High-b diffusivity of MS lesions in cervical spinal cord using ultrahigh-b DWI (UHb-DWI).

PURPOSE: The purpose of this study was to investigate UHb-rDWI signal in white matter tracts of the cervical spinal cord (CSC) and compare quantitative values between healthy control WM with both MS NAWM and MS WM lesions. METHODS: UHb-rDWI experiments were performed on (a) 7 MS patients with recently active or chronic lesions in CSC and on (b) 7 healthy control of similar age range and gender distribution to MS subjects. All MRI data were acquired using clinical 3T MRI system. Axial high-b diffusion images were acquired using 2D single-shot DW stimulated EPI with reduced FOV and a CSC-dedicated 8 channel array coil. High-b diffusion coefficient DH was estimated by fitting the signal-b curve to a double or single-exponential function. RESULTS: The high-b diffusivity DH values were measured as (0.767 ± 0.297) × 10-3 mm2/s in the posterior column lesions, averaged over 6 MS patients, and 0.587 × 10-3 mm2/s in the corticospinal tract for another patient. The averaged DH values of the 7 healthy volunteers from the posterior and lateral column were (0.0312 ± 0.0306) × 10-3 and (0.0505 ± 0.0205) × 10-3 mm2/s, respectively. UHb-rDWI signal-b curves of the MS patients revealed to noticeably behave differently to that of the healthy controls. The patient signal-b curves decayed with greater high-b decay constants to reach lower signal intensities relative to signal-b curves of the healthy controls. CONCLUSION: UHb-DWI of the CSC reveals a marked difference in signal-b-curves and DH values in MS lesions compared to NAWM and healthy control WM. Based on physical principles, we interpret these altered observations of quantitative diffusion values to be indicative of demyelination. Further studies in animal models will be required to fully interpret UHb-DWI quantitative diffusion values during demyelination and remyelination.

Changes of Neurotransmitters in Youth with Internet and Smartphone Addiction: A Comparison with Healthy Controls and Changes after Cognitive Behavioral Therapy.

BACKGROUND AND PURPOSE: Neurotransmitter changes in youth addicted to the Internet and smartphone were compared with normal controls and in subjects after cognitive behavioral therapy. In addition, the correlations between neurotransmitters and affective factors were investigated. MATERIALS AND METHODS: Nineteen young people with Internet and smartphone addiction and 19 sex- and age-matched healthy controls (male/female ratio, 9:10; mean age, 15.47 ± 3.06 years) were included. Twelve teenagers with Internet and smartphone addiction (male/female ratio, 8:4; mean age, 14.99 ± 1.95 years) participated in 9 weeks of cognitive behavioral therapy. Meshcher-Garwood point-resolved spectroscopy was used to measure γ-aminobutyric acid and Glx levels in the anterior cingulate cortex. The γ-aminobutyric acid and Glx levels in the addicted group were compared with those in controls and after cognitive behavioral therapy. The γ-aminobutyric acid and Glx levels correlated with clinical scales of Internet and smartphone addiction, impulsiveness, depression, anxiety, insomnia, and sleep quality. RESULTS: Brain parenchymal and gray matter volume-adjusted γ-aminobutyric acid-to-creatine ratios were higher in subjects with Internet and smartphone addiction (P = .028 and .016). After therapy, brain parenchymal- and gray matter volume-adjusted γ-aminobutyric acid-to-creatine ratios were decreased (P = .034 and .026). The Glx level was not statistically significant in subjects with Internet and smartphone addiction compared with controls and posttherapy status. Brain parenchymal- and gray matter volume-adjusted γ-aminobutyric acid-to-creatine ratios correlated with clinical scales of Internet and smartphone addictions, depression, and anxiety. Glx/Cr was negatively correlated with insomnia and sleep quality scales. CONCLUSIONS: The high γ-aminobutyric acid levels and disrupted balance of γ-aminobutyric acid-to-Glx including glutamate in the anterior cingulate cortex may contribute to understanding the pathophysiology and treatment of Internet and smartphone addiction and associated comorbidities.

