Precision of dual photon absorptiometry measurements: comparison of three different methods of selection of the region of interest

To determine the short-term reproducibility of bone mass calculations with dual photon absorptiometry of the lumbar spine (L2-L4), duplicate measurements in healthy subjects were used. Three different methods for selection of region of interest were compared: a rectangular region with variable height and width, an irregular region to be drawn freely by the operator and the standard calculation software supplied with the bone densitometer. Contributions of changes in size and location of the region of interest on calculated bone mineral mass were also investigated. An increase in height of the region by 2 scan lines caused an increase in bone mineral content (BMC) of 8.4% +/- 1.8%. Enlargement in width by 2 pixels in each scan line caused an increase in BMC of 2.5% +/- 1.3%. The difference between these region of interest changes was significant (P less than 0.0005). The use of a rectangular region, optimized to enclose L2-L4 in each person but of the same size in both measurements, resulted in a reproducibility of 1.4% and 0.7% respectively for 2 observers, with an inter observer variation of 1.2%. The reproducibility of the duplicate measurements was worse for the other methods of region of interest selection. A further series of duplicate DPA measurements in normal subjects, but with a standard meal between the measurements, showed a larger variation in the results. Again the reproducibility of the calculations using the rectangular region was better than with the other methods, with much less inter observer variation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Precision of dual photon absorptiometry measurements: comparison of three different methods of selection of the region of interest

To determine the short-term reproducibility of bone mass calculations with dual photon absorptiometry of the lumbar spine (L2–L4), duplicate measurements in healthy subjects were used. Three different methods for selection of region of interest were compared: a rectangular region with variable height and width, an irregular region to be drawn freely by the operator and the standard calculation software supplied with the bone densitometer. Contributions of changes in size and location of the region of interest on calculated bone mineral mass were also investigated. An increase in height of the region by 2 scan lines caused an increase in bone mineral content (BMC) of 8.4%±1.8%. Enlargement in width by 2 pixels in each scan line caused an increase in BMC of 2.5%±1.3%. The difference between these region of interest changes was significant (P0.0005). The use of a rectangular region, optimized to enclose L2–L4 in each person but of the same size in both measurements, resulted in a reproducibility of 1.4% and 0.7% respectively for 2 observers, with an inter observer variation of 1.2%. The reproducibility of the duplicate measurements was worse for the other methods of region of interest selection. A further series of duplicate DPA measurements in normal subjects, but with a standard meal between the measurements, showed a larger variation in the results. Again the reproducibility of the calculations using the rectangular region was better than with the other methods, with much less inter observer variation. These data suggest that calculation of dual photon absorptiometry results with a constant region of interest is preferred for the detection of small changes in lumbar bone mass.     

Single region of interest versus multislice T2* MRI approach for the quantification of hepatic iron overload

Purpose

To evaluate the effectiveness of the single ROI approach for the detection of hepatic iron burden in thalassemia major (TM) patients in respect to a whole liver measurement.

Materials and Methods

Five transverse hepatic slices were acquired by a T2* gradient‐echo sequence in 101 TM patients and 20 healthy subjects. The T2* value was calculated in a single region of interest (ROI) defined in the medium‐hepatic slice. Moreover, the T2* value was extracted on each of the eight ROIs defined in the functionally independent segments. The mean hepatic T2* value was calculated.

Results

For patients, the mean T2* values over segments VII and VIII were significantly lower. This pattern was substantially preserved in the two groups identified considering the T2* normal cutoff. All segmental T2* values were correlated with the single ROI T2* value. After the application of a correction map based on T2* fluctuations in the healthy subjects, no significant differences were found in the segmental T2* values.

Conclusion

Hepatic T2* variations are low and due to artifacts and measurement variability. The single ROI approach can be adopted in the clinical arena, taking care to avoid the susceptibility artifacts, occurring mainly in segments VII and VIII. J. Magn. Reson. Imaging 2011;33:348–355. © 2011 Wiley‐Liss, Inc.     

