Negative MR Research Articles

Polarization dependent asymmetric magneto-resistance features in nanocrystalline diamond films

Polar angle-dependence of magneto-resistance (AMR) in heavily nitrogen-incorporated ultra-nanocrystalline diamond (UNCD) films is recorded by applying high magnetic fields, which shows strong anisotropic features at low temperatures. The temperature-dependence of MR and AMR can reveal transport in the weak-localization regime, which is explained by using a superlattice model for arbitrary values of disorder and angles. While a propagative Fermi surface model explains the negative MR features for low degree of disorder the azimuthal angle-dependent MR shows field dependent anisotropy due to the aligned conducting channels on the layers normal to film growth direction. The analysis of MR and AMR can extract the temperature dependence of dephasing time with respect to the elastic scattering time which not only establishes quasi-two dimensional features in this system but also suggests a potential application in monitoring the performance of UNCD based quantum devices.

Physician self-referral and imaging use appropriateness: negative cervical spine MRI frequency as an assessment metric.

Imaging self-referral is increasingly cited as a contributor to diagnostic imaging overuse. The purpose of this study was to determine whether ownership of MR imaging equipment by ordering physicians influences the frequency of negative cervical spine MR imaging findings. A retrospective review was performed of 500 consecutive cervical spine MRIs ordered by 2 separate referring-physician groups serving the same geographic community. The first group owned the scanners used and received technical fees for their use, while the second group did not. Final reports were reviewed, and for each group, the percentage of negative study findings and the frequency of abnormalities were calculated. The number of concomitant shoulder MRIs was recorded. Five hundred MRIs meeting inclusion criteria were reviewed (250 with financial interest, 250 with no financial interest). Three hundred fifty-two had negative findings (190 with financial interest, 162 with no financial interest); there were 17.3% more scans with negative findings in the financial interest group (P = .006). Among scans with positive findings, there was no significant difference in the mean number of lesions per scan, controlled for age (1.90 with financial interest, 2.19 with no financial interest; P = .23). Patients in the financial interest group were more likely to undergo concomitant shoulder MR imaging (24 with financial interest, 11 with no financial interest; P = .02). Cervical spine MRIs referred by physicians with a financial interest in the imaging equipment used were significantly more likely to have negative findings. There was otherwise a highly similar distribution and severity of disease between the 2 patient samples. Patients in the financial interest group were more likely to undergo concomitant shoulder MR imaging.

Large negative magnetoresistance and ferromagnetism induced by interfacial spins in granular Cr/C films

Cr/C composite films with 7.9 and 8.5at% Cr contents were fabricated by facing-target magnetron sputtering. Cr nanoparticles are embedded in amorphous carbon matrix, and Cr atoms bond with C atoms at the interface. The Cr/C films were found to exhibit ferromagnetism in the temperature range of 2–300K, which is probably induced by uncompensated spins at the surface of Cr nanoparticles. Spin-dependent magnetoresistance (up to −19.5% at 90kOe and 2K) was observed in the Cr/C films. The negative MR originates from the alignment of the uncompensated spins at the interface between nanoparticles and matrix. The spin polarization which comes from the interfacial p–d hybridization was calculated to be 21% and 17% in the Cr/C films with 7.9% and 8.5% Cr, respectively.

Diffusion abnormalities of the corpus callosum in patients receiving bevacizumab for malignant brain tumors: suspected treatment toxicity

Bevacizumab has been reported to cause diffusion restriction in the tumor bed of patients with malignant gliomas. This study evaluated prolonged diffusion restriction, in the corpus callosum (CC), of patients with malignant brain tumors treated with bevacizumab. We retrospectively reviewed our database of patients treated with bevacizumab for malignant brain tumors looking for those with restricted diffusion in the CC. CC ADC ratio measurements were obtained prior to and following treatment. Correlation was made with biopsy (n=3) and MR perfusion (n=7) and PET (n=4). The temporal evolution of these changes relative to therapy was examined with mixed effects regression analysis. Nine patients (eight malignant gliomas, one malignant meningioma) out of 146 patients were found to have developed areas of diffusion restriction in the CC. These areas tended to enlarge and coalesce over serial MRIs and persisted for up to 22months. Hypoperfusion was demonstrated in MR perfusion in 7/7. PET was hypometabolic in all 4. Biopsy of the CC showed no tumor in 3/3. ADC ratio measurements indicated a significant overall effect of time (F(16,60)=11.2; p<0.0001), consistent with persistent diffusion restriction over the measured time periods. Bevacizumab causes prolonged diffusion restriction in the CC. The negative MR perfusion, FDG PET and histopathology suggest this is a toxicity of bevacizumab and not active tumor. Awareness of these changes can assist in patient care.

