Postmortem magnetic resonance imaging as an adjunct to perinatal autopsy for renal-tract abnormalities.

The aim of this study was to compare postmortem magnetic resonance imaging (MRI) of the renal system with autopsy in perinatal and fetal deaths. 37 deaths were studied and renal abnormalities were found in five of these cases. Postmortem MRI provided information of diagnostic utility comparable to that obtained by autopsy.

Dynamic contrast enhanced MRI of the axilla in women with breast cancer: comparison with pathology of excised nodes.

Axillary lymph node status is the most important prognostic factor in breast cancer patients and is currently determined by surgical dissection. This study was performed to assess whether dynamic gadopentetate dimeglumine (Gd) enhanced MRI is an accurate method for non-invasive staging of the axilla. 47 women with a new primary breast cancer underwent pre-operative dynamic Gd enhanced MRI of the ipsilateral axilla. Lymph node enhancement was quantitatively analysed using a region of interest method. Enhancement indices and nodal area were compared with histopathology of excised nodes using a receiver operating characteristic (ROC) curve approach. 10 patients had axillary metastases pathologically and all had > or =1 lymph node with an enhancement index of >21% and a nodal area of >0.4 cm(2). 37 patients had negative axillary nodes pathologically. 20 of these had enhancement indices <21% and nodal areas <0.4 cm(2). Using this method, a sensitivity of 100%, a specificity of 56%, a positive predictive value of 38% and a negative predictive value of 100% could be achieved. Using this method of quantitative assessment, dynamic Gd enhanced MRI may be a reliable method of predicting absence of axillary nodal metastases in women with breast cancer, thereby avoiding axillary surgery in women with a negative MRI study.

Three-dimensional imaging of the postmortem fetus by MRI: early experience.

OBJECTIVE: The feasibility and significance of three-dimensional (3D) visualization of the postmortem fetus using magnetic resonance imaging (MRI) was investigated. METHODS: 3D reconstruction of sectional MRI data sets from 8 postmortem fetuses was performed. RESULTS: Fetal configurations and internal structures, both normal and pathological, were clearly demonstrated by 3D display. CONCLUSION: This new technique provides high quality fetal 3D images for postmortem morphological diagnosis and interactive visual teaching. It may eventually have applications in prenatal diagnosis and the preoperative simulation of fetal surgery.

Accuracy of T1 measurement in dynamic contrast-enhanced breast MRI using two- and three-dimensional variable flip angle fast low-angle shot.

In vivo T1 measurements, used to monitor the uptake of contrast agent by tissues, are typically performed as a first step in implementing compartmental analysis of contrast-enhanced breast magnetic resonance imaging (MRI) data. We have extended previously described methodology for in vivo T1 measurement (using a variable flip-angle gradient-recalled echo technique) to two-dimensional (2D), fast low-angle shot (FLASH). This approach requires computational modeling of slice-selective radiofrequency (RF) excitation to correct for nonrectangular slice profiles. The accuracy with which breast tissue T1 values can be measured by this approach is examined: T1 measurements from phantom and in vivo image data acquired with 2D and 3D FLASH imaging sequences are presented. Significant sources of error due to imaging pulse sequence quality and RF transmit field nonuniformity in the breast coil device that will have detrimental consequences for compartmental analysis are identified. Rigorous quality assurance programs with calibrated phantoms are thus recommended, to verify the accuracy with which T1 measurements are obtained.

Measurement of the emission profiles of cylindrical light diffusers using a video technique.

The uniformity of the emission profile produced by a cylindrical light diffuser is an important parameter for determining the light dose received by the target tissue during laser therapies such as photodynamic therapy (PDT) and interstitial laser photocoagulation (ILP). A technique originally used for determining the profile of a laser beam with a commercial video camera is adapted in order to measure the distribution of light from a cylindrical diffuser. The method can produce quantitative one-dimensional beam profiles in both the circumferential and axial direction of the light diffuser. The system allows the use of tissue phantoms that provide a convenient and effective method for comparing manufacturer's measurements often made in air with those to be expected in vivo. The technique is a quick and easy method for assessing light diffusers before treatment, and utilises readily available equipment that does not require specialist knowledge. Also, the response of the video camera facilitates the assessment of diffusers over a relatively broad optical spectrum, which encompasses the range of wavelengths currently used for both PDT (515-675 nm) and ILP (800-1064 nm).

Estimation of differential renal function in children with a prenatal diagnosis of unilateral pelvic dilatation.

PURPOSE: We compared the estimation of differential renal function by 99mtechnetium (Tc)-dimercapto-succinic acid (DMSA) and 99mTc-pentetic acid scintigraphic methods for followup of prenatally diagnosed unilateral renal pelvic dilatation. MATERIALS AND METHODS: We retrospectively analyzed differential renal function estimations calculated by static and dynamic methods in time matched test pairs that were included in the charts of 51 children monitored for prenatally diagnosed unilateral renal pelvic dilatation at our institution in a 5-year period. RESULTS: There were 96 test pairs with available archived raw data. Using the analytic method of assessment of agreement between the 2 tests, a 95% limit of agreement of +/-9% was calculated. Of the 96 pairs of tests the results of 94 revealed no significant difference. Subgroup analysis by patient age and operative intervention (13 postoperative pairs) also showed no difference in the results of the 2 tests. CONCLUSIONS: We established the 95% limits of agreement between 99mTc-DMSA and 99mTc-pentetic acid tests of differential renal function to be +/-9% discrepancy in 96 test pairs. During followup of prenatally diagnosed unilateral renal pelvic dilatation the assessment of differential renal function can be made by 99mTc-DMSA static or dynamic diuretic renography techniques. This interchangeability is consistent at all patient ages regardless of operative intervention. Since dynamic diuretic renography provides differential function and drainage data, using 99mTc-DMSA in this context is unnecessary and subjects patients to an unnecessary radiation burden.