Multilattice sampling strategies for region of interest dynamic MRI

A multilattice sampling approach is proposed for dynamic MRI with Cartesian trajectories. It relies on the use of sampling patterns composed of several different lattices and exploits an image model where only some parts of the image are dynamic, whereas the rest is assumed static. Given the parameters of such an image model, the methodology followed for the design of a multilattice sampling pattern adapted to the model is described. The multi‐lattice approach is compared to single‐lattice sampling, as used by traditional acceleration methods such as UNFOLD (UNaliasing by Fourier‐Encoding the Overlaps using the temporal Dimension) or k‐t BLAST, and random sampling used by modern compressed sensing‐based methods. On the considered image model, it allows more flexibility and higher accelerations than lattice sampling and better performance than random sampling. The method is illustrated on a phase‐contrast carotid blood velocity mapping MR experiment. Combining the multilattice approach with the KEYHOLE technique allows up to 12× acceleration factors. Simulation and in vivo undersampling results validate the method. Compared to lattice and random sampling, multilattice sampling provides significant gains at high acceleration factors. Magn Reson Med 70:392–403, 2013. © 2012 Wiley Periodicals, Inc.     

The effect of region of interest selection on dual energy X-ray absorptiometry measurements of the calcaneus in 55 post-menopausal women

Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA) in four different regions of the calcaneus in 20 pre-menopausal and 55 post-menopausal women, none of whom were on treatment or suffering from conditions affecting bone. The total body option in the small animal software package of a Lunar DPX-L bone densitometer was used. The precision of the technique (%CV) varied from 0.7 to 2.2% depending on the region scanned. For post-menopausal women, BMD results in the mid and posterior parts of the calcaneus varied by < 7% while BMD in the anterior region was about 20% lower. DXA of the calcaneus was compared with measurements at the spine (L2-L4) and hip (femoral neck) and changes with age were estimated from cross-sectional data. BMD of the calcaneus was significantly reduced in 28 post-menopausal women with low lumbar spine BMD (-2SD) compared with women with normal spine BMD. Calcaneal BMD was significantly correlated to axial BMD (r = 0.45-0.77) and to age (r = 0.45 to -0.63). For a subgroup of 33 post-menopausal women measured twice after approximately 1 year, calcaneus BMD decreased by between 1.2% and 2.5% while axial BMD showed no significant change. Unlike spine or femoral neck BMD, the decrease in calcaneus BMD was significantly greater in women with low spine BMD than in normal women, possibly indicating improved detection of skeletal changes. The optimum measurement sites for BMD in the calcaneus were within the mid or posterior part of the calcaneus or enclosing the whole posterior calcaneus. The calcaneus was shown to be a precise, sensitive and simple measurement site suitable for the assessment of osteoporosis, especially in the elderly where degenerative changes in the spine and hip can complicate BMD assessment.     

MRI patient selection for endovascular thrombectomy in acute ischemic stroke: correlation between pretreatment diffusion weighted imaging and outcome scores

Introduction

Eligibility for endovascular treatment (EVT) in patients with acute ischemic stroke (AIS) depends, amongst other factors, on CT- or MR-based scores. The aim of this study was to investigate the role of Alberta Stroke Program Early CT score based on diffusion weighted imaging (MR-ASPECT) in the assessment of brain damage pre-EVT, patient selection for EVT and outcome.

Materials and methods

We included in this study patients with National Institute of Health stroke score (NIHSS) at admission?≥?8, MR-ASPECT?≥?5 and anterior AIS, who were treated with EVT in our hospital. All patients were clinically evaluated at admission, post-EVT, discharge and at 3-month follow-up. We used MR-ASPECT to establish infarct core extension at admission. We evaluated ASPECT score at admission (CT-ASPECT-IN), 24 h after EVT and at discharge, NIHSS, modified Ranking Scale (mRS), Thrombolysis in Cerebral Infarction scale (TICI), onset-to-intervention-delay (OTID) and Collateral Circulation Score (CCS).

