The reliability of radiation dose display of a computed tomography scanner.

BACKGROUND: Internationally, the typical allowed difference between the measured radiation dose and dose reported by a computed tomography (CT) scanner is ±20 %. The objective is to describe a method in order to analyse this difference in a CT scanner in the Emergency Department of Kanta-Häme Central Hospital, and to calculate a correction factor for more comparable radiation dose values in further studies. METHODS: Ten intra-day radiation dose measurements were performed with undisturbed setting. Measurement reports on differences between measured and displayed dose were gathered from the vendor maintenance and supervising authority over a 12-year period. Additionally, two in-house measurements were made. A total of 18 datapoints were collected, with some differences in measurement settings. Data were also analysed against imaging parameters, ambient air pressure and time to identify trends or associations in the variation of the discrepancy. RESULTS: Measured doses were generally lower than displayed doses. Differences between displayed and measured doses varied between -3.46 and -0.10 %, with a mean of -1.26 % in the intra-day measurements, and between +4.65 and -17.3 %, with a mean of -7.53 % in the long-term data. There were no trends nor connections in the variations. CONCLUSION: Since the acceptable difference between the radiation dose display and the measured dose is relevant, the average difference for every CT scanner should be determined before radiation dose studies, especially when comparing multiple scanners.

Maintenance and manipulation in spatial working memory: dissociations in the prefrontal cortex.

Two experiments were conducted to compare thec ries of the functional organization of spatial working memory within the human prefrontal cortex. In Experiment I, memory set size for locations was parametrically varied, allowing for the assessment of BOLD signal across maintenance requirements. In the sec ond experiment, manipulation of spatial information held in working memory was contrasted with simple maintenance of that information. Both experiment evoked significant activity in a distributed spatia working memory network. Although dorsolateral prefrontal activation increased monotonically with memory set size, this region was differentially engaged in task conditions involving explicit manipulation of in ternal representations. Activation in the superior frontal sulcal region was associated with maintenance of spatial information, increasing with memory se size. In contrast, ventrolateral prefrontal activation was present only at the highest memory set size, possibly due to the differential use of organizational strategies with more complex stimuli. These results sup port claims that the dorsolateral prefrontal cortex is involved in the manipulation of internal representa tions and that the superior frontal sulcal region is involved in the maintenance of spatial information but they suggest a complex role for the ventrolatera prefrontal region.

Genetic influences on brain structure.

Here we report on detailed three-dimensional maps revealing how brain structure is influenced by individual genetic differences. A genetic continuum was detected in which brain structure was increasingly similar in subjects with increasing genetic affinity. Genetic factors significantly influenced cortical structure in Broca's and Wernicke's language areas, as well as frontal brain regions (r2(MZ) > 0.8, p < 0.05). Preliminary correlations were performed suggesting that frontal gray matter differences may be linked to Spearman's g, which measures successful test performance across multiple cognitive domains (p < 0.05). These genetic brain maps reveal how genes determine individual differences, and may shed light on the heritability of cognitive and linguistic skills, as well as genetic liability for diseases that affect the human cortex.

Pancreatic carcinoma and fast MR imaging: technical considerations for signal intensity difference measurements.

The aim of the study was to find the fast magnetic resonance imaging (MRI) sequence with the best conspicuity of pancreatic lesions at 1.0 T and 1.5 T. A total of 51 patients were studied. At 1.0 T, 22 patients with verified malignant pancreatic lesions were studied using the T1-weighted breath-hold spoiled Gradient Echo 2D FLASH(75) or FLASH(80) sequences, both non-enhanced and enhanced with gadolinium. The relative signal intensity difference (SIDR) between lesion and pancreas was measured. At 1.5 T, 20 patients with primary malignant lesions of the pancreas, and nine patients with 13 benign cystic lesions were examined with the breath-hold T2-weighted TrueFISP, HASTE, T1-weighted 2D FLASH(80) and FLASH(50) fat saturation sequences, the latter also enhanced. The signal intensity (SI) values of the pancreas and lesions as well as the pancreatic standard deviation (S.D.) were assessed, and the contrast-to-noise ratio (C/N) was determined. Statistical significances were calculated using an analysis of variance. No statistically significant difference between the sequences used in the conspicuity of cancer was found, either at 1.0 T or at 1.5 T. At 1.5 T, the T2-weighted TrueFISP and HASTE sequences could differentiate benign, cystic lesions from malignant lesions.

