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K A Kvistad

Publications and source records attributed to K A Kvistad.

17 recordsLinked to original sources
PubMed2003

New intravascular contrast agent applied to dynamic contrast enhanced MR imaging of human breast cancer.

PURPOSE: To evaluate the feasibility of using dynamic contrast-enhanced MR imaging with a new intravascular contrast agent in grading human breast cancer. MATERIAL AND METHODS: 23 patients with 27 breast tumors (21 carcinomas and 6 fibroadenomas) were examined with dynamic MR imaging after administration of Clariscan, an iron oxide nanoparticle with large T1 relaxivity and a long plasma half life. A 3D T1-weighted gradient echo sequence with an acquisition time of 60 s was repeated at regular intervals of 3-5 min before and up to 1 h after injection of 2 mg/kg b.w. of Clariscan. The endothelial transfer constant, Kps, which reflects overall vascular permeability, and the fractional plasma volume, fPV, were estimated from time-intensity curves acquired from three separate regions of interest (ROIs): whole tumor, a permeability hot spot, and a blood volume hot spot. Kps and fPV were compared to the results of histologic tumor grading (Scarff-Bloom-Richardson, SBR) and microvascular density, MVD. RESULTS: A statistically significant correlation between the MR-derived Kps parameters and the SBR score was obtained for the whole tumor ROI (R = 0.70), and for the permeability hot spot ROIs (R = 0.67). A correlation between fPV and SBR was detected for the blood volume hot spot ROIs (R = 0.48). There was no statistically significant correlation between Kps or fPV with MVD. CONCLUSION: The results support the hypothesis that dynamic MR with the intravascular contrast agent Clariscan may be used for non-invasive tumor grading.

Breast Neoplasms↗
PubMed2001

External standard method for the in vivo quantification of choline-containing compounds in breast tumors by proton MR spectroscopy at 1.5 Tesla.

Quantification of choline-containing compounds observed with (1)H MRS of breast tumors is of interest since such compounds have been linked to malignancy. Experiments were performed at 1.5 T with an external standard containing phosphocholine for calibration. In phantom studies, good precision was achieved after correction for T(1)/T(2) effects. T(2) values for choline were estimated for two breast cancer patients. A choline concentration of 2.0 mM was calculated for a third patient, a result comparable to in vitro findings. Magn Reson Med 46:189-192, 2001.

Breast Neoplasms↗
PubMed2001

Feature extraction and classification of dynamic contrast-enhanced T2*-weighted breast image data.

UNLABELLED: The relatively low specificity of dynamic contrast-enhanced T1-weighted magnetic resonance imaging (MR) imaging of breast cancer has lead several groups to investigate different approaches to data acquisition, one of them being the use of rapid T2*-weighted imaging. Analyses of such data are difficult due to susceptibility artifacts and breathing motion. MATERIALS AND METHODS: One-hundred-twenty-seven patients with breast tumors underwent MR examination with rapid, single-slice T2*-weighted imaging of the tumor. Different methods for classifying the image data set using leave-one-out cross validation were tested. Furthermore, a semi-automatic region of interest (ROI) definition tool was presented and compared with manual ROI definitions from a previous study. Finally, pixel-by-pixel analysis was done and compared with ROI analysis. The analyses were done with and without noise reduction. RESULTS: The minimum enhancement parameter was the most robust and accurate of the parameters tested. The semi-automatic ROI definition method was fast and produced similar results as the manually defined ROIs. Noise reduction improved both sensitivity and specificity, but the improvement was not statistically significant. The pixel-based analysis methods used in the present study did not improve classification results. CONCLUSIONS: Analysis of T2*-weighted breast images can be done in a rapid and robust manner by using semi-automatic ROI definition tools in combination with noise reduction. Minimum enhancement gives an indication of malignancy in T2*-weighted imaging.

Adenocarcinoma↗
PubMed2000

[Diagnosis of breast diseases with magnetic resonance tomography].