Results

68 patients (mean age 78?±?11.9 years) were included in this study. 54.4 and 64.7% of patients had strong clinical improvement after 24 h from EVT and at discharge, respectively. NIHSS evaluated 24 h after EVT correlated with CCS, TICI and OTID. We observed a favourable outcome (mRS 0–2) in 52.9% of patients at 3-month follow-up. MR-ASPECT score correlated with post-EVT outcome better than CT-ASPECT-IN scores.

Conclusion

MR-ASPECT score based on diffusion weighted imaging is useful for the selection of patients with AIS that can have a favourable outcome from EVT. A prompt EVT has huge impact on patient outcome.

     

Effect of region of interest selection on first-pass radionuclide cardiac output determination

In principle, region of interest (ROI) selection should not affect the measurement of cardiac output by the first-pass technique with a radioactive intravascular indicator. Clinical application of the method requires that this theoretical hypothesis be tested. Sixty-eight left anterior oblique first-pass studies were acquired with a scintillation camera and computer using red blood cells labeled in vitro with 99mTc. Calculated mean cardiac output varied in the following order with respect to ROI: lung greater than right heart greater than left ventricle greater than whole heart (both ventricles) greater than aorta. Similar variations were observed in patients both with and without valvular regurgitation. Regions of interest over left ventricle or whole heart yielded the best correlations with cardiac output by thermodilution (r = 0.96, 0.95, respectively, n = 28) as well as the smallest interobserver variations (r = 0.994, 0.995, respectively, n = 33). First-pass studies with [99mTc]red blood cells labeled in vitro can yield accurate, reproducible determinations of cardiac output provided that the effect of ROI selection is recognized and that regions are properly selected.     

Effect of region of interest on interobserver variance in apparent diffusion coefficient measures

BACKGROUND AND PURPOSE: Apparent diffusion coefficient (ADC) values derived from diffusion-weighted MR imaging are useful measurements for assessment of cellular alterations in pathologic conditions of the brain. In this study, two radiologists independently quantitated ADCs and region-of interest sizes in prespecified locations of human brain to test interobserver ADC variance and the effect of varying ROI sizes on ADC differences. METHODS: Twenty-seven patients with normal MR findings underwent diffusion-weighted imaging (b value = 1000 s/mm(2)) on a 1.5-T system. Two radiologists independently placed two ROI areas of 22 +/- 5 mm(2) and 62 +/- 6 mm(2) (former area inside the latter area) at different sites of the brain (centrum semiovale, frontal white matter, nucleus caudatus, putamen, thalamus, substantia nigra, red nucleus, and pons) from trace images. Differences in ADC measurement obtained from each region of the brain for each radiologist and the size of each ROI were compared statistically. RESULTS: Mean ADC of prespecified areas of brain ranged between 0.673 and 0.818 mm(2)/s x10(-3). Interobserver variance was significant in some of the specified areas (centrum semiovale, frontal white matter, pons, substantia nigra, and red nucleus). Varying ROI sizes at the pons, substantia nigra, and red nucleus yielded statistically different ADC values. CONCLUSION: ADC values are found to be unreliable for use in assessing brain disease in some specified areas of the brain owing to interobserver variance and different ROI sizes.     

Contrast agent concentration measurements affecting quantification of bolus-tracking perfusion MRI.

Measurement of the concentration of the contrast agent using dynamic susceptibility contrast MRI relies on field inhomogeneities caused by the presence of the paramagnetic agent. The usual method for calculation of the concentration from dynamic T2*-weighted images is based on two key assumptions: 1) a linear relation between the change in R2* and the contrast agent concentration, and 2) a negligible effect on the MR signal due to concurrent T1 changes. In this study the effect of inaccuracies in these two assumptions on perfusion measurements was investigated using simulations and in vivo data. The results of the simulations provide a quantitative characterization of the magnitude of these effects for various experimental conditions (e.g., when a 1-sec TR is used with TE=20 ms, the T1 effects can introduce up to 40% cerebral blood flow underestimation depending on the flip angle). These findings can be used as a guide to estimate the errors in specific practical implementations, as well as to optimize the sequence parameters to minimize their effect. In summary, this study shows that the arterial input function measurement should be corrected for nonlinear R2* effects and that care should be taken in the study design to avoid introducing significant T1 effects in perfusion quantification.     