Large, Negative Magnetoresistance in an Oleic Acid-Coated Fe3O4 Nanocrystal Self-Assembled Film

An oleic acid-coated Fe3O4 nanocrystal self-assembled film was fabricated via drop casting of colloidal particles on a SiO2/Si substrate. The film exhibited bifurcation of the zero-field-cooled and field-cooled magnetizations around 250 K. The nonlinear current-voltage (I-V) characteristics between the source and drain electrodes in both zero and non-zero magnetic fields (H) were observed above and below the bifurcation temperature. A large negative magnetoresistance (MR ≈ -60%) was achieved at 200 K and H = 1 T. Even at 295 K and 0.2 T, the negative MR (∼ -50%) persisted. A Fowler-Nordheim plot and power-law scaling of the I-V characteristics revealed that the current flows through two-dimensional (2D) percolated electron tunneling paths. The enlargement of MR can be attributed to spin-dependent electron tunneling between magnetically coupled Fe3O4 nanocrystals self-assembled in 2D ordered arrays.

Manganese-Loaded Dual-Mesoporous Silica Spheres for Efficient T1- and T2-Weighted Dual Mode Magnetic Resonance Imaging

A novel class of manganese-based dual-mode contrast agents (DMCAs) based on the core-shell structured manganese-loaded dual-mesoporous silica spheres (Mn-DMSSs) for simultaneous T1- and T2-weighted magnetic resonance imaging (MRI) has been successfully reported. The in vitro MR tests demonstrate that the Mn-based DMCAs display an excellent simultaneous T1-weighted and T2-weighted MR imaging effect with a noticeably high T1 relaxivity (r1) of 10.1 mM(-1) s(-1) and a moderately high T2 relaxivity (r2) of 169.7 mM(-1) s(-1). The Mn-based DMCAs exhibit negligible cytotoxicity with >80% cell viability at a concentration of up to 200 μg/mL in human liver carcinoma (HepG2) and mouse macrophage (RAW264.7) cells after 24 h. Confocal laser scanning microscopy (CLSM) results show that the Mn-DMSSs were internalized via endocytosis and located in the cytoplasm but not in the nucleus. The in vivo experiment shows that the signals of rat liver increased by 29% under T1-weighted imaging mode and decreased by 28% under T2-weighted imaging mode in 5 min postinjection of Mn-DMSSs, which reveal that the novel Mn-loaded DMSSs can be used as both positive (T1-weighted) and negative (T2-weighted) MR contrast agents in further biomedical applications.

Presurgical evaluation of refractory temporal lobe epilepsy: Comparison of MR imaging, PET and ictal SPECT in localization of the epileptogenic substrate

PurposeTo compare the sensitivities of MRI, FDG-PET and ictal/SPECT in localization of the epileptogenic substrate in patients with refractory temporal lobe epilepsy. Patients and methodsThis study included 137 patients who received surgical treatment for intractable epilepsy. MRI, FDGPET and ictal 99mTc-HMPAO SPECT were retrospectively reviewed regarding their sensitivity in lateralization of the epileptogenic zone compared to video/EEG, pathological results and surgical outcome. Results104 MR-positive and 33 MR-negative patients were enrolled. In the MR-positive group, MRI, PET and ictal/SPECT were concordant to video/EEG in 72%, 83% and 73%, respectively. When compared to pathological diagnosis, they correctly lateralized the epileptogenic zone in 70%, 87%, and 73%, respectively. In patients with good surgical outcome, they correctly localized the epileptogenic zone in 79%, 88%, and 78%, respectively. In the MR-negative group, PET and ictal/SPECT were concordant with video/EEG in 82% and 58%, respectively and matching with pathological diagnosis in 85% and 56%, respectively. ConclusionPET is the most sensitive method in lateralization of the epileptogenic substrate. The use of MRI, PET and ictal/SPECT as a multimodality approach improves lateralization of the affected zone particularly in cases with negative MR findings and distinguishes patients who will benefit from surgery.

