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PubMedDate not supplied

An enhanced electrical impedance imaging algorithm for hyperthermia applications.

Electrical impedance imaging is a technique which is under investigation as a noninvasive method of tracking subsurface temperature distributions and/or associated cellular response during hyperthermia. In previous work, a finite element image reconstruction algorithm for converting surface potential distributions recorded at discrete electrode positions into spatial maps of conductivity values was developed. This paper reports on a series of significant improvements in the basic image reconstruction approach. Specifically, the ability to recover both the resistive and capacitive components of tissue electrical impedance have been incorporated. In addition, the image enhancement schemes of (1) total variation minimization, (2) dual meshing, and (3) spatial low-pass filtering, have been added. Through a series of simulation studies involving both phantom-like and clinically-relevant geometries having discrete regions and continuously-varying electrical property profiles, a significantly improved ability to recover spatial images of electrical properties in the impedance imaging context is demonstrated. The results show that the new algorithm is much more tolerant of measurement noise with levels up to 1% causing relatively modest degradations in image quality (compared to 0.1% which was needed previously in order to produce high quality images). The recovered electrical properties, themselves, both resistive and capacitive, are also found to be quantitative in value with errors in the 10-20% range occurring in the majority of cases, although deviations can reach 40% or more when noise levels as high as 10% are used. Temperature estimation simulations show that maximum temperature errors are significantly reduced (to approximately 2 degrees C relative to more than 10 degrees C in previous thermal simulations) with the new algorithm; however, temperature accuracies of better than 0.5 degree C on average are still found to be difficult to achieve with electrical impedance imaging even when the enhanced image reconstruction approach is used.

Algorithms↗

PubMedDate not supplied

Detection of brain metastasis: comparison of Turbo-FLAIR imaging, T2-weighted imaging and double-dose gadolinium-enhanced MR imaging.

The purpose of this study was to compare Turbo-FLAIR imaging, T2-weighted imaging, and double-dose gadolinium-enhanced MR imaging in the detection of brain metastasis. Using the three sequences, 20 consecutive patients with brain metastases were prospectively studied with a 1.5-Tesla system. Three independent, blinded readers assessed the images for the presence, size, number, and location of metastatic lesions. In the detection of large lesions (> 0.5 cm), Turbo-FLAIR imaging (38/48, 79%) was not significantly different from gadolinium-enhanced imaging (42/48, 88%) (p = 0.273). T2-weighted imaging (31/48, 65%), however, was inferior to gadolinium-enhanced imaging (p < 0.05). There was no difference between Turbo-FLAIR imaging and gadolinium-enhanced imaging in the accuracy of detecting solitary brain metastasis (4/4, 100%). In conclusion, Turbo-FLAIR imaging is a useful, noninvasive screening modality for brain metastasis. Its use may lead to cost savings in the diagnosis of brain metastases and may impact positively the cost-effectiveness of treatment.

Brain↗

PubMed2003

Inflammatory myofibroblastic tumor of the hepatobiliary system: report of MR imaging appearance in four patients.

The purpose of this report is to describe the magnetic resonance (MR) imaging features of hepatic inflammatory myofibroblastic tumor (IMT). Two observers retrospectively analyzed images from six MR imaging examinations in four consecutive patients. Tumor location, size, extent, morphology, and number; signal intensity on nonenhanced images; enhancement pattern on serial gadolinium-enhanced images; duct wall thickness; and presence of biliary dilatation, vascular invasion, and lymphadenopathy were assessed. MR imaging findings were compared with histologic findings. On MR images, hepatic IMT manifested as a mass-like lesion in two patients and an area of periportal soft-tissue infiltration in three; one patient had both patterns. Because periportal infiltration is a common feature in both IMT and other malignant tumors of the porta hepatis, histologic examination should be considered before diagnosis and treatment.

Adult↗

PubMed1999

Contrast-enhanced magnetic resonance imaging in a nontraumatic rabbit osteonecrosis model.