Magnetic resonance imaging (MRI) of the breast is currently used for evaluation of both parenchymal disease and silicone gel implants. MRI is widely recognised as the most accurate imaging method for evaluation of breast implant integrity. Knowledge of the MRI appearance of the different types of implants and the possible complications of their use is important for diagnosis in these patients. The use of contrast-enhanced MRI in breast cancer diagnosis has been investigated thoroughly during the last decade. It is a sensitive imaging method to detect breast pathology, and may have an important diagnostic impact in carefully selected patient groups. The development of new MR techniques may improve the utility of MR in breast cancer diagnosis, treatment and research.

Biopsy↗
PubMed2000

Axillary lymph node metastases in breast cancer: preoperative detection with dynamic contrast-enhanced MRI.

Metastatic involvement of axillary lymph nodes is one of the most important prognostic variables in breast cancer. The aim of our work was to study the value of dynamic contrast-enhanced MR imaging in revealing axillary lymph node metastases from breast cancer. A total of 65 patients with invasive breast cancer treated with axillary lymph node dissection were preoperatively evaluated by MRI. T1-weighted dynamic contrast-enhanced 3D images were acquired using a coil covering the breast and the axilla. The dynamic contrast enhancement, size, and morphology of the axillary lymph nodes were registered. Histopathological examination revealed axillary lymph node metastases in 24 patients. When using a signal intensity increase in the lymph nodes of >100% during the first postcontrast image as a threshold for malignancy, 57 of 65 patients were correctly classified (sensitivity 83%, specificity 90%, accuracy 88%). These results were not improved when lymph node size and morphology were used as additional criteria. Axillary lymph nodes can be evaluated as a part of an MR-mammography study without substantial increase in examination time, and provide the surgeon with knowledge about the localization of possible metastatic lymph nodes.

Adult↗
PubMed2000

Breast lesions: evaluation with dynamic contrast-enhanced T1-weighted MR imaging and with T2*-weighted first-pass perfusion MR imaging.

PURPOSE: To evaluate the diagnostic value of an imaging protocol that combines dynamic contrast-enhanced T1-weighted magnetic resonance (MR) imaging and T2*-weighted first-pass perfusion imaging in patients with breast tumors and to determine if T2*-weighted imaging can provide additional diagnostic information to that obtained with T1-weighted imaging. MATERIALS AND METHODS: One hundred thirty patients with breast tumors underwent MR imaging with dynamic contrast-enhanced T1-weighted imaging of the entire breast, which was followed immediately with single-section, T2*-weighted imaging of the tumor. RESULTS: With T2*-weighted perfusion imaging, 57 of 72 carcinomas but only four of 58 benign lesions had a signal intensity loss of 20% or more during the first pass, for a sensitivity of 79% and a specificity of 93%. With dynamic contrast-enhanced T1-weighted imaging, 64 carcinomas and 19 benign lesions showed a signal intensity increase of 90% or more in the first image obtained after the administration of contrast material, for a sensitivity of 89% and a specificity of 67%. CONCLUSION: T2*-weighted first-pass perfusion imaging can help differentiate between benign and malignant breast lesions with a high level of specificity. The combination of T1-weighted and T2*-weighted imaging is feasible in a single patient examination and may improve breast MR imaging.

Adult↗
PubMed1999

Characterization of neoplastic and normal human breast tissues with in vivo (1)H MR spectroscopy.

The purpose of this study was to evaluate whether the detection of choline-containing compounds in in vivo (1)H magnetic resonance spectroscopy (MRS) of breast lesions is specific for carcinomas, whether a choline peak in in vivo (1)H MRS can be detected under physiological conditions of increased metabolism in breast parenchyma, and whether analysis of lipid signals can differentiate between various breast lesions and tissues. Forty patients and volunteers were examined with in vivo (1)H MR spectroscopy. Three spectra with identical localization but increasing echo times were obtained. Choline-containing compounds were detected in 9 of 11 carcinomas and in 2 of 11 benign lesions. A choline signal was also detected in five of seven volunteers who were breast-feeding at the time of examination, demonstrating that choline compounds can be detected by in vivo (1)H MRS in breast tissue under physiological conditions. Analysis of lipid signals did not contribute to differentiation between various breast lesions and tissues. J. Magn. Reson. Imaging 1999;10:159-164.

Adult↗
PubMed1999

Applications of neural network analyses to in vivo 1H magnetic resonance spectroscopy of epilepsy patients.