Volume interpolated 3D‐spoiled gradient echo sequence is better than dynamic contrast spin echo sequence for MRI detection of corticotropin secreting pituitary microadenomas

Various techniques have been attempted to increase the yield of magnetic resonance imaging (MRI) for localization of pituitary microadenomas in corticotropin (ACTH)-dependent Cushing's syndrome (CS). To compare the performance of dynamic contrast spin echo (DC-SE) and volume interpolated 3D-spoiled gradient echo (VI-SGE) MR sequences in the diagnostic evaluation of ACTH-dependent CS. Data was analysed retrospectively from a series of ACTH-dependent CS patients treated over 2-year period at a tertiary care referral centre (2009-2011). Thirty-six patients (24 female and 12 male) were diagnosed to have ACTH-dependent CS during the study period. All patients underwent MRI by both sequences during a single examination. Cases with negative and equivocal pituitary MR imaging underwent corticotropin-releasing hormone (CRH) stimulated bilateral inferior petrosal sinus sampling (BIPSS) to confirm pituitary origin of ACTH excess state. Thirty patients were finally diagnosed to have Cushing's disease (CD) [based on histopathology proof of adenoma and/or remission (partial/complete) of hypercortisolism postsurgery]. Six patients were diagnosed to have histopathologically proven ectopic CS. Of 30 patients with CD, 24 patients had microadenomas and 6 patients had macroadenomas. DC-SE MRI sequence was able to identify microadenomas in 16 of 24 patients, whereas postcontrast VI-SGE sequence was able to identify microadenomas in 21 of 24 patients. All six patients of ectopic CS had negative pituitary MR imaging by both techniques (specificity: 100%). VI-SGE MR sequence was better for localization of pituitary microadenomas particularly when DC-SE MR sequence is negative or equivocal and should be used in addition to DC-SE MR sequence for the evaluation of ACTH-dependent CS.

Magnetic and transport properties of Mn-rich Ni35Mn50In15 alloy

The structural, magnetic and transport properties of the newly synthesized Ni35Mn50In15 alloy have been presented. It was observed to form in single phase Hg2CuTi-type structure. The Curie temperature (TC) of the sample is found to be 333K. The magnetization versus field (M–H) curve at 5K and 300K shows existence of ferromagnetic order in the alloy. The resistivity of the alloy varies as T2 at low temperature and as T at high temperature. Above TC, sharp flattening in resistivity is observed. The negative MR of −1.7% is observed at 300K and is found to increase linearly with the magnetic field.

157 Clinical Feature of Patients With False Negative Diffusion-weighted MR Finding in Acute Ischemic Stroke: A Pilot Study

Study Objectives: Diffusion-weighted MRI (DWI) has advantages for the assessment of acute stroke. However, DWI finding in acute ischemic stroke may have been false negative on initial study. The purpose of this study was to estimate the rate of initial false-negative DWI studies in acute ischemic stroke and to identify the characteristics of patients being false-negative DWI.

Magnetically triggered clustering of biotinylated iron oxide nanoparticles in the presence of streptavidinylated enzymes

This work deals with the production and characterization of water-compatible, iron oxide based nanoparticles covered with functional poly(ethylene glycol) (PEG)–biotin surface groups (SPIO–PEG–biotin). Synthesis of the functionalized colloids occurred by incubating the oleate coated particles used as precursor magnetic fluid with anionic liposomes containing 14 mol% of a phospholipid–PEG–biotin conjugate. The latter was prepared by coupling dimyristoylphosphatidylethanolamine (DC14:0PE) to activated α-biotinylamido-ω –N-hydroxy-succinimidcarbonyl–PEG (NHS–PEG–biotin). Physical characterization of the oleate and PEG–biotin iron oxide nanocolloids revealed that they appear as colloidal stable clusters with a hydrodynamic diameter of 160 nm and zeta potentials of − 39 mV (oleate coated particles) and − 14 mV (PEG–biotin covered particles), respectively, as measured by light scattering techniques. Superconducting quantum interference device (SQUID) measurements revealed specific saturation magnetizations of 62–73 emu g−1 Fe3O4 and no hysteresis was observed at 300 K. MR relaxometry at 3 T revealed very high r2 relaxivities and moderately high r1 values. Thus, both nanocolloids can be classified as small, superparamagnetic, negative MR contrast agents. The capacity to functionalize the particles was illustrated by binding streptavidin alkaline phosphatase (SAP). It was found, however, that these complexes become highly aggregated after capturing them on the magnetic filter device during high-gradient magnetophoresis, thereby reducing the accessibility of the SAP.