We investigated early osteonecrosis using in vivo magnetic resonance imaging in a nontraumatic rabbit model of serum-sickness osteonecrosis in which osteonecrosis was induced after two intravenous injections of horse serum with a 3-week interval. One week (group A, 17 rabbits) and 3 weeks (group B, 13 rabbits) after the second serum injection, coronal magnetic resonance images of the femur were obtained and it was removed for histological study. Some of the necrotic lesions in the diaphysis were detected on T1-weighted, T2-weighted, or fat-suppression T1-weighted images (six of 24 necrotic lesions in group A and 16 of 18 in group B), and all of the necrotic lesions in the epiphysis, metaphysis, and diaphysis were detected on T1-weighted or fat-suppression T1-weighted images enhanced with gadolinium-diethylene triamine pentaacetic acid. All focal homogeneous enhanced areas on T1-weighted or fat suppression T1-weighted images corresponded to necrotic lesions (22 of 24 necrotic lesions in group A and 18 of 18 in group B); the contours of the enhanced areas were displayed more clearly on the fat-suppression T1-weighted than on the T1-weighted images. The fat-suppression T1-weighted image enhanced with gadolinium-diethylene triamine pentaacetic acid was thus the most sensitive and specific of five kinds of magnetic resonance images for the detection of early necrotic lesions. The results suggest that this image may be useful for early diagnosis of clinical osteonecrosis and for obtaining information about the pathomechanism of osteonecrosis.

Animals↗

PubMedDate not supplied

Prominent dural enhancement adjacent to nonmeningiomatous malignant lesions on contrast-enhanced MR images.

Prominent dural enhancement was noted in 10 (16%) of 61 superficial malignant intracranial tumors studied with contrast-enhanced MR imaging during a 2-year period. Included were six glioblastomas, three parenchymal metastases, and one case of dural metastasis. Seven patients had surgery. In four, there was extensive leptomeningeal invasion in the center of the lesion. In two of these lesions there was firm attachment of the center of the tumor to the dura, but without dural invasion despite extensive external carotid artery supply to the tumor in one case. In two cases the overlying dura was normal, and there was no leptomeningeal tumoral invasion. In the case of dural metastasis, huge nodular lesions were present along the inner aspect of the dura. In none of the cases did prominent dural enhancement adjacent to the tumor correspond with tumoral invasion or extension to the dura. Prominent dural enhancement on contrast-enhanced MR images appears to be much less frequent in malignant tumor than in meningioma, where it is seen in up to 60% of the cases. We believe this finding is more likely to represent reactive changes of the dura than tumoral invasion.

Brain Neoplasms↗

PubMed1990

Contrast-enhanced magnetic resonance imaging of tumor-bearing mice treated with human recombinant tumor necrosis factor alpha.

Pharmacological effects of recombinant human tumor necrosis factor alpha (TNF) were studied in a mouse fibrosarcoma model using magnetic resonance imaging enhanced with a macromolecular contrast agent, albumin(gadolinium-diethylenetriamine pentaacetic acid)35. TNF was administered i.v. in a dose of 150 micrograms/kg, 60 to 80 min prior to imaging. Contrast-enhanced and nonenhanced magnetic resonance images of TNF-treated (n = 10) and untreated (n = 8) Meth A fibrosarcomas were obtained at 2.0 Tesla using T1-weighted spin-echo pulse sequences. Serial images spanning an interval of 60 to 120 min after TNF administration showed that the TNF-treated tumors enhanced significantly more overall than did untreated tumors (43% versus 31%). The most marked differential tumor enhancement was observed in the tumor rim (59% versus 40%). Nontumorous tissue, including muscle and brain, revealed no significant enhancement differences between TNF-treated animals and controls. The observed tumor enhancement corresponded strongly with Evans blue staining; the TNF-treated tumors stained deep blue, while untreated tumors and normal tissues observed did not stain. The different enhancement and Evans blue staining patterns between TNF-treated tumors and untreated tumors are attributed to TNF-induced changes in tumor capillary integrity. The data indicate that TNF effects on tumors include an increased capillary permeability for macromolecules at early times after administration. The ability to detect changes in capillary permeability in vivo using contrast-enhanced magnetic resonance imaging may prove to be clinically useful to monitor tumor response to TNF.

