To evaluate sources of error in the Magnetic Resonance Imaging (MRI) measurement of percent fibroglandular tissue (%FGT) using two-point Dixon sequences for fat-water separation.
Ten female ...volunteers (median age: 31 yrs, range: 23-50 yrs) gave informed consent following Research Ethics Committee approval. Each volunteer was scanned twice following repositioning to enable an estimation of measurement repeatability from high-resolution gradient-echo (GRE) proton-density (PD)-weighted Dixon sequences. Differences in measures of %FGT attributable to resolution, T1 weighting and sequence type were assessed by comparison of this Dixon sequence with low-resolution GRE PD-weighted Dixon data, and against gradient-echo (GRE) or spin-echo (SE) based T1-weighted Dixon datasets, respectively.
%FGT measurement from high-resolution PD-weighted Dixon sequences had a coefficient of repeatability of ±4.3%. There was no significant difference in %FGT between high-resolution and low-resolution PD-weighted data. Values of %FGT from GRE and SE T1-weighted data were strongly correlated with that derived from PD-weighted data (r = 0.995 and 0.96, respectively). However, both sequences exhibited higher mean %FGT by 2.9% (p < 0.0001) and 12.6% (p < 0.0001), respectively, in comparison with PD-weighted data; the increase in %FGT from the SE T1-weighted sequence was significantly larger at lower breast densities.
Although measurement of %FGT at low resolution is feasible, T1 weighting and sequence type impact on the accuracy of Dixon-based %FGT measurements; Dixon MRI protocols for %FGT measurement should be carefully considered, particularly for longitudinal or multi-centre studies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Purpose:
Stringent quality assurance is required in MRI breast screening to ensure that different scanners and imaging protocols reach similar diagnostic performance. The authors propose a ...methodology, based on power spectrum analysis (PSA), to evaluate spatial resolution in clinical images. To demonstrate this approach, the authors have retrospectively compared two MRI sequences commonly employed in breast screening.
Methods:
In a novel approach to PSA, spatial frequency response curves (SFRCs) were extracted from the images. The SFRC characterizes spatial resolution describing the spatial frequency content of an image over a range of frequencies. Verification of the SFRCs was performed on MRI images of Eurospin agarose gel tubes acquired with different resolution settings. SFRCs of volunteer and patient images obtained with two clinical MRI sequences were then compared. The two sequences differed primarily in k-space coverage pattern, which was either radial (RAD) or linear (LIN).
Results:
The computed SFRCs were able to demonstrate the differences between RAD and LIN sequences in relatively small groups of subjects. The curves showed a similar pattern of decay in both volunteer and patient images, indicating that the spatial frequency response is mainly determined by the imaging protocol and not by intersubject anatomical differences. The LIN protocol produced images with increased sharpness; this was reflected in the corresponding SFRCs, which showed a higher content of spatial frequencies associated with image details.
Conclusions:
The SFRC can provide an objective assessment of the presence of spatial details in the image and represent a useful quality assurance tool in the evaluation of different breast screening protocols. With a reference image, a comparative analysis of the SFRCs could ensure that equivalent image quality is achieved across different scanners and sites.
To characterize the voxel-wise uncertainties of Apparent Diffusion Coefficient (ADC) estimation from whole-body diffusion-weighted imaging (WBDWI). This enables the calculation of a new parametric ...map based on estimates of ADC and ADC uncertainty to improve WBDWI imaging standardization and interpretation: NoIse-Corrected Exponentially-weighted diffusion-weighted MRI (niceDWI).
Three approaches to the joint modeling of voxel-wise ADC and ADC uncertainty (σ
) are evaluated: (i) direct weighted least squares (DWLS), (ii) iterative linear-weighted least-squares (IWLS), and (iii) smoothed IWLS (SIWLS). The statistical properties of these approaches in terms of ADC/σ
accuracy and precision is compared using Monte Carlo simulations. Our proposed post-processing methodology (niceDWI) is evaluated using an ice-water phantom, by comparing the contrast-to-noise ratio (CNR) with conventional exponentially-weighted DWI. We present the clinical feasibility of niceDWI in a pilot cohort of 16 patients with metastatic prostate cancer.
The statistical properties of ADC and σ
conformed closely to the theoretical predictions for DWLS, IWLS, and SIWLS fitting routines (a minor bias in parameter estimation is observed with DWLS). Ice-water phantom experiments demonstrated that a range of CNR could be generated using the niceDWI approach, and could improve CNR compared to conventional methods. We successfully implemented the niceDWI technique in our patient cohort, which visually improved the in-plane bias field compared with conventional WBDWI.
Measurement of the statistical uncertainty in ADC estimation provides a practical way to standardize WBDWI across different scanners, by providing quantitative image signals that improve its reliability. Our proposed method can overcome inter-scanner and intra-scanner WBDWI signal variations that can confound image interpretation.
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.
