Biomedical subjects

Michael A Blake

Publications and source records attributed to Michael A Blake.

33 records · Page 2Linked to original sources

PubMed2003

Soluble CD40 ligand levels indicate lipid accumulation in carotid atheroma: an in vivo study with high-resolution MRI.

OBJECTIVE: The CD40/CD40 ligand pathway mediates inflammatory processes important in atherogenesis and the formation of the intraplaque lipid pool. We tested the hypothesis that plasma levels of soluble CD40 ligand are elevated in patients with evidence of a lipid pool on high-resolution magnetic resonance imaging (MRI) of carotid stenoses. METHODS AND RESULTS: We recruited 49 patients with evidence of carotid atherosclerosis on ultrasonography; 3 patients could not undergo carotid MRI because of claustrophobia. The remaining 46 patients underwent high-resolution MRI of the carotid arteries. Two radiologists blinded to all other data determined the presence or absence of an intraplaque lipid pool based on the loss of signal between the 20-ms echo time (TE20) and the fat-suppressed TE55 fast spin-echo images. Plasma levels of soluble CD40 ligand were determined by ELISA. Baseline levels of soluble CD40 ligand were higher among patients with evidence of intraplaque lipid (n=14) than among those without it (n=32; median, 2.54 ng/mL; interquartile range [IQR], 1.85 to 3.52 vs median, 1.58 ng/mL; IQR, 1.21 to 2.39; P=0.02). In contrast, soluble CD40 ligand levels were not correlated with percent diameter stenosis (r=-0.19; P=0.21). The relative risk for intraplaque lipid associated with soluble CD40 ligand levels above the median was 6.0 (95% confidence interval, 1.15 to 31.23; P=0.03). The magnitude of this predictive effect did not substantially change after adjustment for traditional cardiovascular risk factors (relative risk, 5.12; 95% confidence interval, 0.78 to 33.73; P=0.09). CONCLUSIONS: Plasma levels of soluble CD40 ligand may predict patients with features of high-risk atherosclerotic lesions. These data provide novel insight into the mechanism through which elevated levels of soluble CD40 ligand may reflect cardiovascular risk in humans and illustrate the potential value of interfacing high-resolution MRI with studies of vascular inflammation.

Aged↗

PubMed2003

Low-density pheochromocytoma on CT: a mimicker of adrenal adenoma.

OBJECTIVE: Attenuation values on CT of less than 10 H are considered characteristic of adrenal adenomas. Adrenal pheochromocytomas can infrequently contain fat that could result in low attenuation on CT. The purpose of our study was to determine if pheochromocytomas could be confused with adenomas by virtue of their attenuation values on unenhanced CT. MATERIALS AND METHODS: CT attenuation and size of nine adrenal nodules producing pheochromocytoma syndrome were measured on unenhanced CT in nine patients. For five patients who received IV contrast material, washout profiles were also calculated. RESULTS: Two of the nine patients had adrenal lesions with attenuation values of less than 10 H; one had a pheochromocytoma with an attentuation of 9.0 H, and the other had a medullary hyperplasia with an attenuation of 1.8 H. These two nodules showed evidence of microscopic fat at histologic examination. No macroscopic fat was seen on the CT scans. The remaining seven patients had lesions with attenuation values exceeding 10 H (mean value, 25.6 H; range, 1.8-41 H). Mean diameter of the nine tumors (including the hyperplastic nodule) was 3.2 cm (range, 0.8-6.7 cm; SD, +/- 2.3 cm). The two low-attenuation lesions also mimicked adenomas by displaying more than 60% contrast washout on 10-min-delayed contrast-enhanced scans, unlike the other three pheochromocytomas for which we had washout data. CONCLUSION: On CT, pheochromocytomas may have attenuation values less than 10 H and also may display more than 60% washout of contrast agents on delayed scanning. Adrenal pheochromocytomas should be included with adenomas in the differential diagnosis both for masses with low attenuation on unenhanced CT and for lesions exhibiting a high percentage of contrast washout.

Adenoma↗

PubMed2002

Bone mineral density assessment: comparison of dual-energy X-ray absorptiometry measurements at the calcaneus, spine, and hip.