Animals↗

PubMed2005

Enhanced viability imaging: improved contrast in myocardial delayed enhancement using dual inversion time subtraction.

In delayed contrast-enhanced MRI for the assessment of myocardial viability, the TI time in a gated inversion-recovery segmented gradient echo sequence is usually selected to null signal from normal myocardium. Although this TI time generates good contrast between the enhancing infarcted tissue and normal myocardium, there is usually less contrast between the infarct and the blood pool. A subtractive technique utilizing two acquisitions at a long and short TI time is proposed to improve the delineation between infarct-blood and infarct-myocardium. The concept was demonstrated in six mongrel dogs with reperfused myocardial infarction. Infarct-normal myocardium contrast (signal difference) using the proposed enhanced viability imaging (ENVI) technique was 142 +/- 50% (P < 0.001) that of standard magnitude inversion recovery (IR), while at the same TI time for the primary image, infarct-blood contrast, was 247 +/- 136% (P < 0.002) that of magnitude IR. Accounting for increased noise due to the subtraction, signal difference-to-noise ratios (SDNR) did not show a significant change for infarct-myocardium but infarct-blood SDNR for ENVI was 174 +/- 105% that of magnitude-IR (P < 0.03). Thus, marked improvement in the delineation of the infarcted zone was noted over a range of TI times.

Animals↗

PubMed1996

Statistical methods in the Fourier domain to enhance and classify images.

A mathematical model, for which rigorous methods of statistical inference are available, is described and techniques for image enhancement and linear discriminant analysis of groups are developed. Since the gray values of neighboring pixels in tomographically produced medical images are spatially correlated, the calculations are carried out in the Fourier domain to insure statistical independence of the variables. Furthermore, to increase the power of statistical tests the known spatial covariance was used to specify constraints in the spectral domain. These methods were compared to statistical procedures carried out in the spatial domain. Positron emission tomography (PET) images of alcoholics with organic brain disorders were compared by these techniques to age-matched normal volunteers. Although these techniques are employed to analyze group characteristics of functional images, they provide a comprehensive set of mathematical and statistical procedures in the spectral domain that can also be applied to images of other modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI).

Aged↗

PubMed1997

MR imaging of enhancing intraosseous disk herniation (Schmorl's nodes).

OBJECTIVE: This study was conducted to show vascularization of Schmorl's nodes with enhanced MR imaging and to correlate this finding with clinical complaints. MATERIALS AND METHODS: Retrospectively, 412 gadopentetate dimeglumine-enhanced MR imaging examinations of the lumbar and thoracic spine of 372 patients were reviewed for Schmorl's nodes, vascularization of Schmorl's nodes, and associated bone marrow edema. Sagittal T2-weighted spin-echo and unenhanced and enhanced T1-weighted spin-echo images with and without fat suppression were evaluated in symptomatic and asymptomatic patients. RESULTS: Of the 372 patients, 142 (38%) had 341 Schmorl's nodes. Gadopentetate dimeglumine-enhanced MR imaging revealed vascularized tissue in 30 Schmorl's nodes of 23 patients (mean age of patients, 53 years old). Associated bone marrow edema was found in nine of 30 vascularized Schmorl's nodes. The mean diameter (8.2 mm) of the nine vascularized Schmorl's nodes that were surrounded by bone marrow edema was significantly (p < .05) greater than the mean diameter (6.4 mm) of the 21 vascularized Schmorl's nodes that had no bone marrow edema. The vascularized Schmorl's nodes were significantly (p < .05) smaller in the seven asymptomatic patients (mean, 5.2 mm) than in the 23 patients with back pain (mean, 7.9 mm). We saw bone marrow edema adjacent to Schmorl's nodes less frequently in asymptomatic patients (one of seven) than in symptomatic patients (10 of 23). CONCLUSION: Vascularized Schmorl's nodes were larger and more frequently associated with bone marrow edema in patients with back pain than in asymptomatic patients. Enhanced MR images of Schmorl's nodes revealed vascularity, which was not shown on unenhanced MR images.