Fetal shoulder measurements by fast and ultrafast MRI techniques.

The purpose of this study was to evaluate magnetic resonance imaging (MRI) of fetal shoulder measurements of fetuses with suspected macrosomia. The actual fetal shoulder measurements made immediately after birth were compared with measurements obtained by fast and ultrafast MRI techniques antepartum. Eight singleton diabetic pregnant mothers underwent MRI examination with fast imaging in steady-state precession (TrueFISP) and spin-echo (SE) and gradient-echo (GE) echo-planar (EPI) sequences to show the fetal shoulder width. The actual shoulder width was measured immediately postpartum by a neonatologist. There was a statistically significant correlation between the MRI measurements and the actual shoulder width (P < 0.001 - P < 0.05) for all sequences. TrueFISP (r = 0.98, P < 0.001) was superior to EPI sequences (r = 0.88, P < 0.01 for SE EPI and r = 0.80, P < 0.05 for GE EPI). The images of all three sequences used were free of major motion artifacts. Fast and ultrafast sequences seem to be reliable for fetal shoulder measurements and the TrueFISP was the most accurate sequence compared to SE and GE echo-planar sequences. J. Magn. Reson. Imaging 2001;13:938-942.

Ultrasonography in the quantification of arterial involvement in Takayasu's arteritis.

OBJECTIVE: To evaluate the accuracy of ultrasonography (US) in the detection and quantification of arterial involvement in Takayasu's arteritis (TA). METHODS: The common carotid and subclavian arteries, and the abdominal aorta of 15 patients with TA were studied by Color Doppler (CD) US and Doppler spectral analysis and compared with angiography. RESULTS: The mean difference (+/-SD) between the percent luminal stenoses measured at angiography and by CD US was 2.0+/-10.3% for the common carotid artery, 4.0+/-23.6% for the subclavian artery and -1.3+/-16.8% for the abdominal aorta. The differences were not statistically significant. However, the agreement of the methods was less than satisfactory as shown by the wide standard deviations. CONCLUSIONS: More efforts are needed to improve the less than optimal agreement of US with angiography regarding the severity of individual stenoses. The technique performs best in the study of carotid arteries.

Detection of severe acute pancreatitis by contrast-enhanced magnetic resonance imaging.

The aim of the study was to assess the ability of MRI to differentiate between the two forms of severity of acute pancreatitis (AP), which is important for the detection of patients who require intensive monitoring and therapy. The second objective was to evaluate whether the distinction would be possible regardless of the MRI equipment. Magnetic resonance imaging was performed before and after intravenous administration of a gadolinium (Gd) chelate at 1.0 T using the breath-hold multislice rapid gradient-echo turbo fast low-angle shot (FLASH) sequence in 14 patients, and at 1.5 T with the 2D FLASH(50) sequence with fat saturation in 18 patients with acute pancreatitis early in the course of the disease. The patients were classified according to the Atlanta classification system as having the mild (MAP) or severe (SAP) form of the disease. At 1.0 T with use of a body coil, contrast-enhanced MRI failed to distinguish mild from severe pancreatitis. At 1.5 T with a phased-array body coil, the signal intensities of the patients with SAP were statistically significantly lower than those of the MAP group. Our initial clinical experience suggests that MRI with a sufficient magnetic field gradient strength may be useful for separating the two forms of acute pancreatitis in their early phases.

Transmission imaging for registration of ictal and interictal single-photon emission tomography, magnetic resonance imaging and electroencephalography.