It is widely accepted that bone mineral density (BMD) measurements obtained by dual-energy X-ray absorptiometry (DXA) at the spine, hip, and calcaneus predict fracture risk. Few published studies to date have examined the relationship between pDXA measurements at the calcaneus to those at the hip and spine. It has been demonstrated that T-score-based criteria cannot be universally applied to all skeletal sites and measurement technologies. Our goal was to define the calcaneal T-score threshold equivalent to low bone mass at the hip or spine. A total of 119 female patients between the ages of 33 and 76 yr of age were recruited at Boston University Medical Center for bone densitometry screening. Bone density measurements were obtained at the calcaneus using the portable Norland Apollo Densitometer (Norland Medical Systems, Fort Atkinson, WI) and at the hip and spine using the Norland Eclipse densitometer. By defining a pDXA T-score < or =-1 as a positive test and DXA scores < or =-1 as the presence of low bone mass, we obtained a specificity of 100% and a sensitivity of 73% (positive predictive value 100% and negative predictive value 80%) in detecting low bone mass at the femoral neck in women over age 65 yr. In women between 40 and 65 yr of age, we obtained a sensitivity of 50% and a specificity of 93% (positive predictive value 93% and negative predictive value 50%) in detecting low bone mass at the femoral neck. In women less than 40 yr of age, we obtained a sensitivity of 13% and a specificity of 100% (positive predictive value 100% and negative predictive value 75%) in detecting low bone mass at the femoral neck. From receiver operating characteristic curves, a calcaneal T-score < or =0.0 detects those with a T-score < or =-1 at the femoral neck and lumbar spine with 100% and 85% sensitivity, respectively. Peripheral DXA of the calcaneus is a sensitive and specific test to diagnose low bone mass in women over 65 yr of age. In women under 65 yr of age, this modality, though not as sensitive, is specific in detecting low bone mass. We conclude that a pDXA calcaneal T-score < or =0 is highly sensitive in predicting osteopenia and osteoporosis at the femoral neck and lumbar spine.

Absorptiometry, Photon↗

PubMed2002

Clinical comparison of standard-dose and 50% reduced-dose abdominal CT: effect on image quality.

OBJECTIVE: We hypothesized that radiation doses for abdominal CT could be reduced by adjusting the dose for a patient's weight and cross-sectional abdominal dimensions, with the resultant scans still being of diagnostic quality. SUBJECTS AND METHODS: Using a multidetector CT scanner, we prospectively studied 39 patients who were 65 years and older who had a known history of cancer. After performing a diagnostic contrast-enhanced CT examination, we obtained four slices each (centered at the top of the right kidney) at a standard radiation dose (240-300 mA) and at a 50% reduced dose (120-150 mA) at a constant kilovoltage of 140. Scans were obtained during a single breath-hold, with a 2.5-mm detector configuration and a slice pitch of 6:1. Reconstructed slice thickness was 5 mm. In a blinded review, two radiologists rated the randomized CT scans for overall image quality and anatomic details of liver, spleen, adrenal glands, kidneys, pancreas, and abdominal wall, using a 5-point scale (1 = unacceptable, 2 = substandard, 3 = acceptable, 4 = above average, and 5 = superior). Patients' weight and abdominal circumference, area, and anteroposterior and transverse diameters were correlated with image quality of scans obtained at standard-dose and 50% reduced-dose CT. Statistical analysis of the data was performed using Wilcoxon's signed rank test. RESULTS: Overall, the image quality score was significantly higher (p < 0.005) on the scans obtained with standard-dose CT. No statistically significant difference in image quality was noted in the 50% reduced- and standard-dose CT scans in patients who weighed less than 180 lb, or 81 kg, (p > 0.05) and who had a transverse abdominal diameter of less than 34.5 cm (p > 0.05), an anteroposterior diameter of less than 28 cm (p > 0.05), a cross-sectional circumference of less than 105 cm (p > 0.05), and a cross-sectional area of less than 800 cm(2) (p > 0.05). Good interobserver agreement (p > 0.5) was found between the two reviewing radiologists. CONCLUSION: Abdominal CT scan quality appears to be acceptable even with a 50% reduction in radiation dose except in patients with large anthropometric measurements. A reduction in CT radiation dose is possible if the tube current is optimized for the patient's weight and abdominal dimensions.