Adult↗

PubMed2002

Accuracy of abnormal paraspinal muscle findings on contrast-enhanced MR images as indirect signs of unilateral cervical root-avulsion injury.

PURPOSE: To evaluate the accuracy of abnormal magnetic resonance (MR) findings in the paraspinal muscles as indirect signs of nerve-root avulsion injury. MATERIALS AND METHODS: Forty-three consecutive patients suspected of having unilateral root-avulsion injury underwent MR imaging and were evaluated. Paraspinal muscles were evaluated for abnormal signal intensity on T1- and T2-weighted images, abnormal enhancement on images obtained after contrast material enhancement, and muscle volume loss. MR images were interpreted independently by two observers for interobserver variability. MR findings were compared with findings of root continuity, determined with a combination of surgery and clinical evaluation. Sensitivities, specificities, and kappa values of the findings were calculated. RESULTS: Sensitivities of MR findings in the paraspinal muscles indicating root-avulsion injury were 88% (36 of 41 patients) for abnormal enhancement, 83% (34 of 41 patients) for high signal intensity on T2-weighted images, 37% (15 of 41 patients) for high signal intensity on T1-weighted images, and 71% (29 of 41 patients) for muscle volume loss. Specificities for all findings were 100% (two of two patients). Of the paraspinal muscles, findings in the multifidus muscle were the most accurate and provided the highest interobserver agreement (kappa = 0.81). CONCLUSION: Contrast material-enhanced abnormal MR findings in the paraspinal muscles are accurate in indicating root-avulsion injuries, and abnormal enhancement in the multifidus muscle is the most accurate among paraspinal muscle findings.

Adolescent↗

PubMed2006

Diagnostic performance of stress perfusion and delayed-enhancement MR imaging in patients with coronary artery disease.

PURPOSE: To prospectively determine the accuracy of a combined magnetic resonance (MR) imaging approach (stress first-pass perfusion imaging followed by delayed-enhancement imaging) for depicting clinically significant coronary artery stenosis (> or = 70% stenosis) in patients suspected of having or known to have coronary artery disease (CAD), with coronary angiography serving as the reference standard. MATERIALS AND METHODS: The committee on human research approved the study protocol, and all participants gave written informed consent. This study was HIPAA compliant. Forty-seven patients (38 men and nine women; mean age, 63 years +/- 5.3 [standard deviation]) scheduled for coronary angiography were prospectively enrolled: 33 were suspected of having CAD (group A) and 14 had experienced a previous myocardial infarction and were suspected of having new lesions (group B). The MR imaging protocol included cine function, gadolinium-enhanced stress and rest first-pass perfusion MR imaging, and delayed-enhancement MR imaging. Myocardial ischemia was defined as a segment with perfusion deficit at stress first-pass perfusion MR imaging and no hyperenhancement at delayed-enhancement imaging. Myocardial infarction was defined as an area with hyperenhancement at delayed-enhancement imaging. RESULTS: One patient was excluded from analysis because of poor-quality MR images. Coronary angiography depicted significant stenosis in 30 of 46 patients (65%). In a per-vessel analysis (n = 138), stress first-pass perfusion MR imaging and delayed-enhancement imaging yielded sensitivity of 0.87, specificity of 0.89, and accuracy of 0.88, when compared with coronary angiography. The diagnostic accuracy of stress first-pass perfusion MR imaging and delayed-enhancement imaging was slightly better than that of stress and rest first-pass perfusion MR imaging in the entire population (0.88 vs 0.85), in group A (0.86 vs 0.82), and in group B (0.93 vs 0.90). CONCLUSION: Stress first-pass perfusion MR imaging followed by delayed-enhancement imaging is an accurate method to depict significant coronary stenosis in patients suspected of having or known to have CAD.

Aminophylline↗

PubMed1996

Image subtraction in gadolinium-enhanced MR imaging.