A method developed for registration of ictal and interictal single-photon emission tomography (SPET), magnetic resonance imaging (MRI) and electroencephalography (EEG) is described. For SPET studies, technetium-99m ethyl cysteinate dimer (ECD) was injected intravenously while the patient was monitored on video-EEG to document the ictal or interictal state. Imaging was performed using a triple-head gamma camera equipped with a transmission imaging device using a gadolinium-153 source. The images (128x128 pixels, voxel size 3.7x3.7x3.6 mm3) were reconstructed using an iterative algorithm and postfiltered with a Wiener filter. The gold-plated silver electrodes on the patient's scalp were utilized as markers for registration of the ictal and interictal SPET images, as these metallic markers were clearly seen on the transmission images. Fitting of the marker sets was based on a non-iterative least squares method. The interictal SPET image was subtracted from the ictal image after scaling. The T1-weighted MPRAGE MR images with voxel size of 1.0x1.0x1.0 mm3 were obtained with a 1.5-T scanner. For registration of MR and subtraction SPET images, the external marker set of the ictal SPET study was fitted to the surface of the head segmented from MR images. The SPET registration was tested with a phantom experiment. Registration of ictal and interictal SPET in five patient studies resulted in a 2-mm RMS residual of the marker sets. The estimated RMS error of registration in the final result combining locations of the electrodes, subtraction SPET and MR images was 3-5 mm. In conclusion, transmission imaging can be utilized for an accurate and easily implemented registration procedure for ictal and interictal SPET, MRI and EEG.

Nonfluoroscopic localization of an amagnetic stimulation catheter by multichannel magnetocardiography.

This study was performed to: (1) evaluate the accuracy of noninvasive magnetocardiographic (MCG) localization of an amagnetic stimulation catheter; (2) validate the feasibility of this multipurpose catheter; and (3) study the characteristics of cardiac evoked fields. A stimulation catheter specially designed to produce no magnetic disturbances was inserted into the heart of five patients after routine electrophysiological studies. The catheter position was documented on biplane cine x-ray images. MCG signals were then recorded in a magnetically shielded room during cardiac pacing. Noninvasive localization of the catheter's tip and stimulated depolarization was computed from measured MCG data using a moving equivalent current-dipole source in patient-specific boundary element torso models. In all five patients, the MCG localizations were anatomically in good agreement with the catheter positions defined from the x-ray images. The mean distance between the position of the tip of the catheter defined from x-ray fluoroscopy and the MCG localization was 11 +/- 4 mm. The mean three-dimensional difference between the MCG localization at the peak stimulus and the MCG localization, during the ventricular evoked response about 3 ms later, was 4 +/- 1 mm calculated from signal-averaged data. The 95% confidence interval of beat-to-beat localization of the tip of the stimulation catheter from ten consecutive beats in the patients was 4 +/- 2 mm. The propagation velocity of the equivalent current dipole between 5 and 10 ms after the peak stimulus was 0.9 +/- 0.2 m/s. The results show that the use of the amagnetic catheter is technically feasible and reliable in clinical studies. The accurate three-dimensional localization of this multipurpose catheter by multichannel MCG suggests that the method could be developed toward a useful clinical tool during electrophysiological studies.

Regional gray matter, white matter, and cerebrospinal fluid distributions in schizophrenic patients, their siblings, and controls.

BACKGROUND: Cortical gray matter volume reductions and cerebrospinal fluid (CSF) volume increases are robust correlates of schizophrenia, but their sources have not been established conclusively. METHODS: Structured diagnostic interviews and magnetic resonance imaging scans of the brain were obtained on 75 psychotic probands (63 with schizophrenia and 12 with schizoaffective disorder), ascertained so as to be representative of all such probands in a Helsinki, Finland, birth cohort; 60 of their nonpsychotic full siblings; and 56 demographically similar control subjects without a personal or family history of treated psychiatric morbidity. RESULTS: Patients with schizophrenia and their siblings exhibited significant reductions in cortical gray matter volume and significant increases in sulcal CSF volume compared with controls. The patients, but not their siblings, also exhibited significant reductions in white matter volume and significant increases in ventricular CSF volume. Regional effects were most robust when component volumes were expressed as percentages of overall regional volumes; in this case, for patient and sibling groups, gray matter volume reductions and sulcal CSF volume increases were significantly more pronounced in the frontal and temporal lobes than in the remainder of the brain. None of the group differences varied significantly by sex or hemisphere. CONCLUSIONS: Structural alterations of the cerebral cortex, particularly in the frontal and temporal lobes, are present in patients with schizophrenia and in some of their siblings without schizophrenia; such changes are thus likely to reflect genetic (or shared environmental) effects. Ventricular enlargement is unique to the clinical phenotype and is thus likely to be affected primarily by nonshared causative factors.

