OBJECTIVESThe aim of this study was to propose a magnetic resonance imaging acquisition and analysis protocol that uses image segmentation to measure and depict fluid, fat, and muscle volumes in ...breast cancer–related lymphoedema (BCRL). This study also aims to compare affected and control (unaffected) arms of patients with diagnosed BCRL, providing an analysis of both the volume and the distribution of the different tissue components.
MATERIALS AND METHODSThe entire arm was imaged with a fluid-sensitive STIR and a 2-point 3-dimensional T1W gradient-echo–based Dixon sequences, acquired in sagittal orientation and covering the same imaging volume. An automated image postprocessing procedure was developed to simultaneously (1) contour the external volume of the arm and the muscle fascia, allowing separation of the epifacial and subfascial volumes; and to (2) separate the voxels belonging to the muscle, fat, and fluid components. The total, subfascial, epifascial, muscle (subfascial), fluid (epifascial), and fat (epifascial) volumes were measured in 13 patients with unilateral BCRL. Affected versus unaffected volumes were compared using a 2-tailed paired t test; a value of P < 0.05 was considered to be significant. Pearson correlation was used to investigate the linear relationship between fat and fluid excess volumes. The distribution of fluid, fat, and epifascial excess volumes (affected minus unaffected) along the arm was also evaluated using dedicated tissue composition maps.
RESULTSTotal arm, epifascial, epifascial fluid, and epifascial fat volumes were significantly different (P < 0.0005), with greater volume in the affected arms. The increase in epifascial volume (globally, 94% of the excess volume) constituted the bulk of the lymphoedematous swelling, with fat comprising the main component. The total fat excess volume summed over all patients was 2.1 times that of fluid. Furthermore, fat and fluid excess volumes were linearly correlated (Pearson r = 0.75), with the fat excess volume being greater than the fluid in 11 subjects. Differences in muscle compartment volume between affected and unaffected arms were not statistically significant, and contributed only 6% to the total excess volume. Considering the distribution of the different tissue excess volumes, fluid accumulated prevalently around the elbow, with substantial involvement of the upper arm in only 3 cases. Fat excess volume was generally greater in the upper arm; however, the relative increase in epifascial volume, which considers the total swelling relative to the original size of the arm, was in 9 cases maximal within the forearm.
CONCLUSIONSOur measurements indicate that excess of fat within the epifascial layer was the main contributor to the swelling, even when a substantial accumulation of fluid was present. The proposed approach could be used to monitor how the internal components of BCRL evolve after presentation, to stratify patients for treatment, and to objectively assess treatment response. This methodology provides quantitative metrics not currently available during the standard clinical assessment of BCRL and shows potential for implementation in clinical practice.
MRI has been extensively used in breast cancer staging, management and high risk screening. Detection sensitivity is paramount in breast screening, but variations of signal-to-noise ratio (SNR) as a ...function of position are often overlooked. We propose and demonstrate practical methods to assess spatial SNR variations in dynamic contrast-enhanced (DCE) breast examinations and apply those methods to different protocols and systems. Four different protocols in three different MRI systems (1.5 and 3.0 T) with receiver coils of different design were employed on oil-filled test objects with and without uniformity filters. Twenty 3D datasets were acquired with each protocol; each dataset was acquired in under 60 s, thus complying with current breast DCE guidelines. In addition to the standard SNR calculated on a pixel-by-pixel basis, we propose other regional indices considering the mean and standard deviation of the signal over a small sub-region centred on each pixel. These regional indices include effects of the spatial variation of coil sensitivity and other structured artefacts. The proposed regional SNR indices demonstrate spatial variations in SNR as well as the presence of artefacts and sensitivity variations, which are otherwise difficult to quantify and might be overlooked in a clinical setting. Spatial variations in SNR depend on protocol choice and hardware characteristics. The use of uniformity filters was shown to lead to a rise of SNR values, altering the noise distribution. Correlation between noise in adjacent pixels was associated with data truncation along the phase encoding direction. Methods to characterise spatial SNR variations using regional information were demonstrated, with implications for quality assurance in breast screening and multi-centre trials.
Baseline T2* relaxation time has been proposed as an imaging biomarker in cancer, in addition to Dynamic Contrast-Enhanced (DCE) MRI and diffusion-weighted imaging (DWI) parameters. The purpose of ...the current work is to investigate sources of error in T2* measurements and the relationship between T2* and DCE and DWI functional parameters in breast cancer.
Five female volunteers and thirty-two women with biopsy proven breast cancer were scanned at 3 T, with Research Ethics Committee approval. T2* values of the normal breast were acquired from high-resolution, low-resolution and fat-suppressed gradient-echo sequences in volunteers, and compared. In breast cancer patients, pre-treatment T2*, DCE MRI and DWI were performed at baseline. Pathologically complete responders at surgery and non-responders were identified and compared. Principal component analysis (PCA) and cluster analysis (CA) were performed.
