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Michael M Maher

Publications and source records attributed to Michael M Maher.

At least 19 recordsLinked to original sources
PubMed2005

Distinguishing benign from malignant adrenal masses: multi-detector row CT protocol with 10-minute delay.

PURPOSE: To retrospectively evaluate the accuracy of precontrast attenuation, relative percentage washout (RPW), and absolute percentage washout (APW) in distinguishing benign from malignant adrenal masses at multi-detector row computed tomography (CT). MATERIALS AND METHODS: This HIPAA-compliant retrospective study had institutional review board approval; the need for informed consent was waived. One hundred twenty-two adrenal masses were evaluated in 99 patients (51 men, 48 women; age range, 37-86 years) who had undergone CT performed according to the study protocol and who either were given a pathologic diagnosis or underwent follow-up imaging. Unenhanced images were obtained before administration of 120 mL of an intravenous contrast agent with a 75-second scan delay. Delayed images were obtained after 10 minutes. RPW and APW were computed. Receiver operating characteristic (ROC) analysis was performed to compare mean attenuation and both RPW and APW. Analysis was first performed with the exclusion of pheochromocytomas, myelolipomas, and cysts. Precontrast attenuation criteria specific for benignity or malignancy were determined, and ROC analysis of results for the entire nonpheochromocytoma group was then performed. RESULTS: By using an RPW of 37.5% and excluding cysts and myelolipomas, all malignant lesions were detected with a sensitivity of 100% (17 of 17 lesions) and a specificity of 95% (90 of 95 lesions). Area under the binomial ROC curve (A(z)) values were 0.912, 0.985, and 0.892 for precontrast attenuation, RPW, and APW, respectively. Precontrast attenuation of less than 0 or more than 43 HU indicated benign and malignant entities, respectively. Incorporation of these criteria into the APW analysis yielded a sensitivity of 100% (17 of 17 lesions) and a specificity of 98% (93 of 95 lesions) for a threshold washout value of 52.0%. This attenuation-corrected APW generated the greatest A(z) value (ie, 0.988). Combining all the information available from the protocol yielded a sensitivity of 100% (17 of 17 lesions) and a specificity of 98% (98 of 100 lesions) for differentiating benign from malignant masses. CONCLUSION: Precontrast attenuation of less than 0 HU supercedes the washout profile in the evaluation of an individual adrenal mass. Noncalcified, nonhemorrhagic adrenal lesions with precontrast attenuation of more than 43 HU should be considered suspicious for malignancy.

Adrenal Gland Diseases↗
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

Imaging of thymoma.

Thymomas are the most common mediastinal tumors, usually diagnosed initially by CT. CT scanning can aid in characterization of thymoma and can successfully distinguish thymomas from other benign mediastinal tumors and from lymphoma. However, many of the primary mediastinal masses demonstrate overlap between imaging features and frequently resection is advisable for definitive characterization.

Diagnostic Imaging↗
PubMed2005

Chest CT performed with z-axis modulation: scanning protocol and radiation dose.

Institutional review board approval of the study protocol and waiver of informed consent were obtained. This study was compliant with the Health Insurance Portability and Accountability Act. The purpose of this study was to retrospectively assess the scanning protocol and radiation dose associated with z-axis automatic tube current modulation in multi-detector row CT scanning of the chest. Fifty-three patients (mean age, 54 years; age range, 26-77 years; 25 men, 28 women) underwent 16-detector row chest CT with z-axis modulation and noise indexes of 10.0, 12.5, and 15.0 HU. Two radiologists independently compared images acquired with z-axis modulation and fixed tube current (180-300 mA) techniques for image noise, diagnostic acceptability, and depiction of peripheral bronchovascular markings. Tube current-time product was calculated for each study. There was good interobserver agreement between the two readers (kappa = 0.72). Compared with the fixed tube current technique, z-axis modulation provides acceptable image noise for chest CT, with an 18% and 26% reduction in tube current-time product at 10.0- and 12.5-HU noise indexes, respectively.

Adult↗
PubMed2005

CT images of abdomen and pelvis: effect of nonlinear three-dimensional optimized reconstruction algorithm on image quality and lesion characteristics.

The purpose of this study was to retrospectively assess the effect of a postprocessing nonlinear three-dimensional optimized reconstruction algorithm on image quality and lesion characteristics in abdominal and pelvic computed tomographic (CT) images. Institutional review board approved the HIPAA-compliant study protocol; informed consent was waived. Abdominal and pelvic CT images (40 patients; male-female ratio, 20:20; age range, 28-86 years) at 5-mm (n = 20) and 2-mm (n = 20) section thicknesses were postprocessed with the algorithm at three noise reduction levels. Image noise at the level of porta hepatis and acetabulum was evaluated with a five-point scale (1, no or minimal noise; 5, unacceptable noise), and presence and number of lesions and conspicuity were assessed. Statistical analysis was performed (Wilcoxon signed rank test, analysis of variance). Significant noise reduction was noted at all three levels with the algorithm (P < .05). Reduction in image contrast was noted with only one noise reduction level (P < .0001). The algorithm improves image noise without affecting lesion conspicuity and detection on low-dose abdominal and pelvic CT images.

Adult↗
PubMed2005

Scanning beyond anatomic limits of the thorax in chest CT: findings, radiation dose, and automatic tube current modulation.

OBJECTIVE: Our objective was to determine additional radiation dose associated with scanning beyond the anatomic limits of the thorax in chest CT protocol and to assess the effect of z-axis modulation on the additional radiation dose associated with the scanning protocol. MATERIALS AND METHODS: "Extra" images for routine chest CT were defined as those above lung apices (supraapical) and those caudal to the lowermost portion of lung parenchyma (infrapulmonary), including images obtained beyond the adrenal glands (infraadrenal). One hundred and forty-eight consecutive chest CT examinations (70 men, 78 women; age range, 15-90 years) performed September 13-25, 2003, were reviewed to determine the number of supraapical, infrapulmonary, and infraadrenal extra images. All examinations were performed using z-axis modulation (n = 70) or fixed tube current (n = 78). The CT dose index volume and dose-length product (DLP) values for the extra images were calculated. Two radiologists reviewed these extra images for pathologic findings. Student's t test was used to perform the statistical analysis. RESULTS: One hundred forty-four (97%) examinations had supraapical extra images and 145 (98%) had infrapulmonary extra images. A total of 31 additional findings were observed in extra images. Most clinically important findings were identified in patients with a history of malignancy. With z-axis modulation, the mean DLP for supraapical and infrapulmonary extra images was 39.98 mGy x cm and 132.59 mGy x cm, respectively. With fixed tube current, the mean DLP for supraapical and infrapulmonary extra images was 30.31 mGy x cm and 95.91 mGy x cm, respectively. CONCLUSION: A substantial number of extra images are acquired during chest CT that do not add clinically important information in patients with nonmalignant indications. The use of z-axis modulation increased radiation dose for the extra images.

Adolescent↗
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↗