MR gradient echo volumetric analysis of human cardiac casts: focus on the right ventricle.

PURPOSE: Our goal was to assess the utility of different imaging directions in volumetric studies of the heart with MRI, in particular to identify the optimal imaging plane for studies of the right ventricle. METHOD: We examined 12 sets of human four-chamber cadaveric cardiac casts. Gradient echo MRI was performed in four imaging planes: (a) perpendicular to the right ventricular inflow tract; (b) perpendicular to the right ventricular outflow tract; (c) in the left ventricular short axis view; and (d) in the axial view. The volumes of the right ventricle and other cardiac cavities were determined with the method of discs. The true cast volumes were measured with the water displacement technique. The agreement between true and measured volumes and the repeatability of image analysis were determined using the Bland-Altman method. RESULTS: There were no statistically significant differences between the measured and true right ventricular volumes irrespective of the imaging plane. The axial plane gave the smallest mean absolute difference from the true right ventricular volume (3.2 +/-2.2 ml) and also the best repeatability of volume analysis (0.2+/-1.6 ml). However, the other imaging planes performed nearly as well, and the differences across the planes were not statistically significant (p > 0.05). Also, in studies of the left ventricle and left and right atrium, the axial view appeared to give the best results, but differences across the imaging planes remained small. CONCLUSION: The present studies of human cardiac casts suggest that gradient echo MRI is well applicable to right ventricular volume measurements. Imaging the right ventricle in axial planes covering the entire heart gives good agreement with true right ventricular volumes and excellent analysis reproducibility. However, other imaging directions perform nearly as well, and thus selection of the imaging plane may not be of major importance to the accuracy of cardiac volume measurements with MR.

Multiphase segmented k-space velocity mapping in pulsatile flow waveforms.

The aim of the present study was to obtain the precision of flow measurement in breath-hold segmented k-space flow sequences. The results are based on studies of pulsatile flow in a phantom tube. The ultimate purpose is to use these sequences to measure coronary flow. In abdominal and cardiothoracic magnetic resonance imaging the image quality is degraded due to respiratory motion. In the segmented k-space acquisition method, one obtains many phase-encoding steps or views per cardiac phase. This shortens imaging time in the order of phase-encoding lines and makes it possible to image in a single breath-hold, thereby eliminating respiratory artefacts and improving edge detection. With breath-hold multiframe cine flow images it is possible to evaluate flow in all abdominal and cardiothoracic areas, including the coronary arteries. Our study shows that velocity curves shift in time when the number of k-space ky-lines per segment (LPS) are varied; this shift is linear as a function of LPS. The mean velocity Vmean in the center of mass of the pulsatile peak is constant (Vmean = 40.1 +/- 2.9 cm/s) and time t = -10.1 x LPS + 268 (r = 0.993, p < 0.0001). Correlation between theoretical and experimental flow curves is also linear as a function of LPS: C = -0.977 * LPS (r = 0.987, p < 0.0001). It is concluded that velocity curves move with LPS and are smoothed when the breath-hold velocity mapping is used. The more LPS is gathered the more inaccurate results are. LPS 7 or more cannot be considered clinically relevant.

Accuracy of a registration procedure for brain SPET and MRI: phantom and simulation studies.

Phantom experiments and simulations were performed to evaluate the significance of different error sources in a clinical registration procedure for brain SPET and MRI based on external markers. The results from the phantom experiments were used to adjust the error model for simulations. In the phantom experiments, 13-14 external markers were attached to the surface of a three-dimensional brain phantom for computing registration. Three internal test markers were used to estimate the accuracy of registration. The phantom was imaged with two different SPET and MRI devices. The mean root-mean-squared (RMS) residual of the locations of the test markers after registration using different combinations of four external markers varied from 3.5 +/- 1.0 to 5.2 +/- 1.3 mm depending on the imaging equipment and parameters used. The accuracy improved with an increasing number of external markers, from 3.2 +/- 0.5 to 4.9 +/- 0.5 mm for 6 markers and from 3.1 +/- 0.1 to 4.7 +/- 0.1 mm for 13 markers. In simulations, the external markers had an error comparable to the corresponding error in the phantom experiments. The error in the test markers was varied independently of that of the external markers. When the locating error of the test markers was removed, about 2 mm of the residuals of the test markers were found to come from this source. When an error comparable to the resolution of the original images (7-10 mm for SPET, 2 mm for MRI) was included in the test markers, the largest mean RMS residual after registration was smaller than the resolution error (8.8 +/- 1.1 mm). This was due to the accuracy of localization of the external markers and the fact that the direction of the error was random for each marker. The size of the registration error of an image volume was site-dependent, being minimal near the centre of mass of the external markers. When comparing the error with the spatial resolution of SPET, it was concluded that the accuracy of registration is not the limiting factor in region-of-interest analysis of registered images, provided that the design and attachment of the marker system are appropriate.