To compare tumor bed (TB) volumes delineated using magnetic resonance imaging plus computed tomography and clips (MRCT) with those delineated using CT and clips (CT/clips) alone in postlumpectomy ...breast cancer patients positioned prone and to determine the value of MRCT for planning partial breast irradiation (PBI).
Thirty women with breast cancer each had 6 to 12 titanium clips secured in the excision cavity walls at lumpectomy. Patients underwent CT imaging in the prone position, followed by MRI (T(1)-weighted standard and fat-suppressed and T(2)-weighted sequences) in the prone position. TB volumes were delineated separately on CT and on fused MRCT datasets. Clinical target volumes (CTV) (where CTV = TB + 15 mm) and planning target volumes (PTV) (where PTV = CTV + 10 mm) were generated. Conformity indices between CT- and MRCT-defined target volumes were calculated (ratio of the volume of agreement to total delineated volume). Discordance was expressed as a geographical miss index (GMI) (where the GMI = the fraction of total delineated volume not defined by CT) and a normal tissue index (the fraction of total delineated volume designated as normal tissue on MRCT). PBI dose distributions were generated to cover CT-defined CTV (CTV(CT)) with >or=95% of the reference dose. The percentage of MRCT-defined CTV (CTV(MRCT)) receiving >or=95% of the reference dose was measured.
Mean conformity indices were 0.54 (TB), 0.84 (CTV), and 0.89 (PTV). For TB volumes, the GMI was 0.37, and the NTI was 0.09. Median percentage volume coverage of CTV(CT) was 97.1% (range, 95.3%-100.0%) and of CTV(MRCT) was 96.5% (range, 89.0%-100.0%).
Addition of MR to CT/clip data generated TB volumes that were discordant with those based on CT/clips alone. However, clinically satisfactory coverage of CTV(MRCT) by CTV(CT)-based tangential PBI fields provides support for CT/clip-based TB delineation remaining the method of choice for PBI/breast boost radiotherapy planned using tangential fields.
To retrospectively investigate the effect of flip angle (FA) and k-space sampling on the performance of dynamic contrast-enhanced (DCE-) magnetic resonance imaging (MRI) breast sequences.
Five ...DCE-MRI breast sequences were evaluated (10°, 14°, and 18° FAs; radial or linear k-space sampling), with 7–10 patients in each group (n = 45). All sequences were compliant with current technical breast screening guidelines. Contrast agent (CA) uptake curves were constructed from the right mammary artery for each examination. Maximum relative enhancement, Emax, and time-to-peak enhancement, Tmax, were measured and compared between protocols (analysis of variance and Mann–Whitney). For each sequence, calculated values of maximum relative enhancement, Ecalc, were derived from the Bloch equations and compared to Emax. Fat suppression performance (residual bright fat and chemical shift artifact) was rated for each examination and compared between sequences (Fisher exact tests).
Significant differences were identified between DCE-MRI sequences. Emax increased significantly at higher FAs and with linear k-space sampling (P < .0001; P = .001). Radial protocols exhibited greater Tmax than linear protocols at FAs of both 14° (P = .025) and 18° (P < .0001), suggesting artificially flattened uptake curves. Good correlation was observed between Ecalc and Emax (r = 0.86). Fat suppression failure was more pronounced at an FA of 18° (P = .008).
This retrospective approach is validated as a tool to compare and optimize breast DCE-MRI sequences. Alterations in FA and k-space sampling result in significant differences in CA uptake curve shape which could potentially affect diagnostic interpretation. These results emphasize the need for careful parameter selection and greater standardization of breast DCE-MRI sequences.
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.
Magnetic resonance (MR) imaging and MR cholangiopancreatography are useful, noninvasive techniques for the assessment of pancreatic and hepatobiliary complications in cystic fibrosis. Abnormalities ...of the pancreas in cystic fibrosis are typically characterized by fat deposition, which has increased signal intensity on T1-weighted MR images, and pancreatic fibrosis, which has low signal intensity on both T1- and T2-weighted images. Pancreatic cysts are a relatively common finding; these cysts are typically quite small but are well demonstrated at MR imaging and MR cholangiopancreatography. Pancreatic duct abnormalities are also occasionally seen. Hepatic manifestations range from hepatomegaly and diffuse fatty infiltration to severe cirrhosis with fibrotic change, regenerative nodules, and portal hypertension. Splenomegaly is often characterized by siderotic nodules that manifest as multiple focal areas of abnormal low signal intensity within the spleen. Biliary manifestations include cholelithiasis, stricturization, and narrowing or dilatation of intra- and extrahepatic bile ducts. Gallbladder abnormalities including microgallbladder are also readily demonstrated. MR cholangiopancreatography can be used to help determine the presence and severity of biliary complications without resorting to more invasive procedures and, in conjunction with MR imaging, may prove useful in the assessment of patients with cystic fibrosis who present with abdominal symptoms that suggest hepatobiliary involvement.
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