There were no significant differences between T2* values from high-resolution, low-resolution and fat-suppressed datasets (p > 0.05). There were not significant differences between baseline functional parameters in responders and non-responders (p > 0.05). However, there were differences in the relationship between T2* and contrast-agent uptake in responders and non-responders. Voxels of similar characteristics were grouped in 5 clusters, and large intra-tumoural variations of all parameters were demonstrated.
Breast T2* measurements at 3 T are robust, but spatial resolution should be carefully considered. T2* of breast tumours at baseline is unrelated to DCE and DWI parameters and contribute towards describing functional heterogeneity of breast tumours.
High grade and metastatic brain tumours exhibit considerable spatial variations in proliferation, angiogenesis, invasion, necrosis and oedema. Vascular heterogeneity arising from vascular co‐option ...in regions of invasive growth (in which the blood–brain barrier remains intact) and neoangiogenesis is a major challenge faced in the assessment of brain tumours by conventional MRI.
A multiparametric MRI approach, incorporating native measurements and both Gd‐DTPA (Magnevist) and ultrasmall superparamagnetic iron oxide (P904)‐enhanced imaging, was used in combination with histogram and unsupervised cluster analysis using a k‐means algorithm to examine the spatial distribution of vascular parameters, water diffusion characteristics and invasion in intracranially propagated rat RG2 gliomas and human MDA‐MB‐231 LM2–4 breast adenocarcinomas in mice.
Both tumour models presented with higher ΔR1 (the change in transverse relaxation rate R1 induced by Gd‐DTPA), fractional blood volume (fBV) and apparent diffusion coefficient than uninvolved regions of the brain. MDA‐MB‐231 LM2–4 tumours were less densely cellular than RG2 tumours and exhibited substantial local invasion, associated with oedema, whereas invasion in RG2 tumours was minimal. These additional features were reflected in the more heterogeneous appearance of MDA‐MB‐231 LM2–4 tumours on T2‐weighted images and maps of functional MRI parameters.
Unsupervised cluster analysis separated subregions with distinct functional properties; areas with a low fBV and relatively impermeable blood vessels (low ΔR1) were predominantly located at the tumour margins, regions of MDA‐MB‐231 LM2–4 tumours with relatively high levels of water diffusion and low vascular permeability and/or fBV corresponded to histologically identified regions of invasion and oedema, and areas of mismatch between vascular permeability and blood volume were identified.
We demonstrate that dual contrast MRI and evaluation of tissue diffusion properties, coupled with cluster analysis, allows for the assessment of heterogeneity within invasive brain tumours and the designation of functionally diverse subregions that may provide more informative predictive biomarkers.
Multiparametric MRI incorporating Gd‐DTPA and USPIO‐enhanced and diffusion‐weighted MRI was performed in intracranial RG2 and MDA‐MB‐231 LM2‐4 xenografts in mice. Unsupervised cluster analysis of calculated MRI parameters allowed for assessment of the patency of tumour vasculature by simultaneous assessment of vascular permeability and tumour blood volume, potentially allowing delineation of vasculogenic regions and regions of co‐opted brain vasculature. Spatial assessment of tissue diffusion properties in combination with vascular characteristics enabled the relationship between oedema and invasion/vascular co‐option to be evaluated.
Abstract Background When induction chemotherapy (IC) is used prior to chemoradiotherapy (CRT) in head and neck cancer (HNC), functional imaging (FI) may inform adaptation of treatment plans with the ...aim of optimising outcomes. Understanding the impact of IC on FI parameters is, therefore, essential. Purpose To prospectively evaluate the feasibility of acquiring serial FI (18 F-FDG-PET, diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) MRI) and its role in defining individualised treatment regimens following IC in HNC. Methods and materials Ten patients with stage III and IV HNC underwent conventional (CT and MRI) and functional (DW, DCE-MRI and18 F-FDG-PET/CT) imaging at baseline and following two cycles of IC prior to definitive CRT. Results One patient withdrew due to claustrophobia. Seven out of nine patients had a complete metabolic response to IC on18 F-FDG-PET imaging. DCE-MRI showed a significant fall in transfer constant (Ktrans ) (0.209 vs 0.129 min−1 P < 0.01) and integrated area under gadolinium curve at 60 s (IAUGC6O) (18.4 vs 11.9 mmol/min, P < 0.01) and DW-MRI a rise in ADC (0.89 vs 1.06 × 10−3 mm2 /s, P < 0.01) following IC. Conclusions Acquiring FI sequences is feasible in HNC. There are marked changes in FI parameters following IC which may guide adaptation of individualised treatment regimens.
Purpose:
To investigate the effects of different time-resolved angiography with stochastic trajectories (TWIST) k-space undersampling schemes on calculated pharmacokinetic dynamic contrast-enhanced ...(DCE) vascular parameters.