MRI of neuronal ceroid lipofuscinosis. II. Postmortem MRI and histopathological study of the brain in 16 cases of neuronal ceroid lipofuscinosis of juvenile or late infantile type.

Postmortem MRI was carried out on the formalin-fixed brains of 14 patients with juvenile (JNCL) and two with late infantile neuronal ceroid lipofuscinosis, one of variant and the other of classical type. Two patients with JNCL had also undergone MRI during life. After MRI, specimens for histopathological analysis were taken from standard areas of the cerebral cortex, deep nuclei and white matter. The signal intensity of the periventricular white matter was usually higher than that of the peripheral white matter, a finding which correlated with the severe periventricular loss of myelin and gliosis observed histologically. The signal intensity was usually lower in the thalamus than in the putamen; in some patients the signal intensity of the thalamus was equal to or even lower than that of the white matter. However, myelin loss, gliosis, the storage process or neuronal loss in the thalamus did not correlate with the MRI findings. Since in one patient with JNCL the ante- and postmortem MRI did not differ basically, it appears probable that the periventricular changes detected in vivo on MRI are due to the severe loss of myelin and gliosis observed in this study. However, changes resulting from the fixation process must be considered, when postmortem and in vivo MRI are correlated.

Contrast-enhanced magnetic resonance imaging for the detection of acute haemorrhagic necrotizing pancreatitis.

Eleven piglets with haemorrhagic necrotizing pancreatitis and nine piglets with oedematous pancreatitis were imaged using a multi-breath-hold TurboFLASH (TR 6.5 ms, TE 3 ms, TI 300 ms, flip angle 8 degrees , three slices) pre-excited T1-weighted sequence with an IV bolus injection of gadopentetate dimeglumine (Gd-DTPA, 0. 3 mmol/kg) as a contrast agent to show dynamic contrast enhancement of the pancreas by MRI. All piglets were imaged according to the same protocol before inducing the disease. Following the IV Gd-DTPA bolus, time-enhancement curve of the pancreas during haemorrhagic necrotizing pancreatitis was significantly lower than during oedematous pancreatitis. The enhancement curves for the healthy piglets and piglets with oedematous pancreatitis did not differ significantly. Each piglet served as its own control. Because the results of this initial study are similar to those obtained with contrast-enhanced CT, we conclude that our results may encourage further clinical trials, and contrast-enhanced dynamic MRI may be an alternative to the established method of CT for diagnosing acute haemorrhagic necrotizing pancreatitis.

Abdominal SPECT/MRI fusion applied to the study of splenic and hepatic uptake of radiolabeled thrombocytes and colloids.

The importance of applying MRI (CT)/SPECT fusion in the abdominal and thoracic areas has been recognized in recent studies aiming at radionuclide therapy of cancer. According to our earlier results spleen and liver volume determination with different segmentation methods is inaccurate with SPECT alone. We therefore applied a SPECT/MRI registration procedure to the estimation of spleen and liver volumes and spleen/liver activity ratios in three male volunteers administered 111In-labeled thrombocytes and 99mTc-labeled colloids. The objectives of the study were to investigate if the uptake of thrombocytes in the spleen and liver can be measured more accurately when the anatomical borders of these organs are transferred from MRI to SPECT, and to test a SPECT/MRI registration method for improving three-dimensional dosimetry for radiotherapy treatment planning. A good correlation was found between spleen/liver activity ratios calculated from volumetric average activity per pixel values and from total volumetric counts derived from registered data but not from projection data. The average registration residual with this SPECT/MRI fusion method is approximately 1-2 cm in the abdominal area. Combining anatomical images with SPECT is therefore important for improving quantitative SPECT also in the abdomen.

