Comparison of diffusion tensor,dynamic susceptibility contrast MRI and Tc-Tetrofosmin brain SPECT for the detection of recurrent high-grade glioma

Introduction

Treatment induced necrosis is a relatively frequent finding in patients treated for high-grade glioma. Differentiation by imaging modalities between glioma recurrence and treatment induced necrosis is not always straightforward. This is a comparative study of diffusion tensor imaging (DTI), dynamic susceptibility contrast MRI and ^99mTc-Tetrofosmin brain single-photon emission computed tomography (SPECT) for differentiation of recurrent glioma from treatment induced necrosis.

Methods

A prospective study was made of 30 patients treated for high-grade glioma who had suspected recurrent tumor on follow-up MRI. All had been treated by surgical resection of the tumor followed by standard postoperative radiotherapy with chemotherapy. No residual tumor had been found on brain imaging immediately after the initial treatment. All the patients were studied with dynamic susceptibility contrast brain MRI and, within a week, ^99mTc-Tetrofosmin brain SPECT.

Results

Both ^99mTc-Tetrofosmin brain SPECT and dynamic susceptibility contrast MRI could discriminate between tumor recurrence and treatment induced necrosis with 100% sensitivity and 100% specificity. An apparent diffusion coefficient (ADC) ratio cut-off value of 1.27 could differentiate recurrence from treatment induced necrosis with 65% sensitivity and 100% specificity and a fractional anisotropy (FA) ratio cut-off value of 0.47 could differentiate recurrence from treatment induced necrosis with 57% sensitivity and 100% specificity. A significant correlation was demonstrated between ^99mTc-Tetrofosmin uptake ratio and rCBV (P = 0.003).

Conclusions

Dynamic susceptibility contrast MRI and brain SPECT with ^99mTc-Tetrofosmin had the same accuracy and may be used to detect recurrent tumor following treatment for glioma. DTI also showed promise for the detection of recurrent tumor, but was inferior to both dynamic susceptibility contrast MRI and brain SPECT.     

A new vascular coupling device: Assessment of MRI issues at 3-tesla

Objective

Vascular grafting frequently involves a time-consuming operation. A new vascular coupling device (VCD) made from metallic material was recently developed that may be advantageous because of the reduced operative time and decreased patient risks. Because of the metal, there are safety concerns related to MRI. Therefore, the purpose of this investigation was to use standardized testing techniques to evaluate MRI issues for this VCD in association with a 3-Tesla MR system.

Methods

The VCD (corlife oHG, Hannover, Germany) was evaluated for magnetic field interactions (translational attraction and torque), MRI-related heating, and artifacts at 3-Tesla. MRI-related heating was assessed with the VCD in a gelled-saline-filled phantom with MRI performed at a whole body averaged SAR of 2.9-W/kg for 15-min. Artifacts were assessed using T1-weighted, spin echo, and gradient echo pulse sequences.

Results

The VCD exhibited minor magnetic field interactions and minimal heating (maximum temperature elevation, 1.8 °C). Artifacts were relatively small in relation to the size and shape of this implant. The lumen of the VCD could not be visualized using the gradient echo pulse sequence.

Conclusions

The metallic VCD that underwent evaluation is MR conditional for a patient undergoing an MRI procedure at 3-Tesla or less.     

In vitro assessment of 3-T MRI issues for a bioabsorbable,coronary artery scaffold with metallic markers

Objective

Coronary artery stents are made from metallic mesh and, therefore, to ensure patient safety, these implants must be evaluated to determine risks associated with MRI. Recently, bioabsorbable scaffolds, which have metallic markers, have been developed for use in the coronary arteries. Because of the metallic materials, these implants may present issues for patients undergoing MRI. Therefore, the objective of this investigation was to assess MRI issues (i.e., magnetic field interactions, MRI-related heating, and artifacts at 3 T) for a new bioabsorbable, coronary artery scaffold with metallic markers.

