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Biomedical subjects

Michael M Maher

Publications and source records attributed to Michael M Maher.

At least 19 recordsLinked to original sources
PubMed2005

Attenuation of acute and chronic pulmonary emboli.

PURPOSE: To compare retrospectively the attenuation coefficients of acute and chronic pulmonary embolism (PE). MATERIALS AND METHODS: Institutional review board approval was obtained, and informed consent was waived. The study was compliant with requirements of the Health Insurance Portability and Accountability Act. All patients with chronic PE, from July 2001 to January 2004, were identified via a radiology report search system; of the 39 identified, 25 were excluded because the thrombi were too small to measure or were obscured by streak artifacts or because there was no corroborative evidence of chronic PE. Of 27 consecutive patients with acute PE who were also identified, two were excluded because of streak artifacts. The final study group included six women and eight men with chronic PE (mean age, 50 years; range, 26-76 years) and 11 women and 14 men with acute PE (mean age, 61 years; range, 33-83 years) (P = .01 for age). Images were acquired with a four-detector row computed tomographic scanner and 1.25-mm collimation. Two readers made independent attenuation measurements of the largest thrombus in each patient at a workstation. Statistical analysis included calculation of means and standard deviations, the t test, and the Bland-Altman test. RESULTS: Reader 1 found mean attenuation of 90 HU +/- 30 (range, 54-155 HU) for chronic PE and 33 HU +/- 15 (range, 6-63 HU) for acute PE (P < .001). Reader 2 found mean attenuation measurements of 83 HU +/- 32 (range, 32-135 HU) for chronic PE and 33 HU +/- 14 (range, 13-65 HU) for acute PE (P < .001). The mean attenuation for both readers was 33 HU for acute PE (95% confidence interval: 26, 41 HU) and 87 HU for chronic PE (95% confidence interval: 66, 107 HU). The Bland-Altman test demonstrated agreement between readers. CONCLUSION: The mean attenuation measurement in chronic PE is significantly higher than in acute PE.

Acute Disease↗
PubMed2005

Detection of urinary tract stones at low-radiation-dose CT with z-axis automatic tube current modulation: phantom and clinical studies.

PURPOSE: To evaluate depiction of urinary tract calculi at computed tomography (CT) with a z-axis modulation technique at various noise indexes to reduce radiation dose and preserve image quality. MATERIALS AND METHODS: Sixteen radiopaque kidney stones (2.5-19.2 mm in diameter) were embedded in the collecting systems of two bovine kidneys immersed in a water bath. A kidney phantom was made by placing the kidneys in an elliptical Plexiglas phantom (32 x 20 x 20 cm) filled with physiologic saline. The phantom was scanned at 16-detector row CT with a fixed tube current (300 mA) and z-axis modulation at noise indexes of 14, 20, 25, 35, and 50; remaining imaging parameters were held constant. Two abdominal radiologists reviewed images from most to least noisy. Images were evaluated for presence of stones and size, site, and attenuation value of each stone. Readers also graded conspicuity and margins of each stone on a five-point scale. In addition, follow-up studies of 22 patients (mean age, 46 years; range, 26-57 years; male-female ratio, 14:8) with kidney and ureteral stones who underwent CT with z-axis modulation (noise index, 14 and 20) were evaluated in the same manner. Statistical analysis was performed with the Student t test, Wilcoxon signed rank test, and kappa test of interobserver agreement. Institutional review board approval was obtained, and informed consent was not needed. RESULTS: In the phantom study, all 16 stones were identified on images obtained with a fixed tube current and z-axis modulation at noise indexes of 14, 20, and 25 (with a reduction in radiation dose of up to 77% compared with that of fixed tube current scanning). Three stones (<5 mm) were not visualized with z-axis modulation at noise indexes of 35 and 50. No significant difference was shown for conspicuity of kidney stones in 22 patients who underwent CT with z-axis modulation (with a 43%-66% reduction in radiation dose) when compared with results of previous fixed tube current studies (P > .05). CONCLUSION: Kidney stones (< or =2.5 mm) can be adequately depicted with the z-axis modulation technique, with a 56%-77% reduction in radiation dose. In patients with urinary tract stones, the technique results in a 43%-66% reduction in radiation dose at noise indexes of 14 and 20 without compromising stone depiction.