Abdomen↗

PubMedDate not supplied

State of the art in adrenal imaging.

The purposes of this article were to outline the current state of adrenal imaging, to highlight new developments, and to review the current radiologic advances that provide improved functional and structural information about adrenal disorders.

Adrenal Gland Neoplasms↗

PubMedDate not supplied

Computed tomography radiation dose optimization: scanning protocols and clinical applications of automatic exposure control.

As multi-detector-row computed tomography (CT) technology evolves, manifold applications of CT scanning have been adopted in clinical practice and optimization of scanning protocols to comply with an "as low as reasonably achievable" radiation dose have become more complex. Automatic exposure control techniques, which have been recently introduced on most state-of-the-art CT equipment, aid in radiation dose optimization at a selected image quality. The present article reviews the fundamentals of automatic exposure control techniques in CT, along with the scanning protocols and associated radiation dose reduction.

Automation↗

PubMedDate not supplied

"Hot" spots in hybrid positron emission tomography/computed tomography scanning of the abdomen: protocols, indications, interpretation, responsibilities, and reimbursements.

Although introduction of hybrid positron emission tomography/computed tomography (PET/CT) scanners represents an important development in field of radiology, the alliance of functional imaging with structural imaging has raised many controversial issues. The present review describes some of the important issues in hybrid PET/CT such as specific indications, protocols that deliver diagnostic quality CT scans while ensuring radiation dose associated with hybrid PET/CT examination are minimized, and the feasibility, desirability, and timing of oral and intravenous contrast administration. The issues of clinical indications for hybrid PET/CT versus PET alone will be discussed as well as the role of the CT component (ie, for diagnosis or transmission source alone) are discussed. The logistics of hybrid PET/CT scan interpretation, including the roles of radiologists and nuclear medicine physicians, will be discussed. This review describes the pertinent medical literature and discusses our experience with suitable examples.

Abdomen↗

PubMedDate not supplied

Characterization of small liver lesions: Added role of MR after MDCT.

OBJECTIVE: The purpose of this study is to evaluate the added role of magnetic resonance imaging (MR) in characterizing subcentimeter focal liver lesion(s) detected on multidetector row helical computed tomography (MDCT). MATERIALS AND METHODS: A retrospective analysis was performed in 59 noncirrhotic patients with focal subcentimeter liver lesion(s) detected on a 4- or 16-slice MDCT. All patients had a gadolinium enhanced liver MR on 1.5-T systems within 6 weeks after MDCT. Imaging diagnosis was graded on an ordinal scale of 0-5 (0, normal; 1, definitely benign; and 5, definitely malignant). The final diagnosis was established either by histopathology or follow-up imaging for a period of at least 6 months. Receiver operating characteristic analysis was performed to compare the performances of MDCT and MR in characterization of subcentimeter liver lesions. RESULTS: A total of 178 lesions were detected on MDCT in 59 patients. Of these lesions, 129 (72.5%) lesions were benign and the remaining 49 were malignant. The sensitivity, specificity, positive predictive value, and negative predictive value in differentiation of benign from malignant lesions on MDCT were 81.2%, 77.3%, 60.5%, 90.6 % and on MR were 83.3%, 97.5%, 92.1%, and 94.4 %, respectively. Comparative receiver operating characteristic analysis showed an area under curve for MDCT = 0.76 and MR = 0.95 (P < 0.001). CONCLUSIONS: Liver MR has significantly higher accuracy for characterization of subcentimeter focal liver lesions discovered on MDCT.

Adult↗

PubMedDate not supplied

Distinguishing hepatic metastases from hemangiomas: qualitative and quantitative diagnostic performance through dual echo respiratory-triggered fast spin echo magnetic resonance imaging.