Methods

A bioabsorbable, coronary artery scaffold (Mirage Microfiber Scaffold) underwent assessments for magnetic field interactions, MRI-related heating, and artifacts at 3-Tesla using standard techniques. MRI-related heating was evaluated with the scaffold placed in a gelled-saline-filled phantom and MRI was performed at an MR system reported, whole body averaged SAR of 2.9 W/kg for 15 minutes. Artifacts were characterized using T1-weighted spin echo and gradient echo, pulse sequences.

Results

There were no magnetic field interactions. The highest temperature rise was 1.6 °C (highest background temperature rise, 1.6 °C). Artifacts were relatively small in relation to the size and shape of this coronary artery scaffold. Notably, the lumen of the scaffold could be visualized on the GRE pulse sequence.

Conclusion

The results demonstrated that the coronary artery scaffold is acceptable (or “MR conditional,” using current MRI labeling terminology) for a patient undergoing an MRI procedure at 3 T or less. To our knowledge, this is the first bioabsorbable, coronary artery scaffold that has been evaluated for MRI issues.     

Feasibility of fat-saturated T2-weighted magnetic resonance imaging with slice encoding for metal artifact correction (SEMAC) at 3T

Background and Purpose

Fluid-sensitive MR imaging in postoperative evaluation is important, however, metallic artifacts is inevitable. The purpose is to investigate the feasibility of fat-saturated slice encoding for metal artifact correction (SEMAC)-corrected T2-weighted magnetic resonance (MR) at 3T in patients with spinal prostheses.

Methods

Following institutional review board approval, 27 SEMAC-encoded spinal MRs between September 2012 and October 2013 in patients with spinal metallic prostheses were analyzed. The MR images were scanned on a 3T MR system including SEMAC-corrected and uncorrected fast spin echo (FSE) T2-weighted MR images with fat-saturation. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images using a five-point scale in terms of artifact reduction around the prosthesis, visualization of the prosthesis and pedicle, and intervertebral neural foramina. Quantitative assessments were performed by calculating the ratio of signal intensity from the fixated vertebra and that from upper level vertebra. For statistical analyses, paired t-test was used.

Results

Fat-saturated SEMAC-corrected T2-weighted MR images enabled significantly improved metallic artifact reduction (P < 0.05). Quantitative evaluation of the signal intensity ratio of screw-fixated vertebra and upper level vertebra showed a significantly lower ratio on fat-saturated SEMAC images (P < 0.05), however, the high signal intensity of signal pile-up could be not completely corrected.

Conclusion

SEMAC correction in fat-suppressed T2-weighted MR images can overcome the signal loss of metallic artifacts and provide improved delineation of the pedicle screw and peri-prosthetic region. Signal pile-up, however, could not be corrected completely, therefore readers should be cautious in the evaluation of marrow around the prosthesis.     

Usefulness of slice encoding for metal artifact correction (SEMAC) for reducing metallic artifacts in 3-T MRI

Purpose

The purpose of the study was to assess the usefulness of slice encoding for metal artifact correction (SEMAC) in 3.0-T magnetic resonance (MR) in minimizing metallic artifacts in patients with spinal prostheses.

Materials and Methods

Institutional review board approval and informed consent were obtained for this study. Twenty-seven spine MR scans were performed with metal artifact reduction SEMAC between May 2011 and July 2012 in patients with metallic devices. The MR scans were performed on a 3-T MR system (Achieva; Philips Healthcare, Best, the Netherlands) including SEMAC-corrected T2-weighted axial/sagittal images and two-dimensional fast spin echo (FSE) axial/sagittal images. The SEMAC-corrected images were compared to conventional T2-weighted FSE images. Two musculoskeletal radiologists qualitatively analyzed the images in terms of visualization of the pedicle, vertebral body, dural sac, intervertebral disc, intervertebral neural foramina, screws and metallic artifacts. The paired images were rated using a 5-point scale. P values less than .05 were considered to indicate statistically significant differences.

Results

The SEMAC-corrected MR images significantly reduced the metal-related artifacts. The T2-weighted images with SEMAC sequences enabled significantly improved periprosthetic visualizations of the pedicle, vertebral body, dural sac and neural foramina, with the exception of the intervertebral disc (P < .05). In addition, there was significant improvement in prosthesis visualization (P < .05).