Adult↗
PubMed2005

Do metallic endoprostheses increase radiation dose associated with automatic tube-current modulation in abdominal-pelvic MDCT? A phantom and patient study.

OBJECTIVE: Our objective was to assess the effect of orthopedic metallic prostheses on radiation dose associated with MDCT using z-axis automatic tube-current modulation and a fixed tube current in a phantom and patient study. CONCLUSION: Z-modulation is associated with a 34.1% increase in the mean tube current-time product and no change in the extent of streak artifacts in patients with a metallic prosthesis, compared with patients without a prosthesis. However, compared with the fixed-tube-current technique, z-modulation is associated with a 28.9% decrease in the mean tube current-time product.

Adult↗
PubMed2004

Application of recently developed computer algorithm for automatic classification of unstructured radiology reports: validation study.

PURPOSE: To validate the accuracy of Lexicon Mediated Entropy Reduction (LEXIMER), a new information theory-based computer algorithm developed by the authors for independent analysis and classification of unstructured radiology reports based on the presence of clinically important findings (F(T), where (T) represents "true") and recommendations for subsequent action (R(T)). MATERIALS AND METHODS: The study was approved by the Human Research Committee of the institutional review board. Consecutive de-identified radiology reports (n = 1059) comprising results of barium studies (n = 99), computed tomography (n = 107), mammography (n = 90), magnetic resonance imaging (n = 108), nuclear medicine (n = 99), positron emission tomography (n = 106), radiography (n = 212), ultrasonography (n = 131), and vascular procedures (n = 107) were independently analyzed by two radiologists and then with LEXIMER to categorize the reports into F(T) and F(T)0 (containing or not containing clinically important findings) categories and R(T) and R(T)0 (containing or not containing recommendations for subsequent action) categories. Accuracy, sensitivity, specificity, and positive and negative predictive values of LEXIMER for placing reports into F(T) and F(T)0 and R(T) and R(T)0 categories were assessed by using appropriate statistical tests. RESULTS: There was strong interobserver concordance between the two radiologists for placing radiology reports into F(T) and R(T) categories (kappa = 0.9, P < .01). For the LEXIMER program, accuracy, sensitivity, specificity, and positive and negative predictive values, respectively, were 97.5% (95% confidence interval [CI]: 96.6%, 98.5%), 98.9% (95% CI: 97.9%, 99.6%), 94.9% (95% CI: 93.1%, 96.0%), 97.5% (95% CI: 96.6%, 98.0%), and 97.7% (95% CI: 95.8%, 98.8%) for placing radiology reports into F(T) and F(T)0 categories and 99.6% (95% CI: 99.2%, 99.9%), 98.2% (95% CI: 95.0%, 99.6%), 99.9% (95% CI: 99.4%, 99.99%), 99.4% (95% CI: 96.3%, 99.9%), and 99.7% (95% CI: 98.9%, 99.9%) for placing reports into R(T) and R(T)0 categories. CONCLUSION: LEXIMER is an accurate automated engine for evaluating the percentage positivity of clinically important findings and rates of recommendation for subsequent action in unstructured radiology reports.

Algorithms↗
PubMed2004

Techniques and applications of automatic tube current modulation for CT.

Introduction of slip-ring technology with subsequent development of single- and multi-detector row helical computed tomographic (CT) scanners have expanded the applications of CT, leading to a substantial increase in the number of CT examinations being performed. Owing to concerns about the resultant increase in associated radiation dose, many technical innovations have been introduced. One such innovation is automatic tube current modulation. The purpose of automatic tube current modulation is to maintain constant image quality regardless of patient attenuation characteristics, thus allowing radiation dose to patients to be reduced. This review discusses the principles, clinical use, and limitations of different automatic tube current modulation techniques.

Equipment Design↗
PubMed2004

Autoimmune pancreatitis: imaging features.