Methods:
A digital perfusion phantom was employed to simulate effects of TWIST on characteristics of signal changes in DCE. Furthermore, DCE-MRI was acquired without undersampling in a group of patients with head and neck squamous cell carcinoma and used to simulate a range of TWIST schemes. Errors were calculated as differences between reference and TWIST-simulated DCE parameters. Parametrical error maps were used to display the averaged results from all tumors.
Results:
For a relatively wide range of undersampling schemes, errors in pharmacokinetic parameters due to TWIST were under 10% for the volume transfer constant, K
trans, and total extracellular extravascular space volume, Ve
. TWIST induced errors in the total blood plasma volume, Vp
, were the largest observed, and these were inversely dependent on the area of the fully sampled k-space. The magnitudes of errors were not correlated with K
trans, Vp
and weakly correlated with Ve
.
Conclusions:
The authors demonstrated methods to validate and optimize k-space view-sharing techniques for pharmacokinetic DCE studies using a range of clinically relevant spatial and temporal patient derived data. The authors found a range of undersampling patterns for which the TWIST sequence can be reliably used in pharmacokinetic DCE-MRI. The parameter maps created in the study can help to make a decision between temporal and spatial resolution demands and the quality of enhancement curve characterization.
Contrast-Enhanced Magnetic Resonance Lymphangiography (CE-MRL) presents some limitations: (i) it does not quantify lymphatic functionality; and (ii) enhancement of vascular structures may confound ...image interpretation. Furthermore, although CE-MRL is well described in the published literature for the lower limbs, there is a paucity of data with regards to its use in the upper limbs. In this proof-of-principle study, we propose a new protocol to perform CE-MRL in the upper limbs of patients with breast cancer-related lymphedema (BCRL) which addresses these limitations.
CE-MRL was performed using a previously published (morphological) protocol and the proposed protocol (quantitative) on both the ipsilateral (abnormal) and contralateral (normal) arms of patients with BCRL. The quantitative protocol employs contrast agent (CA) intradermal injections at a lower concentration to prevent T2*-related signal decay. Both protocols provided high-resolution three-dimensional images of upper limb lymphatic vessels. CA uptake curves were utilized to distinguish between lymphatic vessels and vascular structures. The quantitative protocol minimized venous enhancement and avoided spurious delays in lymphatic enhancement due to short T2* values, enabling correct CA uptake characterization. The quantitative protocol was therefore employed to measure the lymphatic fluid velocity, which demonstrated functional differences between abnormal and normal arms. The velocity values were in agreement with previously reported lymphoscintigraphy and near infra-red lymphangiography measurements.
This work demonstrated the feasibility of CE-MRL of the upper limbs in patients with BRCL, introducing an advanced imaging and analysis protocol suitable for anatomical and functional study of the lymphatic system.
Integrating finite rotations Bottasso, Carlo L.; Borri, Marco
Computer methods in applied mechanics and engineering,
10/1998, Letnik:
164, Številka:
3
Journal Article
Recenzirano
We study the integration of problems of evolution in the rotation group. Instead of attacking the problem in the nonlinear differential manifold SO(3) (pure rotational dynamics), as is usually done, ...we derive equations for the complete problem of motion (translational and rotational dynamics) on an extended manifold. We develop a generalization of Runge-Kutta methods that, by design, ensures that the solution will remain on the manifold for any choice of the tableau. This is obtained through configuration updates performed via the exponential map. We show how certain terms can be approximated, while retaining the order of accuracy of the scheme, and how the method conserves the total momentum of the system. Within this framework, we develop two nonlinearly unconditionally stable time integration schemes, that are associated with discrete laws of conservation/dissipation of the total energy. The dissipating algorithm generalizes to the nonlinear case the high frequency damping characteristics provided by some well-known conventional methods. We present numerical results to support our analysis, and we develop a complete application of this methodology to the nonlinear dynamics of three-dimensional rods undergoing large displacements and finite rotations, under the assumption of small strains.
This work presents a novel methodology for the dynamic analysis of general non-linear multibody systems composed of rigid and deformable bodies, the latter under the small strain assumption. In Part ...I we developed the 6-D compact representation and parameterization of motion for constrained bodies. Part II is devoted to the design of a class of modified Runge–Kutta (RK) methods dedicated to non-linear dynamics. These are capable of integrating on the configuration manifold and of preserving linear and angular momenta. Within this class of methods, two second-order algorithms are designed under the requirement of attaining non-linear unconditional stability: the energy preserving (EP) and energy decaying (ED) methods. These schemes are associated with an algorithmic law of conservation and dissipation, respectively, of the total mechanical energy of the system, together with the vanishing of the algorithmic work done by ideal, time-independent constraints. Their performances are assessed with the aid of some representative numerical applications which confirm the non-conventional properties predicted in the analysis.
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