Conclusion

MR images with SEMAC can reduce metal-related artifacts, providing improved delineation of the prosthesis and periprosthetic region. However, for the evaluation of the intervertebral disc, the SEMAC-corrected MR images showed no significant benefits.     

Assessment of MRI issues for the Argus II retinal prosthesis

Objective

The objective was to evaluate magnetic resonance imaging (MRI) issues (magnetic field interactions, heating, artifacts and functional alterations) at 1.5 T and 3 T for the Argus II Retinal Prosthesis (Second Sight Medical Products, Sylmar, CA, USA).

Materials and Methods

Standardized protocols were used to assess magnetic field interactions (translational attraction and torque; 3 T, worst case), MRI-related heating (1.5 and 3 T), artifacts (3 T; worst case) and functional changes (1.5 and 3 T) associated with MRI.

Results

The magnetic field interactions were acceptable. MRI-related heating, which was studied at a relatively high, MR system-reported whole body averaged specific absorption rates, will not pose a hazard to the patient under the conditions used for testing. While artifacts were “moderate” in relation to the dimensions of the Argus II Retinal Prosthesis, optimization of MRI parameters can reduce the size of the artifacts. Exposures to MRI conditions at 1.5 and 3 T did not damage or alter the functional aspects of the Argus II Retinal Prosthesis.

Conclusions

In consideration of the test results, a patient with the Argus II Retinal Prosthesis may undergo MRI at 1.5 T or 3 T when specific guidelines and MRI conditions are followed, including those advised by the manufacturer.     

Evaluation of MRI issues at 3-Tesla for a hospital identification (ID) wristband

Background and Purpose

A recent report suggested that a serious burn injury was due to the presence of the identification (ID) wristband. As such, in lieu of removing or padding hospital ID wristbands in all patients prior to magnetic resonance imaging (MRI), testing may be performed to characterize risks for ID wristbands. Therefore, the purpose of this investigation was to evaluate the magnetic field interactions, heating and artifacts at 3 T for a hospital ID wristband.

Materials and Methods

Standardized test methods were used to evaluate magnetic field interactions, MRI-related heating, and artifacts at 3 T for a hospital ID wristband.

Results

There were no magnetic field interactions. MRI-related heating evaluated at a relatively high, MR system-reported, whole body-averaged specific absorption rate (2.9 W/kg) did not increase above the background level. The artifacts related to the ink used for printing were “small” for one toner and “large” for the other in relation to the dimensions of the printing.

Conclusions

Based on the tests performed, this particular hospital ID wristband is considered MR safe and will not pose a hazard to a patient undergoing an MRI examination. Importantly, it is not necessary to remove this item for a patient referred for MRI.     

Magnetic resonance image enhancement using stochastic resonance in Fourier domain

Objective

In general, low-field MRI scanners such as the 0.5- and 1-T ones produce images that are poor in quality. The motivation of this study was to lessen the noise and enhance the signal such that the image quality is improved. Here, we propose a new approach using stochastic resonance (SR)-based transform in Fourier space for the enhancement of magnetic resonance images of brain lesions, by utilizing an optimized level of Gaussian fluctuation that maximizes signal-to-noise ratio (SNR).

Materials and Methods

We acquired the T1-weighted MR image of the brain in DICOM format. We processed the original MR image using the proposed SR procedure. We then tested our approach on about 60 patients of different age groups with different lesions, such as arteriovenous malformation, benign lesion and malignant tumor, and illustrated the image enhancement by using just-noticeable difference visually as well as by utilizing the relative enhancement factor quantitatively.

Results

Our method can restore the original image from noisy image and optimally enhance the edges or boundaries of the tissues, clarify indistinct structural brain lesions without producing ringing artifacts, as well as delineate the edematous area, active tumor zone, lesion heterogeneity or morphology, and vascular abnormality. The proposed technique improves the enhancement factor better than the conventional techniques like the Wiener- and wavelet-based procedures.