PURPOSE: To retrospectively determine imaging findings in patients with autoimmune pancreatitis. MATERIALS AND METHODS: Twenty-nine patients (25 male and four female; mean age, 56 years; range, 15-82 years) with histopathologic diagnosis of autoimmune pancreatitis were examined. Data were reviewed by two radiologists in consensus. Imaging findings for review included those from helical computed tomography (CT), 25 patients; magnetic resonance (MR) imaging with MR cholangiopancreatography (MRCP), four patients; endoscopic ultrasonography (US), 21 patients; endoscopic retrograde cholangiopancreatography (ERCP), 19 patients; and percutaneous transhepatic cholangiography, one patient. Images were analyzed for appearances of pancreas, biliary and pancreatic ducts, and other findings, such as peripancreatic inflammation, encasement of vessels, mass effect, pancreatic calcification, peripancreatic nodes, and peripancreatic fluid collection. Follow-up images were available in nine patients. Serologic markers such as serum immunoglobulin G (IgG) and antinuclear antibody levels were available in 12 patients. RESULTS: CT showed diffuse (n = 14) and focal (n = 7) enlargement of pancreas. Seven patients had minimal peripancreatic stranding, with lack of vascular encasement, calcification, or peripancreatic fluid collection. Nine patients had enlarged peripancreatic lymph nodes. MR imaging showed focal (n = 2) and diffuse (n = 2) enlargement with rimlike enhancement in one. MRCP revealed pancreatic duct strictures in two and sclerosing cholangitis-like appearance in one. Endoscopic US showed diffuse enlargement of pancreas with altered echotexture in 13 patients and focal mass in the head in six. ERCP showed stricture of distal common bile duct in 12 patients, irregular narrowing of intrahepatic ducts in six, diffuse irregular narrowing of pancreatic duct in nine, and focal stricture of proximal pancreatic duct in six. Serologic markers showed increased IgG and antinuclear antibody levels in seven of 12 patients. At follow-up, CT abnormalities and common bile duct strictures resolved after steroid therapy in three patients. CONCLUSION: Features that suggest autoimmune pancreatitis include focal or diffuse pancreatic enlargement, with minimal peripancreatic inflammation and absence of vascular encasement or calcification at CT and endoscopic US, and diffuse irregular narrowing of main pancreatic duct, with associated multiple biliary strictures at ERCP.

Adolescent↗
PubMed2004

Acute pancreatitis: the role of imaging and interventional radiology.

Acute pancreatitis can manifest as a benign condition with minimal abdominal pain and hyperamylasemia or can have a fulminant course, which can be life-threatening usually due to the development of infected pancreatic necrosis, and multisystem organ failure. Fortunately, 70-80% of patients with acute pancreatitis have a benign self-limiting course (figs. 1, 2, 4). The initial 24-48 hours after the initial diagnosis is usually the period that determines the subsequent course, and for many of the 20-30% of patients who subsequently have a fulminant course, this becomes apparent within this time frame. With reference to long-term outcome following acute pancreatitis, most cases recover without long-term sequelae with only a minority of cases progressing to chronic pancreatitis. In the initial management of acute pancreatitis, assessment of metabolic disturbances and systemic organ dysfunction is critical. However, the advent and continued refinement of cross-sectional imaging modalities over the past two decades has led to a prominent role for diagnostic imaging in assessing acute pancreatitis. Furthermore, these cross-sectional imaging modalities have enabled the development of diagnostic and therapeutic interventional techniques in the hands of radiologists. In this article we review the diagnostic features of acute pancreatitis, the clinical staging systems, complications and the role of imaging. The role of interventional radiology techniques in the management of acute pancreatitis will be discussed as well as potential complications associated with these treatments.

Acute Disease↗
PubMed2004

Strategies for CT radiation dose optimization.

Recent technologic advances have markedly enhanced the clinical applications of computed tomography (CT). While the benefits of CT exceed the harmful effects of radiation exposure in patients, increasing radiation doses to the population have raised a compelling case for reduction of radiation exposure from CT. Strategies for radiation dose reduction are difficult to devise, however, because of a lack of guidelines regarding CT examination and scanning techniques. Various methods and strategies based on individual patient attributes and CT technology have been explored for dose optimization. It is the purpose of this review article to outline basic principles of CT radiation exposure and emphasize the need for CT radiation dose optimization based on modification of scanning parameters and application of recent technologic innovations.

Adult↗
PubMed2004

Application of rational practice and technical advances for optimizing radiation dose for chest CT.