A total of 67 in vivo water-suppressed proton magnetic resonance spectra of the temporal lobes were recorded from 15 patients with long standing temporal lobe epilepsy and 13 healthy volunteers. Conventional data analysis indicated slightly lower N-acetyl aspartate levels in epileptic patients compared with controls. For further analysis of data, a spectral region (4.0-1.5 ppm) was used as input for artificial neural network analysis. Correct classification of spectra was obtained in 66 out of 67 cases, disregarding from which side of the brain the spectra were recorded. The ability of the trained network to recognize spectra recorded both contalaterally and ipsilaterally to the epileptic focus strongly indicates bilateral metabolic changes. Artificial neural networks could also be trained to recognize whether the spectra were recorded from the ipsilateral or contralateral side of the epileptic focus, indicating that neural network analysis of in vivo proton MR spectra can be used as an additional tool for pre-surgical lateralization of seizure foci.

Adolescent↗
PubMed1999

Differentiating benign and malignant breast lesions with T2*-weighted first pass perfusion imaging.

PURPOSE: Invasive breast carcinomas and fibroadenomas are often difficult to differentiate in dynamic contrast-enhanced T1-weighted MR imaging of the breast, because both tumors can enhance strongly after contrast injection. The purpose of this study was to evaluate whether the addition of T2*-weighted first pass perfusion imaging can increase the differentiation of malignant from benign lesions. MATERIAL AND METHODS: Nine patients with invasive carcinomas and 10 patients with contrast enhancing fibroadenomas were examined by a dynamic contrast-enhanced T1-weighted 3D sequence immediately followed by a single slice T2*-weighted first pass perfusion sequence positioned in the contrast-enhancing lesion. RESULTS: The carcinomas and the fibroadenomas were impossible to differentiate based on the contrast enhancement characteristics in the T1-weighted sequence. The signal loss in the T2*-weighted perfusion sequence was significantly stronger in the carcinomas than in the fibroadenomas (p = 0.0004). CONCLUSION: Addition of a T2*-weighted first pass perfusion sequence with a high temporal resolution can probably increase the differentiation of fibroadenomas from invasive carcinomas in contrast-enhanced MR imaging of the breast.

Adult↗
PubMed1999

Determination of Hounsfield value for CT-based design of custom femoral stems.

Ct and advanced computer-aided design techniques offer the means for designing customised femoral stems. Our aim was to determine the Hounsfield (HU) value of the bone at the corticocancellous interface, as part of the criteria for the design algorithm. We obtained transverse CT images from eight human cadaver femora. The proximal femoral canal was rasped until contact with dense cortical bone was achieved. The femora were cut into several sections corresponding to the slice positions of the CT images. After obtaining a computerised image of the anatomical sections using a scanner, the inner cortical contour was outlined and transferred to the corresponding CT image. The pixels beneath this contour represent the CT density of the bone remaining after surgical rasping. Contours were generated automatically at nine HU levels from 300 to 1100 and the mean distance between the transferred contour and each of the HU-generated contours was computed. The contour generated along the 600-HU pixels was closest to the inner cortical contour of the rasped femur and therefore 600 HU seem to be the CT density of the corticocancellous interface in the proximal part of cadaver femora. Generally, femoral bone with a CT density beyond 600 HU is not removable by conventional reamers. Thus, we recommend the 600 HU threshold as one of several criteria for the design of custom femoral implants from CT data.

Adult↗
PubMed1997

[Magnetic tomography in diagnosis of breast implant rupture].

At least 20,000 Norwegian women have silicone breast implants, either for breast augmentation or for reconstruction. One of the complications associated with breast implants is rupture of the implants. Magnetic resonance imaging (MRI) has been shown to be the most accurate imaging modality for evaluating the integrity of breast implants. Recognition of the different types of implants and the appearance of normal implants on MRI is very important for distinguishing these from intracapsular and extracapsular ruptures. Examples are shown of MRI findings in normal and ruptured implants.

Breast Implants↗
PubMed1995

Femoral anteversion measured by ultrasound and CT: a comparative study.