Crepidiastrum denticulatum Extract Ameliorates Kidney Ischemia-Reperfusion Injury in Mice.

BACKGROUND: Crepidiastrum denticulatum (CD) is a well-known, traditionally consumed vegetable in Korea, which was recently reported to contain bioactive compounds with detoxification and antioxidant properties. Ischemia-reperfusion injury (IRI) is a major problem after renal transplantation. Furthermore, inflammatory responses to IRI exacerbate the resultant renal injury. In the present study, we investigated whether CD extract exhibits renoprotective effects against IR-induced acute kidney injury in mice. MATERIALS AND METHODS: Renal IRI was induced in male C57BL/6 mice by bilateral renal pedicle occlusion for 30 minutes followed by reperfusion for 48 hours. CD extract (75 mg/kg) was administered orally 5 days before IRI. RESULTS: Treatment with CD extract significantly decreased blood urea nitrogen and serum creatinine levels as well as kidney tubular injury. CD also prevented IRI-induced renal glutathione depletion and increased malondialdehyde levels. Western blotting and reverse transcriptase polymerase chain reaction indicated that CD extract significantly attenuates inducible nitric oxide synthase and toll-like receptor 2/4 protein levels 48 h after IRI. The expression of tumor necrosis factor-α and interleukin-1ß was significantly decreased in the CD extract treatment group. CONCLUSION: CD extract improved acute renal IRI through its antioxidant and anti-inflammatory effects. These findings suggest that CD extract is a potential therapeutic agent for acute ischemia-induced renal damage.

Protective Effect of Polydeoxyribonucleotide Against Renal Ischemia-Reperfusion Injury in Mice.

BACKGROUND: Polydeoxyribonucleotide (PDRN) is an A2A receptor agonist that induces vascular endothelial growth factor (VEGF) production during the pathological condition of low tissue perfusion. Ischemia-reperfusion injury (IRI) is a major problem after renal transplantation. In the present study, we investigated whether PDRN exhibits reno-protective effects against ischemia-reperfusion-induced acute kidney injury in mice. METHODS: Renal ischemia-reperfusion injury was induced in male C57BL/6 mice by bilateral renal pedicle occlusion for 30 minutes, followed by reperfusion for 48 hours. PDRN (8 mg/kg body weight intraperitoneally) was administered 30 minutes before IRI. RESULTS: Treatment with PDRN significantly decreased neutrophil gelatinase-associated lipocalin levels in the urine, blood urea nitrogen level, and serum creatinine levels as well as kidney tubular injury. Western blotting showed that PDRN significantly increased the levels of vascular endothelial growth factor and B-cell lymphoma protein and attenuated p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, inducible nitric oxide synthase, and Bcl-2-associated X protein levels 48 hours after IRI. CONCLUSIONS: Our findings suggest that PDRN is a potential therapeutic agent for acute ischemia-induced renal damage.

Protective effect of eupatilin against renal ischemia-reperfusion injury in mice.

BACKGROUND: Eupatilin, a pharmacologically active flavone derived from Artemisia species, is known to have antioxidant and anti-inflammatory activities. Ischemia-reperfusion injury (IRI) is a major complication after renal transplantation, with inflammatory responses to IRI exacerbating the resultant renal injury. In the present study, we investigated whether eupatilin exhibits renoprotective activities against ischemia-reperfusion-induced acute kidney injury in mice. MATERIALS AND METHODS: Renal IRI was induced in male C57BL/6 mice by bilateral renal pedicle occlusion for 30 minutes followed by reperfusion for 48 hours. Eupatilin (10 mg/kg body weight p.o.) was administered 4 days before IRI. RESULTS: Treatment with eupatilin significantly decreased neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels in urine, blood urea nitrogen level, and serum creatinine levels, as well as kidney tubular injury. Western blotting indicated that eupatilin significantly increased the levels of heat shock protein 70 and B-cell lymphoma protein, and it attenuated inducible nitric oxide synthase, Bcl-2-associated X protein, and caspase-3 levels 48 hours after IRI. CONCLUSION: Our findings suggest that eupatilin is a promising therapeutic agent against acute ischemia-induced renal damage.