Though clinical benefits of CT exceed the adverse effects of radiation, the increasing use of CT has raised a compelling case for reducing radiation exposure. This controversy has been compounded by the sheer magnitude of CT examinations being performed annually, alleged overuse, and inappropriate selection of optimum scanning parameters, all of which expose the patient population to increased radiation exposure. Recommended clinical strategies for radiation dose optimization include optimization of scanning parameters and creating awareness and adopting guidelines for legitimate indications for CT scanning to avoid overuse and hence, the associated over-exposure. Whereas technological advances have increased the applications of the modality, it is also assisting in development of promising techniques to reduce associated radiation exposure, while maintaining "optimum image quality" needed to make a confident diagnosis. The present pictorial essay describes the fundamentals of CT radiation exposure and need for CT radiation dose reduction on the basis of documented scanning practices and technological advances.

Humans↗
PubMed2004

Haemolysis, elevated liver enzymes and low platelets syndrome: ultrasound and magnetic resonance imaging findings in the liver.

We describe the imaging findings of the HELLP (haemolysis, elevated liver enzymes and low platelets) syndrome in a gravid 36-year-old-woman who presented at 19.5 weeks gestation with severe right upper quadrant pain. Ultrasound findings suggested a focal hyperechoic liver lesion suggesting pregnancy-related hepatopathy prior to development of biochemical signs of HELLP syndrome. Within 3 days, the patient developed characteristic clinical and laboratory evidence of the HELLP syndrome. MR imaging at this time demonstrated localized hepatic ischaemia, further strengthening the diagnosis of HELLP syndrome.

Adult↗
PubMed2004

Radiation from "extra" images acquired with abdominal and/or pelvic CT: effect of automatic tube current modulation.

PURPOSE: To retrospectively determine the number and usefulness of images acquired beyond the intended anatomic area of interest with abdominal and/or pelvic computed tomography (CT) and to assess the effect of automatic tube current modulation (ATCM) on associated radiation. MATERIALS AND METHODS: Superior and inferior levels at routine abdominal and/or pelvic CT were defined as the dome of the diaphragm and the inferior margin of the pubic symphysis, respectively. Records of 106 consecutive examinations (male-to-female ratio, 45:61; age range, 21-86 years) performed from June 1 to June 30, 2003, were reviewed to determine the number of "extra" images. Sixty-two abdominal and/or pelvic CT examinations performed concurrently with chest or thigh CT or for trauma were not included in the 106. Abdominal and/or pelvic CT was performed with either ATCM (n = 44) or manual selection of tube current (n = 62). CT parameters recorded for each extra image included tube current, peak kilovoltage, and gantry rotation time. Mean and median tube current-time products were calculated for extra images. Extra images were analyzed for pathologic findings. Statistical analysis was performed with the Student t test. RESULTS: Extra images were acquired above the dome of the diaphragm in 103 (97%) of 106 examinations and below the pubic symphysis in 100 (94%) of 106. A total of 1,280 extra images were acquired in 106 examinations (mean, 12 images per examination). Nineteen additional findings were observed on extra images. With ATCM, mean tube current-time product was 74.5 and 120.6 mAs for extra images acquired above the diaphragm and below the pubic symphysis, respectively; with manual selection, mean tube current-time products were 167.5 and 168.3 mAs (P <.05). CONCLUSION: Most extra images acquired at abdominal and/or pelvic CT contributed no additional information. With ATCM, the radiation dose was reduced by a mean of 56% (median, 72%) for extra images above the diaphragm and 29% (median, 36%) for images below the pubic symphysis, compared with dose levels with manual selection.

Adult↗
PubMed2004

Comparison of Z-axis automatic tube current modulation technique with fixed tube current CT scanning of abdomen and pelvis.