Non-contrast MR imaging for detecting endoleak after abdominal endovascular aortic repair

Our aim was to investigate the possibility of ruling out endoleak after endovascular aortic repair (EVAR) of abdominal aortic aneurysm (AAA) using non-contrast MRI. Twenty-three patients (20 males, aged 73 ± 8 years) with an EVAR-treated AAA underwent 1.5-T MRI using axial, coronal and sagittal oblique true-FISP sequences. Two blinded and independent readers with 4 (R1) and 2 (R2) years of experience evaluated these images considering an area of even less than 5 mm in diameter with a signal intensity higher than that of normal muscles visible in the excluded aneurysmal sac as a sign of potential endoleak. The final assessment, mainly based on MR angiography and previous examinations, served as reference standard. Out of 23 patients, 13 (57%) were negative for endoleak at final assessment, while the remaining 10 (43%) were positive, with the following type distribution: Ia (n = 4), Ib (n = 2), II (n = 3), and III (n = 1). Sensitivity was 10/10 (100%; CI 95% 69-100%), specificity 7/13 (54%; 25-81%), accuracy 17/23 (74%; 52-90%), PPV 10/16 (63%; 35-85%) and NPV 7/7 (100%; 59-100%) for R1; 9/10 (90%; 56-100%), 8/13 (62%; 32-86%), 17/23 (74%; 52-90%), 9/14 (64%; 35-8%), and 8/9 (89%; 52-100%) for R2, respectively. Inter-reader Cohen κ was 0.810. A negative non-contrast true-FISP MR study can be used to rule out endoleak after EVAR of AAA. This hypothesis may contribute to the reduction of ionizing radiation exposure and contrast material administration for monitoring patients with an EVAR-treated AAA.

Comparison of MR enteroclysis with video capsule endoscopy in the investigation of small-intestinal disease

PurposeTo evaluate the diagnostic accuracy of MR enteroclysis and to compare it to video capsule endoscopy (VCE) in the analysis of suspected small-bowel disease.MethodsWe performed a retrospective analysis of 77 patients who underwent both MR enteroclysis and VCE and compared the findings of these studies with the findings of enteroscopy, surgery, or with the results of clinical follow-up lasting ≥2 years.ResultsFindings included malignant neoplasms (n = 13), benign neoplasms (n = 10), refractory celiac disease (n = 4), Crohn’s disease (n = 2) and miscellaneous conditions (n = 10). Specificity of MR enteroclysis was higher than that of VCE (0.97 vs. 0.84, P = 0.047), whereas sensitivity was similar (0.79 vs. 0.74, P = 0.591). In 2/32 (6.3%) patients with both negative VCE and negative MR enteroclysis a positive diagnosis was established, compared to 5/11 (45.5%) patients in whom VCE was positive and MR enteroclysis was negative (likelihood ratio 8.1; P = 0.004), 9/11 (81.8%) patients in whom MR enteroclysis was positive and VCE was negative (likelihood ratio 23.5; P < 0.0001), and all 23 patients in whom both VCE and MR enteroclysis showed abnormalities (likelihood ratio 60.8; P < 0.0001).ConclusionsVCE and MR enteroclysis are complementary modalities. In our study-population, MR enteroclysis was more specific than VCE, while both produced the same sensitivity.

Abstract 3071: Automated CT Perfusion Processing For the Evaluation of Transient Ischemic Attack

