(pdf-ML)-isocontours asymptotically approach the analogous chi2(pdf-F)-contours derived from the Fisher information matrix. The chi2(pdf-ML) model appears to be suitable for characterization of the influence of the noise level and characteristics, the task, and the object on the shape of the probability density of the ML estimates at low SNR. Furthermore, it provides unique insights into the causes of the variability of estimation performance.

Algorithms↗
PubMed2005

Atlantoaxial instability associated with an orthotopic os odontoideum: a multimodality imaging assessment.

Radiography, computed tomography (CT), and magnetic resonance imaging exams of the cervical spine were performed in a 29-year-old man who was ultimately diagnosed with an orthotopic os odontoideum during admission for injuries sustained in a motor vehicle collision. Initial radiography suggested either os odontoideum or an acute fracture of the dens. Further imaging with CT and flexion and extension radiographs confirmed os odontoideum and excluded a dens fracture. Although rare, os odontoideum is an important cervical spine anomaly to consider and to distinguish from an acute fracture of the dens.

Adult↗
PubMed2005

Three dimensional computed tomographic imaging in planning the surgical approach for redo cardiac surgery after coronary revascularization.

OBJECTIVE: Reoperative cardiac surgery after previous coronary artery bypass grafting represents a surgical challenge due to the potential for injury to patent coronary grafts, aorta or right ventricle. Standard preoperative imaging using a coronary angiogram and chest radiograph (CXR) often results in inaccurate assessment of mediastinal anatomy. We aimed to evaluate 3D volume rendered computed tomographic imaging as an adjunct to standard preoperative assessment of patients requiring cardiac surgery in whom coronary artery revascularization had been performed in the past. METHODS: Between January 2003 and January 2004, 33 patients with previous coronary revascularization referred for reoperative cardiac surgery underwent preoperative 3D CT imaging in order to optimize the surgical approach. The mean age in this patient population was 72+/-8 years. The combined evaluation of CXR and conventional angiography offered incomplete insight into pertinent mediastinal topography in 85% of patients (28/33). RESULTS: The correlations for distances of the left internal mammary artery (LIMA) to left anterior descending artery (LAD) graft from the midline and posterior sternum obtained by CT angiography (CTA) and CXR were poor, R=0.56 and 0.49, respectively. The correlation coefficients for distances between the right ventricle and the aorta to the sternum obtained by the same methods were similarly marginal, 0.58 and 0.48, respectively. The correlation coefficients for distances between the LIMA to LAD, circumflex and right coronary artery grafts from the midline obtained by CTA and conventional angiography were 0.54, -0.13 and 0.43, respectively. In seven patients (21%) the surgical strategy was modified based on the location of patent grafts in the mediastinum. The hospital mortality was 17% (5/29). Intraoperative injuries to vital structures were encountered in two patients (7%). No injuries to patent LIMA or the aorta were encountered. CONCLUSIONS: The 3D CT imaging technique is useful in defining the optimal surgical strategy for reoperative cardiac surgery. We found that CTA is superior to CXR and conventional angiography in defining the position of patent grafts and vital structures in relation to the midline and posterior sternum. Preoperative mapping of patent coronary grafts and other vital mediastinal structures reduces the morbidity of the reoperation through modification of surgical approaches.

Aged↗
PubMed2005

Acute appendicitis of the appendiceal stump.

We report a case of a 27-year-old man, status post open appendectomy as an infant, in whom the diagnosis of acute appendicitis of the appendiceal stump was made by computed tomography (CT). A coronal reformatted CT image demonstrated both the inflamed appendix and a normal terminal ileum. Although rare, stump appendicitis may present with signs and symptoms typical of acute appendicitis in patients status post appendectomy and should be considered in the differential diagnosis.

Abdominal Pain↗
PubMed2004

Liposarcoma subtypes: identification with computed tomography and ultrasound-guided percutaneous needle biopsy.