Three-dimensional magnetic resonance imaging of the postmortem fetal heart.

Five postmortem fetuses were scanned by magnetic resonance (MR) imaging. Of eight three-dimensional (3D) data sets reconstructed on an MGI workstation, five sets demonstrated detailed 3D fetal cardiac structures, and one depicted clear information regarding the disposition and compression of the heart and lungs in diaphragmatic hernia. This study has shown the potential of 3D MR imaging in support of postmortem examination and for interactive visual teaching of the fetal cardiac structures. The new technique may eventually be of significance in prenatal detection of cardiac abnormalities with the development of fast real-time MR imaging.

Non-invasive perinatal necropsy by magnetic resonance imaging.

BACKGROUND: AT present necropsy is done in less than 60% of cases of perinatal death in the UK, despite the value of the procedure to the bereaved parents and their doctors. This low rate reflects the difficulty in discussing the examination during the acute distress after the death of a baby, and the personal and religious objections of many parents to necropsy. We compared post-mortem magnetic resonance imaging (MRI) of the fetus with internal perinatal necropsy to assess whether MRI examination is a feasible option for the 40% of cases where consent for necropsy is not given or requested. METHODS: We examined 20 stillborn, miscarried, or aborted fetuses by MRI and necropsy. Scanning was done in a 1.5 T system, in accordance with our protocol, immediately before necropsy. The MRI and necropsy findings were compared to assess how much diagnostic information was obtained by each technique. FINDINGS: In eight of the 20 cases the two examinations were in total agreement about the abnormalities present. In eight cases the necropsy provided more detailed information than MRI examination, but in four cases the MRI information was more extensive than that obtained at necropsy. In two of the latter cases, abnormalities of the central nervous system were seen only on MRI. Thus, in 12 (60%) of the 20 cases studied, MRI had equivalent or better diagnostic sensitivity than internal necropsy examination; in 18 (90%) of the 20 cases the two examinations were of similar clinical significance. INTERPRETATION: MRI of the stillborn or aborted fetus provides non-invasive access to information previously available only from necropsy.

Dynamic magnetic resonance mammography of both breasts following local excision and radiotherapy for breast carcinoma.

The purpose of this study was to evaluate a dynamic gadolinium-diethylene-triaminepentacetate (Gd-DTPA) enhanced magnetic resonance mammography (MRM) protocol, incorporating image subtraction and using a dedicated double breast coil, in patients with treated breast cancer. 36 patients who had undergone breast conserving surgery and radiotherapy, with clinical or mammographic suspicion of locally recurrent breast carcinoma, were examined. 3D rapid volume imaging of both breasts was performed before and repeated three times, at 1, 2 and 3 min, following Gd-DTPA enhancement. Image subtraction allowed identification of enhancing lesions and quantitative analysis of these was performed. Five patients had six lesions demonstrating rapid enhancement in the first minute, all of which were histologically confirmed recurrent or second primary tumours. Slower enhancement was seen in six benign lesions and diffuse enhancement was seen in one patient within 6 months of treatment. The dynamic protocol used allowed sufficient temporal resolution for distinguishing malignant from benign lesions at the site of previous surgery and ensured that both breasts were imaged in their entirety, thus enabling the diagnosis of multifocal and second primary tumours.

Measurement of spin-lattice relaxation times with FLASH for dynamic MRI of the breast.

Using a variable flip angle gradient refocused imaging technique, dynamic quantitative T1 relaxation maps acquired before and after the administration of a gadolinium contrast bolus enable the concentration-time curve of the paramagnetic agent in breast tissue to be calculated. This imaging technique has the aim of improving the diagnostic accuracy of MR mammography. Measurements with phantoms of calibrated T1 values have been carried out to investigate the accuracy of the method, with particular reference to errors caused by incomplete spoiling of residual transverse magnetization and inaccurate radio frequency (RF) flip-angle settings. A clinical example is presented. The method has potential use for any patient study which necessitates rapid quantitation of changing in vivo T1 values as a result of contrast agent injection.

Choice of contrast enhancement index for dynamic magnetic resonance mammography.

Indices are often used in dynamic MRI of the breast to quantitate signal enhancement within suspicious lesions. Two indices are commonly used: one calculates the difference in pre- and postcontrast signal intensity, normalised to a base-line signal intensity such as that of fat (which does not enhance) whilst the other calculates the ratio of pre- to postcontrast signal intensity. The results of a computational simulation are presented which demonstrate the superiority of the normalised signal difference index, based on the criterion that the best index is that which is least influenced by initial tissue T1. This hypothesis was tested by comparing the two indices in a group of patients with clinical or mammographic suspicion of recurrent breast carcinoma. Of 37 patient examinations using Gadolinium enhanced MRI of the breast, 11 patients showed 13 lesions with some degree of enhancement, which were subsequently diagnosed histologically as either benign or malignant. The normalised signal difference index showed no overlap between the benign and malignant groups, whereas some overlap was observed with the signal ratio index. The clinical findings are therefore consistent with the results of the computational simulation.