Short-term training alters the control of mitochondrial respiration rate before maximal oxidative ATP synthesis.

AIM: Short-term exercise training may induce metabolic and performance adaptations before any changes in mitochondrial enzyme potential. However, there has not been a study that has directly assessed changes in mitochondrial oxidative capacity or metabolic control as a consequence of such training in vivo. Therefore, we used (31) P-magnetic resonance spectroscopy ((31) P-MRS) to examine the effect of short-term plantar flexion exercise training on phosphocreatine (PCr) recovery kinetics and the control of respiration rate. METHOD: To this aim, we investigated 12 healthy men, experienced with this exercise modality (TRA), and 7 time-control subjects (TC). RESULTS: After 5 days of training, maximum work rate during incremental plantar flexion exercise was significantly improved (P < 0.01). During the recovery period, the maximal rate of oxidative adenosine triphosphate synthesis (PRE: 28 ± 13 mm min(-1) ; POST: 26 ± 15 mm min(-1) ) and the PCr recovery time constant (PRE: 31 ± 19 s; POST: 29 ± 16) were not significantly altered. In contrast, the Hill coefficient (nH ) describing the co-operativity between respiration rate and ADP was significantly increased in TRA (PRE: nH = 2.7 ± 1.4; POST: nH = 3.4 ± 1.9, P < 0.05). Meanwhile, there were no systematic variations in any of these variables in TC. CONCLUSION: This study reveals that 5 days of training induces rapid adaptation in the allosteric control of respiration rate by ADP before any substantial improvement in muscle oxidative capacity occurs.

High-resolution diffusion-weighted imaging of neck lymph nodes using 2D-single-shot interleaved multiple inner volume imaging diffusion-weighted echo-planar imaging at 3T.

BACKGROUND AND PURPOSE: 2D-ss-IMIV-DWEPI is an ss-DWEPI with greatly reduced geometric distortion. The purposes of this paper are to 1) evaluate of the utility of 2D-ss-IMIV-DWEPI for high-resolution neck LN imaging; 2) determine whether 2D-ss-IMIV-DWEPI can depict normal LN hilum; and 3) evaluate whether the inclusion of LN hilum within ROIs affects the measured LN ADC. MATERIALS AND METHODS: HR-DWI was acquired with 1-mm² in-plane resolution and 2-mm section thickness by using 2D-ss-IMIV-DWEPI. In total, 58 LNs from 18 subjects were evaluated. The ADC map was calculated by using DWI with b = 10 and 300 s/mm². In those LNs where the LN hilum could be recognized, the LN ADC was measured with and without inclusion of the hilum, and the mean difference of the resulting ADC values was determined. RESULTS: The hilar structure was identified by DWI in 15 LNs. The ADC of the hilum was 1.981 ± 0.331 × 10⁻³ mm²/s. In these 15 LNs, the ADC value excluding hilar structure was significantly lower than the ADC value including hilar structure (0.983 ± 0.169 versus 1.206 ± 0.244 × 10⁻³ mm²/s; P < .0001). The mean ADC in a total of 58 LNs excluding the hilar structure was significantly lower than the value obtained including the hilar structure (1.034 ± 0.183 versus 1.095 ± 0.213 × 10⁻³ mm²/s; P = .0002). CONCLUSIONS: HR-DWI of neck LNs obtained by using 2D-ss-IMIV-DWEPI could identify the hilar structure. The ADC of normal neck LNs seemed significantly different when the hilum was included. The results suggest that HR-DWI may be helpful to aid selection of proper ROIs within LNs for accurate and reliable ADC measurements.

Quantification of diffusivities of the human cervical spinal cord using a 2D single-shot interleaved multisection inner volume diffusion-weighted echo-planar imaging technique.