The purpose of the study was to evaluate the feasibility of image-guided percutaneous needle biopsy to enable specific subtype classification of liposarcoma in patients with previously diagnosed disease and compare the yield of fine and large needle techniques for each subtype. We reviewed the medical records and pathology reports of 69 fine (20 g) needle and large (15, 16 g) needle biopsies performed in 44 patients enrolled in a clinical trial evaluating the effect of a novel therapy for advanced liposarcoma in the abdomen and pelvis. Cytopathologists and surgical pathologists identified features that enabled them to classify the tumor into one of four subtypes: well differentiated, myxoid/round cell, pleomorphic and dedifferentiated. The pre-study open surgical biopsy was used as the standard for comparison. The diagnostic yield (proportion of biopsies with correct subtype diagnosis) of percutaneous biopsy for identifying all subtypes of liposarcoma was 81% (64% for fine needles and 73% for large needles alone). There was a significant association between pathologic subtype and the probability of a correct diagnosis (P=0.05). Accurate diagnostic subset classification of liposarcoma by percutaneous biopsy is feasible, although both fine and large needles should be used. Although these data cannot be extrapolated to primary diagnosis of liposarcoma, they are important for screening and subtyping of possible recurrence.

Adult↗
PubMed2004

Non-Fourier-encoded parallel MRI using multiple receiver coils.

This paper describes a general theoretical framework that combines non-Fourier (NF) spatially-encoded MRI with multichannel acquisition parallel MRI. The two spatial-encoding mechanisms are physically and analytically separable, which allows NF encoding to be expressed as complementary to the inherent encoding imposed by RF receiver coil sensitivities. Consequently, the number of NF spatial-encoding steps necessary to fully encode an FOV is reduced. Furthermore, by casting the FOV reduction of parallel imaging techniques as a dimensionality reduction of the k-space that is NF-encoded, one can obtain a speed-up of each digital NF spatial excitation in addition to accelerated imaging. Images acquired at speed-up factors of 2x to 8x with a four-element RF receiver coil array demonstrate the utility of this framework and the efficiency afforded by it.

Calibration↗
PubMed2004

Quantification of clinical consultations in academic emergency radiology.

RATIONALE AND OBJECTIVES: The purpose of this study is to quantify the impact of clinical consultation on the workload of an academic emergency radiology section. MATERIALS AND METHODS: Data from a 7-day audit (24 h/d) of the number and length of clinical consultations was expressed as the mean number of consultations per 24 hours and consultation minutes per 24 hours. Consultations performed on images acquired from outside institutions were noted. The attending radiologist consultation fraction was defined as the attending consultation minutes per 24 hours divided by the number of minutes of attending coverage per 24 hours. Using annualized work relative value units per full-time employee (wRVU/FTE) over the 7 days, the consultation value unit per full-time employee (CVU/FTE) was defined and calculated as the consultation fraction multiplied by the annual wRVU/FTE. RESULTS: For the attending radiologists, the consultation fraction was 0.13 and the CVU/FTE was 1216. Twenty-two percent of the total consultation minutes were spent on studies performed outside our institution. CONCLUSIONS: Clinical consultation represents a significant portion of the workload in academic emergency radiology. The consultation fraction describes the fraction of the radiologist's time spent in consultation, and the CVU/FTE expresses the workload of clinical consultations in terms of wRVU/FTE, the factor used most commonly to determine the academic radiologist's productivity and staffing.

Academic Medical Centers↗
PubMed2004

Spatially selective T2 and T2 * measurement with line-scan echo-planar spectroscopic imaging.

Line-scan echo planar spectroscopic imaging (LSEPSI) is applied to quickly measure the T2 and T2* relaxation time constants in pre-selected 2D or 3D regions. Results from brain imaging studies at 3T suggest that the proposed method may prove valuable for both basic research (e.g., quantifying the changes of T2/T2* values in functional MRI with blood oxygenation level-dependent contrast) and clinical studies (e.g., measuring the T2' shortening due to iron deposition). The proposed spatially selective T2 and T2* mapping technique is especially well suited for studies, where T2/T2* quantification needs to be performed dynamically in a pre-selected 2D or 3D region.

Brain↗