Both computed tomography (CT) and ultrasonography have been used successfully to estimate the femoral anteversion (AV) angle. In this study, AV angles in 20 human adult femurs were determined by ultrasonography and CT and the measurements compared. On CT the real AV angle was measured as the angle between the head-neck centreline and the posterior condylar plane. In addition, the angle between the anterior head-trochanter (HT) tangent and the posterior condylar plane was determined. The latter angle was also measured by ultrasonography using the tilted transducer technique. The mean interobserver variation in the ultrasound measurements was 1.9 degrees. We found ultrasonography to correlate very well with CT, both when comparing with the HT angle (r = 0.95) and with the AV angle (r = 0.93). The HT angle was on average 4 degrees greater than the AV angle. In this study the accuracy of ultrasonography was +/- 5 degrees and the method is recommended for screening in patients with rotational disorders of the femur.

Adult↗
PubMed1991

[Atlanto-axial rotatory fixation. Current diagnosis in torticollis].

Atlantoaxial rotatory fixation is a disorder which must be considered in persistent torticollis. The disorder occurs mainly in children and young adults. The usual etiological factors are traumas or infections of the upper respiratory tract, but the onset may also be spontaneous. The pathogenesis of the fixation is poorly understood. We describe three patients with atlantoaxial rotatory fixation and demonstrate the usefulness of computerized tomography in the diagnosis of this condition. We recommend a posterior atlantoaxial fusion if conservative treatment fails to reduce the rotatory fixation.

Adult↗
PubMed1991

Computed tomography measurements of the acetabulum in adult dysplastic hips: which level is appropriate?

A study has been performed to evaluate whether one or several levels are needed with computed tomography (CT) study to provide sufficient information regarding anteversion and acetabular support to the femoral head. A total of 23 hips in 14 adults with uni- or bilateral congenital hip dysplasia (center-edge angle less than 20 degrees) were assessed by obtaining 5-mm contiguous CT slices and performing acetabular measurements at four levels. Both anterior and posterior acetabular supports as quantified by the anterior and posterior acetabular sector angles were significantly lower than normal at all levels. The sector angles increased in the proximal cuts, whereas the acetabular anteversion increased caudally. Because no important additional information was gained by measuring at different levels, we conclude that CT study at one level is sufficient for acetabular measurements and suggest that the slice through the center of the femoral head is the most appropriate one.

Acetabulum↗
PubMedDate not supplied

Acetabular angles and femoral anteversion in dysplastic hips in adults: CT investigation.

Transpelvic CT was used to quantify the relationship between the acetabulum and proximal femur in 21 adult patients (33 hips) with congenital hip dysplasia (defined by a center edge angle of less than 20 degrees). The anterior and posterior acetabular sector angles (AASA and PASA) were measured, as well as the degree of acetabular and femoral anteversion. The results demonstrated deficient anterior acetabular support (i.e., decreased AASA) in approximately two-thirds of the dysplastic hips and reduced posterior support (i.e., decreased PASA) in one-third. The acetabular anteversion was normal. The femoral anteversion. however, was greater than normal in most hip. As important additional information is obtained by CT compared with conventional radiography, CT is recommended when operative procedures aimed at preventing or postponing osteoarthrosis are considered.

Acetabulum↗
PubMedDate not supplied

Classification of in vivo 1H MR spectra from breast tissue using artificial neural networks.

BACKGROUND: The study was designed in order to investigate whether artificial neural networks could be used for analysis of in vivo magnetic resonance (MR) spectra from breast cancer patients. MATERIALS AND METHODS: In vivo 1H MR spectra with three different echo times (TE 135, 350 and 450 msec) were acquired from patients with benign and malignant breast lesions and from healthy volunteers, of whom some were breast-feeding. A spectral region (4.0-1.5 ppm) was used as input for artificial neural network analysis, for the attempted classification of the data into different groups. RESULTS: Data recorded at all three echo times were necessary to obtain the best results. Furthermore, malignant tissue was differentiated from benign tumours using this approach, whereas benign tumours were poorly separated from healthy tissue. CONCLUSION: The results presented here indicate that in vivo MR spectroscopy in conjunction with neural network analysis might be useful for the evaluation of breast lesions.

Breast↗