Conclusions

The proposed method can readily enhance the image fusing a unique constructive interaction of noise and signal, and enables improved diagnosis over conventional methods. The approach well illustrates the novel potential of using a small amount of Gaussian noise to improve the image quality.     

Evaluation of MRI artifacts at 3 Tesla for 38 commonly used cosmetics

Purpose

To evaluate MRI artifacts at 3-Tesla for 38 commonly used cosmetics.

Materials and Methods

Thirty-eight cosmetics (16, nail polishes; 5, eyeliners; 3, mascaras; 10, eye shadows; 1, lip gloss; 1, body lotion; 1, body glitter, and 1, hair loss concealer) underwent evaluation for MRI artifacts at 3-Tesla. The cosmetics were applied a copper-sulfate-filled, phantom and initially assessed using a “screening” gradient echo (GRE) pulse sequence. Of the 38 different cosmetics, 14 (37%) exhibited artifacts. For these 14 cosmetics, additional characterization of artifacts was performed using a GRE pulse sequence. A qualitative scale was applied to characterize the artifact size.

Results

Artifacts were observed, as follows: 2, nail polishes; 5, eyeliners; 3, mascaras; 3, eye shadows; 1, hair loss concealer. Artifact size ranged from small (eye shadow) to very large (hair loss concealer) and tended to be associated with the presence of iron oxide or other metal-based ingredient.

Conclusions

Commonly used cosmetics caused artifacts that may create issues if the area of interest is the same as where the cosmetic was applied or if its presence was unknown, thus, potentially causing it to be construed as pathology. Therefore, these findings have important implications for patients referred for MRI examinations.     

A next-generation,flow-diverting implant used to treat brain aneurysms: in vitro evaluation of magnetic field interactions,heating and artifacts at 3-T

Background and Purpose

Fine-mesh braided, stent-like structures (flow diverters) have been proposed for treatment of brain aneurysms. To date, the safety of performing magnetic resonance imaging (MRI) in patients with these implants is unknown. Therefore, the purpose of this study was to evaluate MRI issues at 3-T for a new flow-diverting implant used to treat brain aneurysms.

Methods

The Surpass NeuroEndoGraft (Surpass Medical, Ltd., Tel Aviv, Israel) underwent evaluation for magnetic field interactions, MRI-related heating and artifacts using standardized techniques. Magnetic field interactions were assessed for this implant with regard to translational attraction (i.e., using the deflection angle technique) and torque (qualitative assessment method). MRI-related heating was evaluated by placing the implant in a gelled-saline-filled, head/torso phantom and performing MRI using a transmit/receive radiofrequency body coil at a whole-body-averaged specific absorption rate of 2.9 W/kg for 15 min. Artifacts were characterized using T1-weighted, spin echo (SE) and gradient echo (GRE) pulse sequences.

Results

The Surpass NeuroEndoGraft exhibited minor magnetic field interactions (21° deflection angle and no torque), which were acceptable from a safety consideration. Heating was not substantial, with the highest temperature change being 2.3°C (background temperature rise without the implant was 1.5°C). Artifacts may create issues if the area of interest is in the same area or close to this implant.

Conclusions

The findings demonstrated that it would be acceptable for patients with this next-generation, flow-diverting implant to undergo MRI at 3-T or less.     

In vitro assessment of MRI issues at 3-Tesla for a breast tissue expander with a remote port

Objectives

A patient with a breast tissue expander may require a diagnostic assessment using magnetic resonance imaging (MRI). To ensure patient safety, this type of implant must undergo in vitro MRI testing using proper techniques. Therefore, this investigation evaluated MRI issues (i.e., magnetic field interactions, heating, and artifacts) at 3-Tesla for a breast tissue expander with a remote port.

Methods

A breast tissue expander with a remote port (Integra Breast Tissue Expander, Model 3612-06 with Standard Remote Port, PMT Corporation, Chanhassen, MN) underwent evaluation for magnetic field interactions (translational attraction and torque), MRI-related heating, and artifacts using standardized techniques. Heating was evaluated by placing the implant in a gelled-saline-filled phantom and MRI was performed using a transmit/receive RF body coil at an MR system reported, whole body averaged specific absorption rate of 2.9-W/kg. Artifacts were characterized using T1-weighted and GRE pulse sequences.