OBJECTIVE: To determine the relative value of qualitative (reader opinion) and quantitative (values derived from dual echo T2 fast spin echo [FSE]) measures in distinguishing hepatic metastases from hemangiomas. METHODS: Forty-nine patients with hemangiomas and 23 with metastases were studied with dual echo respiratory-triggered FSE and dynamic 2-dimensional spoiled gradient echo (GRE) imaging. Lesion T2 was estimated from signal intensity ratios on the first and second echoes. Two experienced radiologists independently evaluated groups of images based on 5 separate qualitative measures: first echo FSE, second echo FSE, first and second echo FSE, dynamic GRE, and all images together. RESULTS: The mean calculated T2s were 226 +/- 74 milliseconds for hemangiomas and 105 +/- 22 milliseconds for metastases (P < 0.001). A T2 cutoff of 130 milliseconds distinguished metastases from hemangiomas with a sensitivity of 94%, specificity of 91%, and accuracy of nearly 94%. There was no significant difference between the best quantitative measure and the best qualitative measure for either reader. CONCLUSION: Liver lesion T2 relaxation times calculated from dual echo FSE images provide information useful in discriminating metastases from hemangiomas, as does reader opinion.

Adult↗

PubMedDate not supplied

Importance and effects of altered workplace ergonomics in modern radiology suites.

The transition from a film-based to a filmless soft-copy picture archiving and communication system (PACS)-based environment has resulted in improved work flow as well as increased productivity, diagnostic accuracy, and job satisfaction. Adapting to this filmless environment in an efficient manner requires seamless integration of various components such as PACS workstations, the Internet and hospital intranet, speech recognition software, paperless electronic hospital medical records, e-mail, office software, and telecommunications. However, the importance of optimizing workplace ergonomics has received little attention. Factors such as the position of the work chair, workstation table, keyboard, mouse, and monitors, along with monitor refresh rates and ambient room lighting, have become secondary considerations. Paying close attention to the basics of workplace ergonomics can go a long way in increasing productivity and reducing fatigue, thus allowing full realization of the potential benefits of a PACS. Optimization of workplace ergonomics should be considered in the basic design of any modern radiology suite.

Asthenopia↗

PubMedDate not supplied

Adult intestinal intussusception: CT appearances and identification of a causative lead point.

The widespread application of computed tomography (CT) in different clinical situations has increased the detection of intussusception, particularly non-lead point intussusception, which tends to be transient. Consequently, determining the clinical significance of intussusception seen at CT poses a diagnostic challenge. Patients with intussusception may or may not be symptomatic, and symptoms can be acute, intermittent, or chronic, making clinical diagnosis difficult. In most cases, radiologists can readily make the correct diagnosis of intestinal intussusception by noting the typical bowel-within-bowel appearance at abdominal CT. However, the CT findings that help differentiate between lead point and non-lead point intussusception have not been well studied. Nevertheless, although there is considerable overlap of CT findings, when a lead mass is seen at CT as a separate and distinct entity vis-à-vis edematous bowel, it can be considered a reliable indicator of a lead point intussusception. Differentiating between lead point and non-lead point intussusception is important in determining the appropriate treatment and has the potential to reduce the prevalence of unnecessary surgery.

Adult↗

PubMedDate not supplied

Pearls and pitfalls in interpretation of abdominal and pelvic PET-CT.

The interpretation of images obtained in the abdomen and pelvis can be challenging, and the coregistration of positron emission tomographic (PET) and computed tomographic (CT) scans may be especially valuable in the evaluation of these anatomic areas. PET-CT represents a major technologic advance, consisting of generally complementary modalities whose combined strength tends to overcome their respective weaknesses. However, this combined functional-structural imaging approach raises a number of controversial questions and presents some unique interpretative challenges. Accurate PET-CT scan interpretation requires awareness of the various pitfalls associated with the imaging components, both individually and in combination. The results of recent PET-CT studies have been very encouraging, but larger prospective studies will be needed to establish optimal hybrid scanning protocols. Applying sound imaging principles, paying attention to detail, and staying abreast of advances in this exciting new modality are necessary for harnessing the full diagnostic power of abdominopelvic PET-CT.