BACKGROUND AND PURPOSE: DTI is a highly sensitive technique, which can detect pathology not otherwise noted with conventional imaging methods. This paper provides the atlas of reliable normative in vivo DTI parameters in the cervical spinal cord and its potential applications toward quantifying pathology. MATERIALS AND METHODS: In our study, we created a reference of normal diffusivities of the cervical spinal cord by using a 2D ss-IMIV-DWEPI technique from 14 healthy volunteers and compared parameters with those in 8 patients with CSM. The 2D ss-IMIV-DWEPI technique was applied in each subject to acquire diffusion-weighted images. FA, lambda( parallel), and lambda( perpendicular) were calculated. A reference of normal DTI indices from 12 regions of interest was created and compared with DTI indices of 8 patients. RESULTS: A map of reference diffusivity values was obtained from healthy controls. We found statistically significant differences in diffusivities between healthy volunteers and patients with CSM with different severities of disease, by using FA, lambda( parallel), and lambda( perpendicular) values. CONCLUSIONS: DTI using 2D ss-IMIV-DWPEI is sensitive to spinal cord pathology. This technique can be used to detect and quantify the degree of pathology within the cervical spinal cord from multiple disease states.

Diffusion tensor imaging of ex vivo cervical spinal cord specimens: the immediate and long-term effects of fixation on diffusivity.

Diffusion tensor imaging (DTI) is an emerging noninvasive method for evaluating tissue microstructure, but is highly susceptible to in vivo motion artifact. Ex vivo experiments on fixed tissues are needed to improve DTI techniques, which require fixed tissue specimens. Several efforts have been made to study the effect of fixation on both human and mouse tissue, with varying results. Four human cervical cords and three segments of pig cervical spinal cord specimens were imaged both before and after tissue fixation using 3D multishot diffusion weighted imaging (ms-DWEPI). Fixation caused a significant decrease in the longitudinal diffusivity whereas the relative anisotropy (RA) and radial diffusivity remained unaffected. Additionally, once adequately preserved, the diffusivity parameters of fixed tissue remain constant over time. Fixation has important effects on the diffusivity of tissue specimens. These findings have important implications for the determination of tissue microstructure and function using DTI technologies.

Influenza surveillance in Korea: establishment and first results of an epidemiological and virological surveillance scheme.

Surveillance is an important component of influenza control. This report describes the establishment and first results of the Korean Influenza Surveillance Scheme (KISS), an integrated clinical and laboratory surveillance network involving 622 public health centres (PHCs) and private clinics. Sentinel physicians reported cases of influenza-like illness (ILI) weekly and forwarded specimens for virus isolation and characterization. Influenza activity during the opening 2000-2001 season was milder and delayed compared with previous years. The ILI consultation rate corresponded well with the number of influenza virus isolates, both peaking in week 10 of 2001. Influenza A(H3N2) was the dominant isolate. The peak ILI consultation rate was higher in private clinics than in PHCs (5.04 vs 1.79 cases/1000 visits). An evaluation questionnaire generated potential enhancements to the scheme. KISS appears to represent the pattern of influenza activity accurately and will have a valuable role in monitoring and preventing epidemics in Korea.

Detection of hepatitis A virus from clotting factors implicated as a source of HAV infection among haemophilia patients in Korea.

To investigate the causal relationship of blood clotting factors and hepatitis A virus (HAV) infection in haemophilia patients during 1998-1999 in Korea, we performed a 1:3 matched case-control study and molecular detection of HAV from clotting factors and patients. The epidemiological investigation showed that one lot of clotting factor VIII was related epidemiologically to patients with hepatitis A with an odds ratio of 35.0, or 38.4 when adjusted for the interval between injections. We examined 17 sera collected from seven patients and 124 lots of blood clotting factors (factor VIII and factor IV) by HAV reverse transcriptase-polymerase chain reaction (RT-PCR). HAV RNA was detected in five clotting factors and six sera. The HAV sequence of one of the factor VIII samples was identical to the sequences found in three patients' sera. Findings from the laboratory and epidemiological studies suggested that the clotting factor was causally related to HAV infection in three haemophilia patients.

Improved accuracy and consistency in T1 measurement of flowing blood by using inversion recovery GE-EPI.