Results

Magnetic field interactions were not substantial and, thus, will not pose a hazard to a patient in a 3-Tesla or less MRI environment. The highest temperature rise was 1.7 °C, which is physiologically inconsequential. Artifacts were large in relation to the remote port and metal connector of the implant but will only present problems if the MR imaging area of interest is where these components are located.

Conclusions

A patient with this breast tissue expander with a remote port may safely undergo MRI at 3-Tesla or less under the conditions used for this investigation. These findings are the first reported at 3-Tesla for a tissue expander.     

Isotropic proton-density-weighted high-resolution MRI for volume measurement of reconstructed orbital fractures--a comparison with multislice CT

Objective

The cause of enophthalmos as a late complication after orbital reconstruction is poorly investigated. Multislice CT (MSCT) is usually employed for its assessment, in spite of limitations regarding soft tissue depiction/imaging, as well as the implication of radiation and production of artifacts. Magnetic resonance imaging (MRI) has been shown to be a valuable alternative. The aim of this study was to establish a bony and soft tissue orbital volume calculation method based on different high-resolution MRI sequences compared to MSCT.

Materials and Methods

Thirty-seven patients were included in this prospective study investigating the origin of enophthalmos present 3–4 months after complex orbital reconstruction. Morphological and dimensional changes of the orbit, eye globes, extraocular muscles and fat content were investigated 3–4 months after surgery. To assess the site and size of bony and soft tissue changes in the traumatized orbits, we used MSCT and MR images as well as corresponding 3-D reconstructions.

Results

All enophthalmic orbits revealed a significant bony volume increase compared to the contralateral side as well as a reduced sagittal eye projection. Mean orbital volume enlargements of 1.0 cm³ lead to 0.93 mm enophthalmos (P<.05). Hardly any fatty atrophy could be depicted by the different MRI techniques.

Conclusions

For soft tissue depiction of the orbit, MRI was superior to MSCT. Particularly, proton density weighting proved to be the best sequence for soft tissue volume segmentation, allowing determination of the cause and degree of posttraumatic enophthalmos in reconstructed orbits.     

Management of branch-duct intraductal papillary mucinous neoplasms of the pancreas: observation with MR imaging

Purpose

To evaluate the clinical outcomes of conservative management by observation with MRI of patients with branch-duct intraductal papillary mucinous neoplasms (BD-IPMNs).

Materials and Methods

Twenty-three consecutive patients, who were followed up by MRI with magnetic resonance cholangiopancreatography (MRCP) over a period of more than 9 months after initial MRI examinations, were enrolled in this study. On MRI, number of lesions, the maximum diameter of BD-IPMNs, lesion location, the presence of associated dilatation of main pancreatic duct (MPD), the presence of enhancing mural nodules within the lesion and the presence of interval change were retrospectively reviewed on initial and follow-up MR images in consensus by two radiologists. All patients were evaluated to search for evidence of malignant progression of disease.

Results

The follow-up period ranged from 10 to 96 months (mean, 37 months). On initial MRI with MRCP, a total of 39 lesions were found in 23 patients. The maximum diameter of BD-IPMNs ranged between 6 and 32 mm, with a mean of 12 mm. Thirty-four lesions (87%) of 19 patients remained unchanged in the maximum diameter. Five lesions (13%) of four patients showed an increase in the maximum diameter. Enhancing mural nodules were not found in any individual, neither on the initial MRI study nor on the follow-up studies. There was no patient who had evidence of local aggressive growth of tumor or evidence of metastases to distant sites.

Conclusion

Our study suggests that branch-duct IPMNs without enhancing mural nodules are essentially benign and should be managed nonoperatively through observation by MRI.     

Validation of optimal DCE-MRI perfusion threshold to classify at-risk tumor imaging voxels in heterogeneous cervical cancer for outcome prediction

Purpose

To classify tumor imaging voxels at-risk for treatment failure within the heterogeneous cervical cancer using DCE MRI and determine optimal voxel's DCE threshold values at different treatment time points for early prediction of treatment failure.

