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Biomedical subjects

Michael M Maher

Publications and source records attributed to Michael M Maher.

At least 37 records · Page 2Linked to original sources
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↗
PubMed2004

Radiation exposure from chest CT: issues and strategies.

Concerns have been raised over alleged overuse of CT scanning and inappropriate selection of scanning methods, all of which expose patients to unnecessary radiation. Thus, it is important to identify clinical situations in which techniques with lower radiation dose such as plain radiography or no radiation such as MRI and occasionally ultrasonography can be chosen over CT scanning. This article proposes the arguments for radiation dose reduction in CT scanning of the chest and discusses recommended practices and studies that address means of reducing radiation exposure associated with CT scanning of the chest.

Humans↗
PubMed2003

Transgluteal approach for percutaneous drainage of deep pelvic abscesses: 154 cases.

PURPOSE: To assess the effectiveness of a computed tomographic (CT) image-guided transgluteal approach for percutaneous drainage of deep pelvic abscesses as an alternative to surgical drainage. MATERIALS AND METHODS: The medical records of 140 patients who underwent percutaneous CT-guided transgluteal drainage of 154 deep pelvic abscesses were reviewed to determine the origins, location, and size of the abscesses; volume of initial aspirate; organisms identified in fluid culture; duration of catheter drainage; incidence of catheter-related pain and procedure-related complications; and short- and long-term outcomes. The resultant data were analyzed with a Fisher exact test for difference in the incidence of postprocedural catheter-site pain between transpiriformis and infrapiriformis approaches. RESULTS: The origins of the pelvic abscesses included postoperative fluid collection (n = 115), perforating appendicitis (n = 6), diverticulitis (n = 16), tubo-ovarian inflammation (n = 5), Crohn disease (n = 10), and internal bowel fistula due to irradiation (n = 2). The abscesses were 4-12 cm in diameter. The volume of the aspirate was 5-310 mL. Laboratory cultures of the aspirate grew mixed flora, but the organism most frequently isolated was Escherichia coli. Catheters were removed after a mean of 8 days. In 134 (96%) of 140 patients, there was complete resolution of the abscess following transgluteal drainage, without subsequent surgery. In six of 140 (4%) patients, incomplete resolution necessitated subsequent surgery for postoperative fluid collection (n = 3), diverticulitis (n = 2), or perforating appendicitis (n = 1). Complications of transgluteal drainage were rare and included hemorrhage in three (2%) of the 140 patients. There was no procedure-related mortality. A transpiriformis approach was significantly more likely to be associated with postprocedural pain (P <.001) than was an infrapiriformis approach. CONCLUSION: Percutaneous CT-guided transgluteal drainage is a safe and effective alternative to surgery for deep pelvic abscesses. Major complications are rare.

Abscess↗
PubMed2003

Abdominal aortic aneurysms: elective endovascular repair versus conventional surgery--evaluation with evidence-based medicine techniques.

PURPOSE: To use evidence-based techniques to compare elective open surgical repair of abdominal aortic aneurysms with endovascular repair by means of stent placement. MATERIALS AND METHODS: A focused clinical question formed the basis of a literature search. Evidence-based criteria were used to appraise and assign a "level of evidence" to retrieved articles. The following data were determined from the best studies: systemic, local, and/or vascular complications; graft failure rates; blood loss; mortality; length of intensive care and/or hospital stay; mid- and long-term outcomes; cost of endovascular repair versus that of surgery; and eligibility for endovascular repair. Absolute risk reductions and/or increases and numbers needed to treat or harm were calculated. RESULTS: The best current evidence came from 22 studies, which showed that there is slight, if any, difference between mortality rates of endovascular repair and surgery. Hospital and/or intensive care stay is shorter, blood loss less, and systemic complications fewer (numbers needed to treat, two to 12) with endovascular repair. Some authors reported a significant increase in local and/or vascular complications with endovascular repair (numbers needed to harm, two to six). Graft failure is significantly more common with endovascular repair (numbers needed to harm, four), and substantive adjunctive interventions are needed. Endovascular repair is more expensive than surgery. CONCLUSION: Elective endovascular repair has short-term benefits compared with surgery. There is slight, if any, difference in mortality. Endovascular repair costs more than surgery. At follow-up, surgical grafts performed better.

Aortic Aneurysm, Abdominal↗
PubMed2003

Can noise reduction filters improve low-radiation-dose chest CT images? Pilot study.

Effect of noise reduction filters on chest computed tomographic (CT) images acquired with 50% radiation dose reduction was evaluated. Two sets of images were acquired with multi-detector row CT at standard (220-280 mA) and 50% reduced (110-140 mA) tube current at the level of the carina. After postprocessing with six noise reduction filters, images were compared with baseline standard-dose images for noise, sharpness, and contrast in lungs, mediastinum, and chest wall. Quantitative image noise was measured in descending thoracic aorta. Modulation transfer functions were calculated from CT images of 50-microm wire. Noise reduction filters reduced image noise on low-radiation-dose chest CT images, with some compromise in image sharpness and contrast assessed qualitatively, and slightly altered modulation transfer function at higher spatial frequencies.

Aged↗
PubMed2003

Low-dose CT of the abdomen: evaluation of image improvement with use of noise reduction filters pilot study.

A prospective assessment of improvement in image quality at low-radiation-dose computed tomography (CT) of the abdomen by using noise reduction filters was performed. CT images acquired at standard and 50% reduced tube current were processed with six noise reduction filters and evaluated by three radiologists for image noise, sharpness, contrast, and overall image quality in terms of abdominal organ depiction. Quantitative image noise and contrast-to-noise ratio were measured. Baseline low-dose CT images were significantly worse than standard-dose CT images (P <.05). A statistically significant reduction of noise in low-dose images processed with three filters was noted. In conclusion, use of noise reduction filters decreased image noise at low-dose CT.

Aged↗
PubMed2003

Multislice CT: update on radiation and screening.

With ever-expanding applications, increasing availability, and accessibility of CT scanners, concerns have been raised about radiation exposure associated with CT scanning. Global statistics and projections suggest increasing use of CT scanning and its contribution to radiation exposure is a cause for concern. Several strategies based on modulation of scanning parameters and technologic improvisations have been developed in an effort to reduce associated radiation dose. This article discusses the basis for rising concern regarding radiation dose associated with CT scanning. The fundamentals of CT dose estimation are described along with strategies that aim to reduce radiation dose associated with CT scanning based on patient characteristics, study indications, and technological innovations.

Humans↗