Introduction: The diagnosis of transient ischemic attack (TIA) can be difficult. We evaluated the yield of automated CT perfusion (CTP) in addition to non contrast head CT and CT angiography for the detection of acute ischemic lesions among TIA patients and compare it with multimodal MRI [diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI)] results. Methods: Consecutive patients with a final diagnosis of transient neurological symptoms secondary to ischemia who underwent acute CT, CTP and CTA were enrolled. A subset of the patients underwent multimodal MRI. Presence of symptomatic stenosis was assessed on CTA by the treating team at the time of patient evaluation. The presence and location of acute ischemic lesions was assessed on: CT, CTP, DWI, and PWI. The rater was blinded to the clinical presentation. The presence of a MR or CT perfusion lesion was assessed using TMax. TMax maps for both CT and MR were automatically generated by RApid processing of PerfusIon and Diffusion (RAPID) software. Results: Thirty-three patients were enrolled: median age was 66 years old (IQR 58-82); median ABCD2 score was 4 (IQR 3-5); median delay from symptom onset to CTP was 4.6 hours (IQR 2-9.6). MRI was performed in 23 (70%) patients after a median delay of 20.4 hours (IQR 8.3-30.6) after symptom onset and 5.5 hours (IQR 3.4-20.8) after CTP. No patient experienced recurrence between CTP and MRI. Non-contrast head CT did not demonstrate any acute ischemic lesions. CTA found 3 symptomatic vessel lesions. CTP revealed a focal ischemic lesion in 11 patients (33%). The lesion location concurred with the presumed symptom side in all but one patient, and with the 3 symptomatic vessel lesions found on CTA. DWI was performed in 23 patients, and was positive in 7 (30%). Three of these patients had a negative early CTP. CTP was positive in 3 patients with subsequent normal DWI. MR perfusion was performed in 17 patients and found an acute ischemic lesion in 8 (47%) of them. Four of these MR PWI positive patients also had a positive CTP. In 3 patients with a negative MR PWI, CTP detected an acute ischemic lesion. At least 1 of the 3 modalities (CTP, DWI, PWI) was positive among 10/17 (59%) of patients. Conclusion: The results of this exploratory study suggest that automatically processed CTP increases the yield of head CT and CTA for the evaluation of TIA patients. In some cases CTP found evidence of transient focal ischemia that was not detected by MRI, in others CTP was negative and DWI or PWI was positive. These findings suggest that CTP and MRI may be complementary techniques to confirm the ischemic nature of transient neurological symptoms.

Contrast-Enhanced Magnetic Resonance Imaging Positively Impacts the Management of Some Patients With Rheumatoid Arthritis or Suspected RA

Early diagnosis of rheumatoid arthritis (RA) is important given the availability of highly effective disease-modifying antirheumatic (DMARD) medications, including biologics. However, because of associated risks and cost, accurately assessing disease activity is critical. Because magnetic resonance imaging (MRI) can detect synovitis and bone marrow edema, both of which may precede erosion development, we sought to determine the impact of enhanced MRI on patient management in a group of patients referred for MRI by rheumatologists. After institutional review board approval, we evaluated all hand MRI examinations referred by the rheumatology department for synovitis evaluation between September 2007 and May 2009. The magnetic resonance images were classified as positive or negative and later reviewed by 2 musculoskeletal radiologists. A musculoskeletal radiologist and rheumatologist jointly reviewed the patients' medical records to determine the following: (1) Did the MRI findings alter treatment? (2) Were the treatment alterations beneficial? The study included 48 patients (39 women and 9 men) with a mean age of 51 years (range, 18-79 years). Significant management changes initially occurred in 79% (23/29) of the positive (DMARDs added in 20) and in 11% (2/19) of the negative MR examinations with average follow-up of ~300 days. Eighty percent (16/20) of the patients with DMARDs added experienced symptom improvement, none of the patients whose medications were discontinued experienced symptom relapse, and 18% (4/22) of patients without initial therapeutic changes required delayed treatment modifications. Enhanced MRI significantly altered clinical management in 50% of these patients with RA or suspected RA. Therefore, when the clinical picture in a patient with RA or suspected RA is unclear, enhanced MRI can provide useful guidance for treatment modifications.

Magnetotransport properties of Co-C granular thin films depending on the carbon sputtering power

AbstractCoxC1-x granular films were deposited on Si substrates by a co-sputtering method. A large negative MR of 30.3% was obtained at 2 K for the sample prepared with the sputtering power of 50 W (C) and 4 W (Co). We have studied structural properties of Co-C granular films by Raman spectroscopy. Two peaks (D and G modes) from carbon bonds were clearly observed, and the intensity ratio of two peaks changed with the sputtering power, suggesting that the graphitization was promoted with the sputtering power. It was also revealed that the transport mechanism changed from tunneling to Mott’s variable range hopping and MR decreased with the sputtering power.