Computer aided analysis of breast MRI enhancement kinetics using mean shift c lustering and multifeature iterative region of interest selection

Purpose:

To evaluate automatic characterization of a breast MR lesion by its spatially coherent region of interest (ROI).

Materials and Methods:

The method delineated 247 enhancing lesions using Otsu thresholding after manually placing a sphere. Mean Shift Clustering subdivided each volume, based on features including pharmacokinetic parameters. An iteratively trained classifier to predict the most suspicious ROI (IsR) was used, to predict the malignancy likelihood of each lesion. Performance was evaluated using receiver operator characteristic (ROC) analysis, and compared with a previous prototype. IsR was compared with noniterative training. The effect of adding BI‐RADS? morphology (from a radiologist) to the classifier was investigated.

Results:

The area under the ROC curve (AUC) was 0.83 (95% confidence interval [CI] of 0.77–0.88), and was 0.75 (95%CI = 0.68–0.81; P = 0.029) without pharmacokinetic features. IsR performed better than conventional selection, based on one feature (AUC 0.75, 95%CI = 0.68–0.81; P = 0.035). With morphology, the AUC was 0.84 (95%CI = 0.78–0.88) versus 0.82 without (P = 0.40).

Conclusion:

Breast lesions can be characterized by their most suspicious, contiguous ROI using multi‐feature clustering and iterative training. Characterization was improved by including pharmacokinetic modeling, while in our experiments, including morphology did not improve characterization. J. Magn. Reson. Imaging 2012;36:1104–1112. © 2012 Wiley Periodicals, Inc.

     

Classification and quantification of neuronal fiber pathways using diffusion tensor MRI.

Quantitative characterization of neuronal fiber pathways in vivo is of significant neurological and clinical interest. Using the capability of MR diffusion tensor imaging to determine the local orientations of neuronal fibers, novel algorithms were developed to bundle neuronal fiber pathways reconstructed in vivo with diffusion tensor images and to quantify various physical and geometric properties of fiber bundles. The reliability of the algorithms was examined with reproducibility tests. Illustrative results show that consistent physical and geometric measurements of novel properties of neuronal tissue can be obtained, which offer considerable potential for the quantitative study of fiber pathways in vivo.     

Free water elimination and mapping from diffusion MRI

Relating brain tissue properties to diffusion tensor imaging (DTI) is limited when an image voxel contains partial volume of brain tissue with free water, such as cerebrospinal fluid or edema, rendering the DTI indices no longer useful for describing the underlying tissue properties. We propose here a method for separating diffusion properties of brain tissue from surrounding free water while mapping the free water volume. This is achieved by fitting a bi‐tensor model for which a mathematical framework is introduced to stabilize the fitting. Applying the method on datasets from a healthy subject and a patient with edema yielded corrected DTI indices and a more complete tract reconstruction that passed next to the ventricles and through the edema. We were able to segment the edema into areas according to the condition of the underlying tissue. In addition, the volume of free water is suggested as a new quantitative contrast of diffusion MRI. The findings suggest that free water is not limited to the borders of the brain parenchyma; it therefore contributes to the architecture surrounding neuronal bundles and may indicate specific anatomical processes. The analysis requires a conventional DTI acquisition and can be easily merged with existing DTI pipelines. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Evaluation in femoral neck fracture scintimetry: modes of region of interest selection and influence on results

Different sized ROIs within the femoral head and different modes of calculation were used in [99mTc]MDP scintimetry after femoral neck fracture. In preoperative scintimetry, correction for increased trochanteric uptake gave the best discrimination, whereas in postoperative scintimetry the direct ratio fractured/intact femoral head was superior. The change in ROI size had little influence.