Material and Method

DCE-MRI from 102 patients with stage IB2–IVB cervical cancer was obtained at 3 different treatment time points: before (MRI 1) and during treatment (MRI 2 at 2–2.5 weeks and MRI 3 at 4–5 weeks). For each tumor voxel, the plateau signal intensity (SI) was derived from its time-SI curve from the DCE MRI. The optimal SI thresholds to classify the at-risk tumor voxels was determined by the maximal area under the curve using ROC analysis when varies SI value from 1.0 to 3.0 and correlates with treatment outcome.

Results

The optimal SI thresholds for MRI 1, 2 and 3 were 2.2, 2.2 and 2.1 for significant differentiation between local recurrence/control, respectively, and 1.8, 2.1 and 2.2 for death/survival, respectively.

Conclusion

Optimal SI thresholds are clinically validated to quantify at-risk tumor voxels which vary with time. A single universal threshold (SI = 1.9) was identified for all 3 treatment time points and remained significant for the early prediction of treatment failure.     

Occipital lobe's cortical thinning in ametropic amblyopia

Background and Purpose

The present study was designed to detect the abnormalities of the cortical thickness in children with ametropic amblyopia by a computer-aided MRI technique.

Methods

Nine children with ametropic amblyopia and eight age-matched normal controls underwent MRI brain scanning that was performed on a Siemens Avanto 1.5-T scanner, and standard T₁-weighted high-resolution anatomic scans of magnetization-prepared rapid gradient echo (MPRAGE) sequence were obtained. For the cortical thickness analysis, 3D MPRAGE images were processed with FreeSurfer software package (http://www.nmr.mgh.harvard.edu/freesurfer/), and the cortical thicknesses were compared between the patient group and the normal control group.

Results

The cortical thicknesses of the lingual and pericalcarine areas in the left hemisphere and of the cuneus, lateraloccipital and lingual areas in the right hemisphere in the amblyopic group were significantly thinner than those of the control group (P<.05).

Conclusion

The changes in cortical thickness of several occipital regions in amblyopic patients may be important in the diagnosis and treatment of this disease.     

Measurements of RF heating during 3.0-T MRI of a pig implanted with deep brain stimulator

Purpose

To present preliminary, in vivo temperature measurements during MRI of a pig implanted with a deep brain stimulation (DBS) system.

Materials and Methods

DBS system (Medtronic Inc., Minneapolis, MN) was implanted in the brain of an anesthetized pig. 3.0-T MRI was performed with a T/R head coil using the low-SAR GRE EPI and IR-prepped GRE sequences (SAR: 0.42 and 0.39 W/kg, respectively), and the high-SAR 4-echo RF spin echo (SAR: 2.9 W/kg). Fluoroptic thermometry was used to directly measure RF-related heating at the DBS electrodes, and at the implantable pulse generator (IPG). For reference the measurements were repeated in the same pig at 1.5 T and, at both field strengths, in a phantom.

Results

At 3.0 T, the maximal temperature elevations at DBS electrodes were 0.46 °C and 2.3 °C, for the low- and high-SAR sequences, respectively. No heating was observed on the implanted IPG during any of the measurements. Measurements of in vivo heating differed from those obtained in the phantom.

Conclusion

The 3.0-T MRI using GRE EPI and IR-prepped GRE sequences resulted in local temperature elevations at DBS electrodes of no more than 0.46 °C. Although no extrapolation should be made to human exams and much further study will be needed, these preliminary data are encouraging for the future use 3.0-T MRI in patients with DBS.     

The use of T2*-weighted multi-echo GRE imaging as a novel method to diagnose hepatocellular carcinoma compared with gadolinium-enhanced MRI: a feasibility study

Background

The goal of the study was to assess a T2*-weighted MRI sequence for the ability to identify hepatocellular carcinoma (HCC).