Arterial wall thickness measurements by B mode ultrasonography in patients with Takayasu's arteritis.

OBJECTIVE: To assess the feasibility and potential diagnostic usefulness of arterial ultrasonography in Takayasu's arteritis. METHODS: The total wall, intimal + medial, and adventitial thickness of the common carotid, subclavian and common femoral arteries, and of the abdominal aorta, were examined by B mode ultrasonography in 16 patients with Takayasu's arteritis and 16 healthy control subjects. RESULTS: The mean total wall and intimal + medial thickness of all arteries other than the common femoral were significantly increased in Takayasu's arteritis. Long segments of homogeneous circumferential wall thickening in multiple vessels were characteristic. When the common carotid and subclavian arteries and the abdominal aorta were examined, each individual with Takayasu's arteritis had at least one artery with total wall thickness exceeding the reference range in controls. CONCLUSIONS: B mode ultrasonography is able to expose the widespread arterial wall thickening characteristic of Takayasu's arteritis and may provide a useful tool for the detection and follow up of this disease.

Right and left atrial phasic volumetric function in mildly symptomatic dilated and hypertrophic cardiomyopathy: cine MR imaging assessment.

PURPOSE: To characterize biatrial phasic volumetric function in dilated and hypertrophic cardiomyopathy with cine magnetic resonance (MR) imaging. MATERIALS AND METHODS: Eight patients with dilated cardiomyopathy (mean age, 47 years), eight with hypertrophic cardiomyopathy (mean age, 39 years), and eight healthy subjects (mean age, 41 years) underwent cardiac-gated long-axis cine MR imaging of both atria. RESULTS: Left atrial minimum volume averaged 94 mL +/- 37 (standard deviation) in dilated cardiomyopathy, 86 mL +/- 40 in hypertrophic cardiomyopathy, and 51 mL +/- 14 in control subjects (P = .04). Left atrial ejection fraction averaged 16% +/- 6 in dilated cardiomyopathy, 19% +/- 12 in hypertrophic cardiomyopathy, and 28% +/- 7 in control subjects (P = .03). Right atrial minimum volume and ejection fraction were not altered in either form of cardiomyopathy. The normalized filling and emptying rates of either atrium were decreased in both forms of cardiomyopathy. CONCLUSION: In mildly symptomatic dilated and hypertrophic cardiomyopathy, and left atrium is enlarged and its relative cyclic volume changes are reduced. The right atrium is of normal size, but its reservoir function is compromised particularly in dilated cardiomyopathy. Three-dimensional volume measurements with cine MR imaging enable the exposure of altered atrial volumetric function.

A simplified method for the determination of left atrial size and function using cine magnetic resonance imaging.

This work aimed at developing a rapid and clinically applicable method for the assessment of left atrial size and function using magnetic resonance imaging (MRI). We studied 17 healthy subjects and 26 cardiac patients. Left atrial cine MRI with 50 ms phases was made in 6-12 contiguous long-axis sections encompassing the entire atrial cavity. A volume-time curve was reconstructed to measure the minimum and maximum volumes as well as the fractional volume change, reservoir function, ejection fraction, and mean filling and emptying rates of the left atrium. The image section with the largest left atrial area was then selected and a comparable area-time curve was reconstructed. The atrial phasic areas and functional indices were determined analogously to the volume-based assessment. The contours of atrial area-time and volume-time curves agreed closely in individual subjects. All area-based left atrial measurements distinguished cardiac patients as a group from healthy persons. The combined specificity of the area-based analyses was 92% and the sensitivity, 65%, in identifying abnormal results in individual patients. The accuracy of the area-based data was best for the atrial minimum size, fractional change, reservoir function, and mean filling rate. The estimated time savings with the simplified method were 5 to 6 h per patient. Left atrial size and function can be studied by reconstructing a phasic atrial area-time curve with cine MRI. Atrial enlargement and abnormalities of filling and reservoir function can be reliably identified, but if data on conduit or stroke function are crucial the three-dimensional MRI technique is still recommended.