Image subtraction in gadolinium-enhanced MR imaging is a broadly applicable postprocessing technique that can be used with any field strength and T1-weighted sequence. This technique is typically a quick and efficient means of obtaining fat suppression that avoids the limitations of incomplete fat saturation due to field inhomogeneity and increased imaging times associated with conventional fat-suppression techniques. In particular, image subtraction may be valuable on lower strength magnetic field systems that lack effective chemical-shift fat-suppression techniques. Because source data are viewed in conjunction with subtracted images, image subtraction is unlikely to introduce errors in interpretation. By performing unenhanced and enhanced sequences in a manner amenable to image subtraction, radiologists should find this technique to be a useful and almost cost-free option.

Aged↗

PubMed2004

Accuracy of diagnosing occlusal caries using enhanced digital images.

OBJECTIVES: To compare the accuracy of detecting occlusal caries lesions on original images vs images digitally enhanced for sharpness, zoom and pseudocolour. METHODS: Four hundred images of 100 extracted third molars were examined for the presence or absence of occlusal caries by four observers, using a 5-point confidence scale. The observers had no prior knowledge of the distribution of the caries. The definitive diagnosis of caries was based on a histological assessment after sectioning the teeth. The diagnostic accuracy for each imaging mode was expressed by the area of the receiver operating characteristic (ROC) curve. Differences between the areas under the ROC curves were assessed using an analysis of variance. RESULTS: The original image had a mean ROC curve of 0.75 (95% confidence interval (CI) 0.65-0.85). The ROC curves for sharpness, zoom and pseudocolour were 0.73 (95% CI 0.63-0.83), 0.76 (95% CI 0.61-0.81) and 0.70 (95% CI 0.60-0.80), respectively. These differences were not statistically significant (P=0.96). The Cohen's kappa indicated good agreement among observers. CONCLUSIONS: In this in vitro study, the three enhanced images used did not affect the detection of occlusal caries.

Analysis of Variance↗

PubMed1991

Histologic basis for increased extraocular muscle enhancement in gadolinium-enhanced MR imaging.

Minimal to mild enhancement of skeletal muscles is normally seen on gadolinium-enhanced magnetic resonance images. The enhancement of the extraocular muscles is much more intense than that of other skeletal muscles. The authors investigated the structural features of extraocular muscles that contribute to this increased enhancement. After comparing samples of extraocular muscle and quadriceps muscle, the authors concluded that the rich vascularity and the prominence of extravascular space most probably cause extraocular muscles to demonstrate intense enhancement on gadolinium-enhanced images.

Gadolinium DTPA↗

PubMed1992

Osteomyelitis in children: gadolinium-enhanced MR imaging.

Fifteen pediatric patients with biopsy- or culture-proved nonspinal osteomyelitis were studied with magnetic resonance (MR) imaging. Osteomyelitis was acute in seven patients, subacute in three, and chronic in five. Four patients had subperiosteal abscesses, one had a large associated soft-tissue abscess, and one had an intraosseous (Brodie) abscess. Areas of active inflammation had decreased marrow signal intensity on T1-weighted images, increased signal intensity on T2-weighted images, and enhancement on T1-weighted images obtained after gadopentetate dimeglumine administration (n = 10). Abscesses were rim enhancing (n = 3) or not (n = 2) with gadolinium-enhanced MR imaging. Nonenhancing areas presumably represented necrotic material. Gadolinium-enhanced MR imaging assisted in definition of the presence and extent of nonvascularized fluid collections within the bone and/or adjacent soft tissues and the extent of bone involvement in patients with chronic osteomyelitis. It also helped guide surgical debridement of intraosseous disease (n = 7) and open or percutaneous drainage of subperiosteal or soft-tissue fluid collections (n = 5).

Abscess↗

PubMed1998

Half-dose gadolinium-enhanced MR imaging with magnetization transfer technique in brain tumors: comparison with conventional contrast-enhanced MR imaging.