Methods

Hepatic iron deposition, which is common in chronic liver disease (CLD), may increase the conspicuity of HCC on GRE imaging due to increased T2* signal decay in liver parenchyma. In this study, a breath-hold T2*-weighted MRI sequence was evaluated by a blinded observer for HCC and the results compared to a reference standard of gadolinium-enhanced MRI in these same patients. Forty-one patients (mean age 56.2 years; 17 females) were included in this approved, retrospective study.

Results

By the reference standard, 14 of 41 patients had a total of 25 HCCs. The sensitivity of the T2*-weighted MR sequence for identifying HCC, per lesion, was 60%, while the specificity was 100%. There was a significantly lower T2* value of liver parenchyma in patients with HCC identified by the T2*-weighted sequence than in those with HCCs which were not identified by the T2*-weighted sequence (27.8±2.2 vs. 21.9±2.1 ms; P=.02).

Conclusions

A T2*-weighted MRI sequence can identify HCC in patients with CLD. This technique may be beneficial for imaging of patients contraindicated for gadolinium.     

A new perceptual difference model for diagnostically relevant quantitative image quality evaluation: A preliminary study

Purpose

Most objective image quality metrics average over a wide range of image degradations. However, human clinicians demonstrate bias toward different types of artifacts. Here, we aim to create a perceptual difference model based on Case-PDM that mimics the preference of human observers toward different artifacts.

Method

We measured artifact disturbance to observers and calibrated the novel perceptual difference model (PDM). To tune the new model, which we call Artifact-PDM, degradations were synthetically added to three healthy brain MR data sets. Four types of artifacts (noise, blur, aliasing or “oil painting” which shows up as flattened, over-smoothened regions) of standard compressed sensing (CS) reconstruction, within a reasonable range of artifact severity, as measured by both PDM and visual inspection, were considered. After the model parameters were tuned by each synthetic image, we used a functional measurement theory pair-comparison experiment to measure the disturbance of each artifact to human observers and determine the weights of each artifact's PDM score. To validate Artifact-PDM, human ratings obtained from a Double Stimulus Continuous Quality Scale experiment were compared to the model for noise, blur, aliasing, oil painting and overall qualities using a large set of CS-reconstructed MR images of varying quality. Finally, we used this new approach to compare CS to GRAPPA, a parallel MRI reconstruction algorithm.

Results

We found that, for the same Artifact-PDM score, the human observer found incoherent aliasing to be the most disturbing and noise the least. Artifact-PDM results were highly correlated to human observers in both experiments. Optimized CS reconstruction quality compared favorably to GRAPPA's for the same sampling ratio.

Conclusions

We conclude our novel metric can faithfully represent human observer artifact evaluation and can be useful in evaluating CS and GRAPPA reconstruction algorithms, especially in studying artifact trade-offs.     

Influence of thickening of the inner skull table on intracranial volume measurement in older people

Introduction

It is generally assumed that intracranial volume (ICV) remains constant after peaking in early adulthood. Thus ICV is used as a ‘proxy’ for original brain size when trying to estimate brain atrophy in older people in neuroimaging studies. However, physiological changes in the skull, such as thickening of the frontal inner table, are relatively common in older age and will reduce ICV. The potential influence that inner table skull thickening may have on ICV measurement in old age has yet to be investigated.

Methods

We selected 60 (31 males, 29 females) representative older adults aged 71.1–74.3 years from a community-dwelling ageing cohort, the Lothian Birth Cohort 1936. A semi-automatically derived current ICV measurement obtained from high resolution T1-weighted volume scans was compared to the estimated original ICV by excluding inner skull table thickening using expert manual image processing.

Results

Inner table skull thickening reduced ICV from an estimated original 1480.0 ml to a current 1409.1 ml, a median decrease of 7.3% (Z = − 6.334; p < 0.001), and this reduction was more prominent in women than men (median decrease 114.6 vs. 101.9 ml respectively). This led to potential significant underestimations of brain atrophy in this sample by 5.3% (p < 0.001) and obscured potential gender differences.

Conclusions

The effects of skull thickening are important to consider when conducting research in ageing, as they can obscure gender differences and result in underestimation of brain atrophy. Research into reliable methods of determining the estimated original ICV is required for research into brain ageing.