PURPOSE: To compare image quality, diagnostic acceptability, and radiation exposure associated with 16-section multi-detector row computed tomographic (CT) examinations of abdomen and pelvis performed with z-axis modulation technique of automatic tube current modulation and with manual selection of fixed tube current. MATERIALS AND METHODS: Sixty-two consecutive subjects (mean age, 60 years; age range, 19-84 years; male-to-female ratio, 35:27) underwent follow-up CT of abdomen and pelvis with use of a 16-section multi-detector row scanner and z-axis modulation technique (10.5-12.0-HU noise index, 10-380 mA). Scanning parameters included 140 kVp, 0.5-1.0-second gantry rotation time, 0.938:1 beam pitch, and 5-mm reconstructed section thickness. For each subject, images obtained with z-axis modulation were compared with previous images obtained with fixed tube current (200-300 mA) and with other parameters identical. Images were compared for noise and diagnostic acceptability by two subspecialty radiologists using a five-point scale (1, unacceptable; 3, acceptable; 5, excellent) at five levels: upper liver at diaphragm, porta hepatis, right kidney hilum, iliac crest, and upper margin of acetabulum. Tube current and gantry rotation time used for acquisitions at these levels were recorded. Data were analyzed with parametric and nonparametric statistical tests. RESULTS: Although no significant differences were found (P =.34), images acquired with z-axis modulation at the levels of the upper liver (diaphragm) and acetabulum had a higher noise and lower diagnostic quality, compared with images acquired with fixed tube current. Compared with fixed tube current, z-axis modulation resulted in tube current-time product reduction in 54 (87%) of 62 examinations (mean reduction, 71.2 mAs) and increase in eight (13%) (mean increase, 17.0 mAs). CONCLUSION: Compared with manually selected fixed tube current, z-axis automatic tube current modulation resulted in reduced tube current-time product and similar image noise and diagnostic acceptability at CT of abdomen and pelvis.

Abdominal Neoplasms↗
PubMed2004

Detection and characterization of lesions on low-radiation-dose abdominal CT images postprocessed with noise reduction filters.

PURPOSE: To assess the effect of noise reduction filters on detection and characterization of lesions on low-radiation-dose abdominal computed tomographic (CT) images. MATERIALS AND METHODS: Low-dose CT images of abdominal lesions in 19 consecutive patients (11 women, eight men; age range, 32-78 years) were obtained at reduced tube currents (120-144 mAs). These baseline low-dose CT images were postprocessed with six noise reduction filters; the resulting postprocessed images were then randomly assorted with baseline images. Three radiologists performed independent evaluation of randomized images for presence, number, margins, attenuation, conspicuity, calcification, and enhancement of lesions, as well as image noise. Side-by-side comparison of baseline images with postprocessed images was performed by using a five-point scale for assessing lesion conspicuity and margins, image noise, beam hardening, and diagnostic acceptability. Quantitative noise and contrast-to-noise ratio were obtained for all liver lesions. Statistical analysis was performed by using the Wilcoxon signed rank test, Student t test, and kappa test of agreement. RESULTS: Significant reduction of noise was observed in images postprocessed with filter F compared with the noise in baseline nonfiltered images (P =.004). Although the number of lesions seen on baseline images and that seen on postprocessed images were identical, lesions were less conspicuous on postprocessed images than on baseline images. A decrease in quantitative image noise and contrast-to-noise ratio for liver lesions was noted with all noise reduction filters. There was good interobserver agreement (kappa = 0.7). CONCLUSION: Although the use of currently available noise reduction filters improves image noise and ameliorates beam-hardening artifacts at low-dose CT, such filters are limited by a compromise in lesion conspicuity and appearance in comparison with lesion conspicuity and appearance on baseline low-dose CT images.

Adult↗
PubMed2004

Sixteen-detector row CT of abdomen and pelvis: study for optimization of Z-axis modulation technique performed in 153 patients.