The diagnostic value of magnetic resonance arthrography of the shoulder in detection and grading of SLAP lesions: Comparison with arthroscopic findings

PurposeThe purpose of the study is to determine the usefulness of magnetic resonance arthrography (MRA) in diagnosis and grading of superior labrum anterior to posterior (SLAP) lesions of the Glenoid Labrum Compared with surgery Material and methodsThis was a prospective study including fifty nine clinically diagnosed SLAP patients. The study was done during the period from January 2008 to June 2010. All patients were submitted to history taking, clinical examination and conventional MRI examination of the shoulder, MRA was done in patients with negative conventional MRI, all of these patients underwent arthroscopy for diagnosis wither open or arthroscopy for diagnosis and treatment and results were compared with MRA findings. Main outcome measuresSensitivity, specificity, positive and negative predictive values, and overall accuracy of MR arthrography in detection and grading of SLAP lesions of the gelnoid labrum. ResultsOut of fifty nine patients, 25 patients had positive MR findings in conventional MRI, and 34 patients had negative MR findings, who underwent MR arthrography; 10 out of them had normal arthrogram (only 6 of them underwent arthroscopy), 22 had SLAP (superior labrum anterior to posterior) lesions, one had Bankart's lesion and one had internal impingement syndrome. These results were compared with arthroscopy results.The overall sensitivity of MRA in detection of SLAP lesions was 90% while the specificity was 50%, negative predictive value (NPV) was 66.6% and positive predicative value (PPV) was 81.8%. MRA and arthroscopy results were concurrent in 79.3% patients. ConclusionMR arthrography is a sensitive minimally invasive technique for detection and grading of SLAP lesions, it can help in avoiding patients unnecessary diagnostic arthroscopy.

Upper critical field anisotropy in BaFe2−xCoxAs2single crystals synthesized without flux

The upper critical field was measured upto 12 T for three BaFe2-xCoxAs2 single crystals with estimated Co concentrations of x = 0.082, x = 0.117 and x = 0.143. HC2 versus temperature was measured from temperature dependent resistivity, for various applied magnetic fields, H || ab and H || c. The [dHC2/dT]T=Tc, normalized with the corresponding TC, decreases with increasing Co content, for both directions. The anisotropy {\gamma} defined as HC2 || ab / HC2 || c shows a distinct increase with Co content, and its temperature dependence shows a peak close to the TC. Magneto transport measurements, in the spin density wave regions, showed significant negative MR for H || ab and positive MR of H || c in the x = 0.082 sample. The implications of these results are discussed.

Areas suspicious for prostate cancer: MR-guided biopsy in patients with at least one transrectal US-guided biopsy with a negative finding-multiparametric MR imaging for detection and biopsy planning

Areas suspicious for prostate cancer: MR-guided biopsy in patients with at least one transrectal US-guided biopsy with a negative finding-multiparametric MR imaging for detection and biopsy planning

Magnetotransport properties of epitaxial MgO(001)/FeRh films across the antiferromagnet to ferromagnet transition

Interest in the magnetic properties of the ordered equiatomic alloy FeRh has been revived in recent years due to potential applications in heat assisted magnetic recording. This is based on the existence of a first order hysteretic phase transition from strongly anisotropic antiferromagnet (AF) to relatively isotropic ferromagnet (F) upon warming to ∼370 K. Here we investigate this transition, which shows significant coupling between structural, magnetic, and electronic degrees of freedom, via wide temperature range magnetotransport and magnetometry measurements on ordered epitaxial MgO(001)/FeRh(1000 Å) films. Consistent with bulk measurements, a large decrease in resistivity (∼30%) occurs on warming through the transition. The transition temperature shifts with applied magnetic field at −0.75 K/kOe due to the field-induced stabilization of the F phase, leading to large negative magnetoresistance (∼40% in 90 kOe) in the transition region (340–400 K). Isothermal field cycles reveal consistent behavior where the resistivity is controlled by the magnetization changes as the AF/F phase boundary is crossed. In the F state at high temperature anisotropic magnetoresistance (AMR) is observed (maximum amplitude ∼0.45%), in addition to high field negative MR due to field-induced suppression of electron-magnon scattering. The temperature dependence of the AMR reveals clear two-phase coexistence in the hysteresis region, providing a sensitive probe of remnant F regions upon cooling through the transition. This behavior, and the accompanying coercivity enhancement, is discussed in terms of possible two-phase microstructures across the magnetic phase transformation.