Abdomen↗

PubMedDate not supplied

Correlation of patient weight and cross-sectional dimensions with subjective image quality at standard dose abdominal CT.

OBJECTIVE: We evaluated the association between patients' weight and abdominal cross-sectional dimensions and CT image quality. MATERIALS AND METHODS: We prospectively evaluated 39 cancer patients aged more than 65 years with multislice CT scan of abdomen. All patients underwent equilibrium phase contrast-enhanced abdominal CT with 4 slices (from top of the right kidney) obtained at standard tube current (240-280 mA). All other scanning parameters were held constant. Patients' weight was measured just prior to the study. Cross-sectional abdominal dimensions such as circumference, area, average anterior abdominal wall fat thickness and, anteroposterior and transverse diameters were measured in all patients. Two subspecialty radiologists reviewed randomized images for overall image quality of abdominal structures using 5- point scale. Non-parametric correlation analysis was performed to determine the association of image quality with patients' weight and cross-sectional abdominal dimensions. RESULTS: A statistically significant negative linear correlation of 0.46, 0.47, 0.47, 0.58, 0.56, 0.54, and 0.56 between patient weight, anterior abdominal fat thickness, anteroposterior and transverse diameter, circumference, cross-sectional area and image quality at standard scanning parameters was found (p<0.01). CONCLUSION: There is a significant association between image quality, patients' weight and cross-sectional abdominal dimensions. Maximum transverse diameter of the abdomen has the strongest association with subjective image quality.

Aged↗

PubMedDate not supplied

Pituitary apoplexy precipitating diabetes insipidus.

OBJECTIVE: To describe a case of pituitary apoplexy complicated by diabetes insipidus and to review management of patients with pituitary apoplexy and water excretion disturbances associated with transsphenoidal surgery. METHODS: We describe clinical, laboratory, and radiologic findings in a patient with pituitary apoplexy and central diabetes insipidus. RESULTS: A 74-year-old woman presented with severe headache and sudden loss of vision for 12 hours, accompanied by thirst and frequent urination. Visual field examination demonstrated bitemporal hemianopsia. Her laboratory findings were significant for a serum sodium level of 152 mEq/L and urine specific gravity of <1.005. A magnetic resonance imaging scan of her pituitary gland identified a 3.5-cm suprasellar mass compressing the optic chiasm. She subsequently underwent transsphenoidal pituitary surgery with subtotal resection of this mass. Microscopic evaluation of tumor tissue revealed a pituitary adenoma with evidence of recent infarct and hemorrhage. Her clinical and biochemical course was consistent with the triphasic response that may occur after pituitary surgery related to damage to the hypothalamus and supraopticohypophyseal tract. CONCLUSION: Pituitary apoplexy may be rarely associated with diabetes insipidus.

Adenoma↗

PubMedDate not supplied

A malignant aldosteronoma.

OBJECTIVE: To describe a case of primary aldosteronism due to an adrenocortical carcinoma (ACC) and highlight the need for thorough long-term follow-up. METHODS: We present the clinical, laboratory, radiologic, and pathologic findings in a patient with ACC and review the related literature. RESULTS: A 52-year-old woman with a history of hypertension and hypokalemia was referred for evaluation of a 6-cm adrenal mass. Her biochemical studies revealed a serum aldosterone-to-renin ratio of 52 without evidence of cortisol, catecholamine, or androgen excess. She underwent surgical resection of this mass, and histologic analysis showed a focally brisk mitotic rate but no evidence of capsular or vascular invasion. In light of these findings, the biologic nature of the tumor was difficult to predict. Thus, it was thought to be an adrenocortical neoplasm. The patient underwent follow-up clinically, biochemically, and with interval computed tomography. Nine years later, hypertension and hypokalemia redeveloped, and she was found to have metastatic ACC. CONCLUSION: ACC can generally be reliably diagnosed; however, in some cases, the true biologic behavior is difficult to predict. We emphasize the importance of careful clinical, biochemical, and radiologic surveillance in these difficult cases because surgical resection provides the best opportunity for cure in patients with adrenal cancer.

Adrenal Cortex Neoplasms↗