PURPOSE: To retrospectively determine the optimal noise indexes required to obtain diagnostically acceptable computed tomographic (CT) images of the abdomen and pelvis with z-axis modulation. MATERIALS AND METHODS: Ninety-five patients underwent 16-section multi-detector row CT of the abdomen and pelvis with z-axis modulation at noise indexes of 10.5, 11.0, 11.5, and 12.0 HU with 10-380 mA. Subsequently, 58 patients were scanned at noise indexes of 12.5 and 15.0 HU with 75-380 mA. The weights of all subjects were recorded, and transverse and anteroposterior diameters were measured. The CT images were evaluated for abnormalities and graded for image quality in terms of noise and diagnostic acceptability by using a five-point scale. Objective noise in the liver parenchyma was measured, and the tube current was recorded at each section in all 153 patients. Statistical analyses were performed to determine the appropriate noise index and to assess the effect of patient weight and abdominal diameters on image noise and diagnostic acceptability at different noise indexes. Tube current-time products (in milliampere seconds) at various noise indexes were compared with those at CT previously performed without z-axis modulation. RESULTS: No significant difference in subjective image noise or diagnostic acceptability was found at noise indexes of 10.5-15.0 HU (P =.14), and objective noise was significantly inferior only at a noise index of 15.0 HU (P =.009). Compared with CT scanning at a 10.5-HU noise index, CT scanning at 12.5- and 15.0-HU noise indexes yielded, respectively, 10.0% and 41.3% reductions in radiation exposure. Patient weight and abdominal diameters affected subjective image quality. CONCLUSION: Use of a 15.0-HU noise index at 75-380 mA results in acceptable subjective image noise and diagnostic acceptability but significantly greater objective image noise at routine abdominal-pelvic CT. For greater image quality demands, a noise index of 12.5 HU results in acceptable image quality and a 19.6% reduction in radiation exposure.

Abdomen↗
PubMed2004

Pheochromocytoma: an imaging chameleon.

Pheochromocytomas are rare catecholamine-secreting tumors with many clinical and imaging manifestations. They may produce overwhelming cardiovascular crises if the diagnosis is not made or if appropriate treatment is delayed. It is thus important to recognize both their characteristic and atypical imaging appearances. Pheochromocytomas are encountered, sometimes unexpectedly, across a range of imaging modalities. They are characteristically solid, hypervascular masses with high signal intensity on T2-weighted magnetic resonance (MR) images. A wide spectrum of imaging appearances is seen, however, and pheochromocytomas may mimic other adrenal lesions, both benign and malignant. They may be dark on T2-weighted MR images, in contrast to their more classic bright T2-weighted appearance. Other atypical features include fatty, hemorrhagic, cystic, and calcific changes. Pheochromocytomas may contain sufficient fat to be mistaken for an adenoma at computed tomography (CT) or MR imaging. They may also demonstrate rapid contrast material washout and be mistaken for an adenoma owing to their deenhancement profile; however, their washout pattern can be inconsistent. The appearance of pheochromocytomas at radionuclide imaging is also unpredictable. These characteristics at CT, MR imaging, and scintigraphy pose diagnostic challenges, since they allow pheochromocytomas to mimic many other adrenal masses. Pheochromocytoma is an important, often clinically occult neoplasm with devastating consequences if overlooked. Radiologists must be aware of the various forms that pheochromocytomas can assume at imaging.

Adrenal Gland Neoplasms↗
PubMed2004

Portable abdominal CT: analysis of quality and clinical impact in more than 100 consecutive cases.

OBJECTIVE: Our aim was to determine portable abdominal CT image quality and clinical content in a consecutive series of scans obtained in ICUs at a single center. MATERIALS AND METHODS: All helical portable abdominal CT scans obtained between June 1999 and December 2000 were reviewed by two observers. Image quality was assessed for feature detection and overall quality compared with the patients' contemporaneous stationary CT scans. Hospital records were used to determine patient demographics, scanning indications, and clinical impact and to verify portable CT findings when possible. RESULTS: One hundred twenty-two helical portable CT scans (47 contrast-enhanced) and 41 contemporaneous stationary CT scans in 107 patients were included. IV contrast material improved portable CT scan quality, but quality scores for portable CT scans were consistently lower than those for stationary CT scans, both with and without contrast material. Thirty-three conditions suspected before scanning were supported by findings on portable CT scans, which detected evidence of infection in 18 and hemorrhage in 16 cases and motivated seven laparotomies and six percutaneous drainage procedures. Thirty-three portable CT scans (27%) contributed to a change in patient treatment. Results of surgery or autopsy confirmed portable CT findings in 12 of 17 cases. CONCLUSION: Although image quality is inferior to conventional stationary CT, portable abdominal CT provides important diagnostic information without requiring patient transport outside the ICU. Radiologists should avoid overconfident interpretation of portable CT scans.

Adolescent↗