OBJECTIVE: The purpose of this study was to determine whether half-dose enhanced MR imaging with magnetization transfer (MT) saturation can replace standard-dose enhanced MR imaging without MT saturation in patients who have brain tumors. SUBJECTS AND METHODS: Three sets of enhanced T1-weighted MR images were prospectively obtained for each of 25 patients with 32 brain tumors; the first conventional MR images without MT were obtained after administration of standard-dose (0.1-mmol/kg) gadopentetate dimeglumine. Within 1 week, patients underwent administration of one half-dose (0.05 mmol/kg) of the contrast medium, and then two sets of enhanced T1-weighted images were obtained with and then without MT. The degree of contrast enhancement was assessed qualitatively for all 32 tumors and quantitatively for 26 tumors. In the quantitative analysis, we compared mean values for tumor-brain contrast-to-noise ratios in three sets of images. RESULTS: The visual conspicuity of enhancing lesions in half-dose T1-weighted MR images with MT was comparable with that of standard-dose conventional T1-weighted MR images in 43% of cases including most extraaxial tumors. In approximately 75% of cases, the degree of enhancement of the lesions was similar for half-dose T1-weighted images obtained with and without MT. Overall, mean values for tumor-brain contrast-to-noise ratios were significantly lower in half-dose T1-weighted images with MT than in standard-dose T1-weighted images. Also, mean values for tumor-brain contrast-to-noise ratios were significantly higher in half-dose T1-weighted images with MT than in half-dose T1-weighted images without MT. CONCLUSION: Because half-dose enhanced MR imaging with MT yields enhancement comparable with that of standard-dose enhanced conventional MR imaging in less than 50% of cases, the former technique would replace the latter in only limited cases such as selected extraaxial tumors.

Adult↗

PubMed1991

Dynamic gadolinium-enhanced MR imaging of the spleen: normal enhancement patterns and evaluation of splenic lesions.

The authors studied the ability to improve detection of splenic lesions during suspended respiration with dynamic gadolinium-enhanced T1-weighted spin-echo magnetic resonance (MR) imaging. In the first phase of the study, normal splenic contrast material enhancement patterns were assessed in 10 control patients without splenic lesions. A heterogeneous signal intensity pattern was observed in 11 patients with splenic lesions during bolus injection of gadopentetate dimeglumine, with conversion to homogeneous enhancement 1 minute later. Mean splenic enhancement was 321% during bolus injection, with a rapid return toward baseline signal intensity thereafter. In the second phase, evaluation of 18 splenic lesions detected with contrast-enhanced computed tomography in 11 patients revealed that dynamic gadolinium-enhanced MR pulse sequences significantly improved lesion conspicuity and detectability compared with conventional T1-and T2-weighted pulse sequences. Contrast-to-artifact ratio measurements were 0.5, 3.7, and 9.3 for conventional T1-weighted, T2-weighted, and dynamic gadolinium-enhanced MR images, respectively.

Adult↗

PubMed2000

Test-bolus injection for optimization of arterial phase imaging during contrast-enhanced hepatic MR imaging.

Contrast enhancement during the dynamic MR imaging is important for the detection and characterization of focal liver lesions. The purpose of this study was to determine whether or not a timing examination with a injection of a 1.0-mL bolus of gadopentetate dimeglumine into the antecubital vein followed by rapid dynamic scanning and measurement of signal intensity of the aorta could help to obtain proper arterial-dominant phase images for the characterization of focal hepatic lesions during subsequent multiphase dynamic MR imaging. The imaging delay to acquisition of the first gadolinium-enhanced image for multiphase dynamic MR imaging was set to equal the time to peak aortic enhancement during the test examination. The first contrast-enhanced images of 80 patients with 160 focal liver lesions (hepatocellular carcinoma, n = 79; cavernous hemangioma, n = 51; metastatic tumor, n = 30) were then retrospectively reviewed. Peak aortic enhancement occurred between 10 and 28 seconds (mean, 16.5 seconds +/- 3.1) after starting the infusion of contrast material in 80 patients during the test-examination. Depending on the findings of intrahepatic vascular enhancement on the full-scale dynamic images, hepatic arterial phase (n = 11, 14%) or sinusoid phase (n = 65, 81%) imaging was obtained during the first gadolinium-enhanced acquisition in 76 (95%) of 80 patients. Three different lesions were well characterized and easily distinguished from each other (p < .0001) on the first-phase images depending on their enhancement pattern. In the majority of patients, timing examination with test-bolus injection was helpful in obtaining qualified images for the characterization of various focal lesions.

Adult↗