Problems associated with techniques currently used to measure the T1 of flowing blood are evaluated and a method to improve the consistency and repeatability of measurements is presented. Similar to some currently used techniques, the pulse sequence employs a nonselective adiabatic inversion pulse followed by a series of ECG-gated gradient echo EPI (echo planar imaging) images to obtain images where the blood (fluid) signal exhibits a T1-dependent inversion recovery signal from which the spin lattice relaxation constant (T1) of the flowing fluid can be measured. The new method combines curve fitting with a measure of the curve null point to acquire more accurate and consistent T1 values. Simulation and experimental results show that this combined fitting-nulling method is more stable and consistent in measuring the T1 of flowing fluid. The feasibility of temperature measurement of a flowing fluid based on the temperature dependence of the T1 of water protons is shown in this paper. ECG gating is used to reduce the effects of cyclic intensity changes for measurement of T1 in pulsatile flowing blood.

Temporal changes in reversible cerebral ischemia on perfusion- and diffusion-weighted magnetic resonance imaging: the value of relative cerebral blood volume maps.

Using a transorbital approach we induced the temporal occlusion and reperfusion model in 18 cats. A vascular clamp was placed on the main trunk of the left middle cerebral artery (MCA) for 1 h. Diffusion- and perfusion-weighted MR images were obtained at 1, 3, 6 and 24 h after the clip was released. The cats were killed 24 h after reperfusion, and triphenyl tetrazolium chloride (TTC) staining was performed. After the relative cerebral blood volume (rCBV), time to peak enhancement (TTP) and apparent diffusion coefficient (ADC) maps had been acquired, ROIs were drawn on (1) the area of the infarct produced, (2) the area of high signal intensity on initial diffusion-weighted magnetic resonance imaging (DWI) but normal on TTC staining, e.g., salvaged parenchyma. The ratios of these areas to the normal contralateral cortex were calculated and compared with those of the areas of the final infarct and the salvaged parenchyma. Areas of final infarct showed a temporal increase of rCBV on 3 and 6-h imaging and a final depletion on 24-h imaging. A persistent decrease of ADC value and delayed TTP were observed. Salvaged parenchyma also showed increased rCBV after reperfusion until the last imaging comparing it to the final area of infarct (P < 0.05, 24-h rCBV). The initial decrease in the ADC and delayed TTP normalized on 24-h imaging. In conclusion, rCBV of 24-h imaging was the reliable parameter to predict final infarct. A combination of serial changes on DWI and perfusion-weighted imaging (PWI) can predict ischemic penumbra and outcome.

Magnetic resonance imaging of articular cartilage.

Recent advances in treatments of the cartilage abnormalities require more information on the extent and shape of cartilage abnormalities and need for early detection of the lesions. In this article we review MR appearance of the cartilage correlated with histology, MR-related artifacts for cartilage imaging, conventional and dedicated MR techniques suitable for the cartilage, and their clinical utilization.

Transient MR signal changes in patients with generalized tonicoclonic seizure or status epilepticus: periictal diffusion-weighted imaging.

BACKGROUND AND PURPOSE: Our purpose was to investigate transient MR signal changes on periictal MR images of patients with generalized tonicoclonic seizure or status epilepticus and to evaluate the clinical significance of these findings for differential diagnosis and understanding of the pathophysiology of seizure-induced brain changes. METHODS: Eight patients with MR images that were obtained within 3 days after the onset of generalized tonicoclonic seizure or status epilepticus and that showed seizure-related MR signal changes had their records retrospectively reviewed. T1- and T2-weighted images were obtained of all eight patients. Additional diffusion-weighted images were obtained of five patients during initial examination. After adequate control of the seizure was achieved, follow-up MR imaging was performed. We evaluated the signal changes, location of the lesions, and degree of contrast enhancement on T1- and T2-weighted images and the signal change and apparent diffusion coefficient (ADC) on diffusion-weighted images. We also compared the signal changes of the initial MR images to those of the follow-up MR images. RESULTS: The initial MR images revealed focally increased T2 signal intensity, swelling, and increased volume of the involved cortical gyrus in all eight patients. The lesions were located in the cortical gray matter or subcortical white matter in seven patients and at the right hippocampus in one. T1-weighted images showed decreased signal intensity at exactly the same location (n = 6) and gyral contrast enhancement (n = 4). Diffusion-weighted images revealed increased signal intensity at the same location and focally reduced ADC. The ADC values were reduced by 6% to 28% compared with either the normal structure opposite the lesion or normal control. Follow-up MR imaging revealed the complete resolution of the abnormal T2 signal change and swelling in five patients, whereas resolution of the swelling with residual increased T2 signal intensity at the ipsilateral hippocampus was observed in the other two patients. For one of the two patients, hippocampal sclerosis was diagnosed. For the remaining one patient, newly developed increased T2 signal intensity was shown. CONCLUSION: The MR signal changes that occur after generalized tonicoclonic seizure or status epilepticus are transient increase of signal intensity and swelling at the cortical gray matter, subcortical white matter, or hippocampus on periictal T2-weighted and diffusion-weighted images. These findings reflect transient cytotoxic and vasogenic edema induced by seizure. The reversibility and typical location of lesions can help exclude the epileptogenic structural lesions.

Diffusion-weighted image and MR spectroscopic analysis of a case of MELAS with repeated attacks.

We report the clinical and MR manifestations of an 18 year-old girl with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome. Recurrent status epilepticus caused reversible cytotoxic edema on diffusion-weighted images (DWI). Initial and one month follow-up MR spectroscopy, after seizure control, showed some discrepancies in the ratio of metabolites. N-acetylaspartate (NAA) partially recovered (NAA/creatine (Cr) ratio: 1.27-->1.84). This was because of a normalization of decreased NAA due to cellular dysfunction as a result of status epilepticus. A low ratio of NAA/Cr due to abnormal mitochondria remained in the decreased state. Reversible NAA/Cr ratios in the acute lesion suggested that NAA reflects the neuronal function as well as the level of neuronal structural damage. The altered NAA/Cr ratio better correlated with the abnormal signal intensity area of T2-weighted images (T2WI) and DWI than the lactate (Lac)/Cr ratio. With conservative treatment with anti-epileptics not accompanied by coenzyme Q or sodium dichloroacetate, lactate persistently increased (Lac/Cr ratio: 1.01-->1.21) because of the continued production of lactate in cells with respiratory deficiency, which is the main pathology of MELAS.

Role of the inflamed synovial volume of the wrist in defining remission of rheumatoid arthritis with gadolinium-enhanced 3D-SPGR MR imaging.

The purpose of this study was to assess the role of inflamed synovial volume (ISV) in defining a state of remission in rheumatoid arthritis (RA) with contrast-enhanced, fat-suppression, three-dimensional (3D) gradient-recalled acquisition in the steady state with radiofrequency spoiling (SPGR) magnetic resonance (MR) imaging. Sixteen patients with RA (5 remission and 11 non-remission patients) were enrolled in this study. Contrast-enhanced, fat-suppression, 3D-SPGR MR imaging was performed before (n = 12) and after (n = 16) a mean 17 months of disease-modifying antirheumatic drugs (DMARDs). ISV was calculated by using a segmentation method. Statistical analysis of changes in ISVs and residual ISVs between the remission and the non-remission groups was performed. Intra- and inter-observer reproducibility was tested. Residual ISVs and relative changes in ISVs were 3.23 +/- 1.84 cm(3) and 51.4% (range 47.6-55.2%) in the remission group and 6.26 +/- 2. 03 cm(3)and 31.4% (range -73.5-53.5%) in the non-remission group. Both values were significantly different between the two groups (P < 0.05 and 0.05, respectively). Volume measurement showed high reproducibility: Intra- and inter-observer mean percentage errors were 5.04, 7.06, and 5.09%, respectively. Residual ISVs and relative changes in ISVs measured by MR imaging may provide objective and quantitative parameters in defining a state of remission in RA after therapy; however, the clinical utility of these measurements remains to be verified. J. Magn. Reson. Imaging 1999;10:202-208.

Correlation of laminated MR appearance of articular cartilage with histology, ascertained by artificial landmarks on the cartilage.

The object of this study was to correlate the laminae of articular cartilage on magnetic resonance (MR) imaging with histologic layers. T1- and fast spin-echo T2-weighted images of articular cartilage with artificial landmarks were obtained under high gradient echo strength (25 mT/m) conditions and a voxel size of 78 x 156 x 2000 microm. Images were also obtained with a) changed frequency-encoding directions; b) changed readout gradient strength; and c) a varied number of phase-encoding steps. T2 mapping was performed with angular variations. Artificial landmarks allowed accurate comparison between the laminae on MR images and the histologic zones. No alterations of the laminae were noted by changing the frequency gradient direction. Altering readout gradient strengths did not show a difference in the thickness of the laminae, and increasing the phase-encoding steps resulted in a more distinct laminated appearance, ruling out chemical shift, susceptibility, and truncation artifacts. The T2 mapping profile showed an anisotropic angular dependency from the magic angle effect. In conclusion, the laminated appearance of articular cartilage on spin-echo and fast spin-echo MR images correlated with the histologic zones rather than MR artifacts.

Minimizing artifacts caused by metallic implants at MR imaging: experimental and clinical studies.

OBJECTIVE: The purpose of this study was to investigate the effect of metallic implant positioning on MR imaging artifacts, to determine the optimal imaging conditions for minimizing artifacts, and to show the usefulness of artifact-minimizing methods in imaging of the knee. MATERIALS AND METHODS: Using MR images of experimental phantoms (titanium alloy and stainless steel screws), we compared the magnitude of metal-induced artifacts for various pulse sequences, different imaging parameters for the fast spin-echo sequence, and different imaging parameters for several incremental angles between the long axis of the screw and the direction of the main magnetic field. In clinical MR imaging of knees with metallic implants (n = 19), we assessed geometric distortion of anatomic structures to compare the influence of different pulse sequences (n = 19), frequency-encoding directions (n = 7), and knee positions (n = 15). RESULTS: Titanium alloy screws consistently produced smaller artifacts than did stainless steel screws. In experimental MR studies, artifacts were reduced with fast spin-echo sequences, with a screw orientation as closely parallel to the main magnetic field as possible, and, particularly, with smaller voxels that correlated positively with artifact size (R2 = .88, p < .01). In clinical MR studies, fast spin-echo MR imaging obscured articular structures less than did spin-echo imaging (8/19 patients). In particular, the anterior-posterior frequency-encoding direction (3/7 patients) and the flexion position of the knee (5/15 patients) were effective in reducing artifacts. CONCLUSION: MR artifacts can be minimized by optimally positioning in the magnet subjects with metallic implants and by choosing fast spin-echo sequences with an anterior-posterior frequency-encoding direction and the smallest voxel size.

Comparison of multishot turbo spin echo and HASTE sequences for T2-weighted MRI of liver lesions.

The purpose of this study was to compare the relative usefulness of multishot turbo spin echo (TSE) and half-Fourier single-shot turbo spin echo (HASTE) for determination of optimal breath-hold fast T2-weighted technique in terms of lesion detection, lesion-to-liver contrast-to-noise ratio (CNR), and image quality. The images of TSE with and without fat suppression (FS) and of HASTE with and without FS were retrospectively reviewed for 49 patients with 128 lesions. Without FS, TSE and HASTE images allowed depiction of focal hepatic masses (112 of 128, sensitivity = 87.5%) at the same rate. TSE with FS depicted more focal lesions (115 of 128, 89.8%) than HASTE with FS (109 of 128, 85.2%), but the difference was not statistically significant (P > .05). The CNR of each lesion on HASTE sequences was greater (P < .01) than that on TSE sequences. The CNR of hemangioma was distinct from that of solid tumors and cystic lesions in all sequences, and the range of CNR in each group of pathologies overlapped less and were well separated in the HASTE sequences. HASTE sequences produced better image quality with fewer artifacts (P < .0001). The results of this study suggest that HASTE sequences allow differentiation between solid tumors, hemangiomas, and cystic lesions in terms of CNR, producing fewer image artifacts, with acceptable sensitivity in lesion detection.