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Image Denoising for Metal MRI Exploiting Sparsity and Low Rank Priors.

Sangcheon CHOI ; Jun Sik PARK ; Hahnsung KIM ; Jaeseok PARK

Investigative Magnetic Resonance Imaging.2016;20(4):215-223. doi:10.13104/imri.2016.20.4.215

PURPOSE: The management of metal-induced field inhomogeneities is one of the major concerns of distortion-free magnetic resonance images near metallic implants. The recently proposed method called “Slice Encoding for Metal Artifact Correction (SEMAC)” is an effective spin echo pulse sequence of magnetic resonance imaging (MRI) near metallic implants. However, as SEMAC uses the noisy resolved data elements, SEMAC images can have a major problem for improving the signal-to-noise ratio (SNR) without compromising the correction of metal artifacts. To address that issue, this paper presents a novel reconstruction technique for providing an improvement of the SNR in SEMAC images without sacrificing the correction of metal artifacts. MATERIALS AND METHODS: Low-rank approximation in each coil image is first performed to suppress the noise in the slice direction, because the signal is highly correlated between SEMAC-encoded slices. Secondly, SEMAC images are reconstructed by the best linear unbiased estimator (BLUE), also known as Gauss-Markov or weighted least squares. Noise levels and correlation in the receiver channels are considered for the sake of SNR optimization. To this end, since distorted excitation profiles are sparse, l1 minimization performs well in recovering the sparse distorted excitation profiles and the sparse modeling of our approach offers excellent correction of metal-induced distortions. RESULTS: Three images reconstructed using SEMAC, SEMAC with the conventional two-step noise reduction, and the proposed image denoising for metal MRI exploiting sparsity and low rank approximation algorithm were compared. The proposed algorithm outperformed two methods and produced 119% SNR better than SEMAC and 89% SNR better than SEMAC with the conventional two-step noise reduction. CONCLUSION: We successfully demonstrated that the proposed, novel algorithm for SEMAC, if compared with conventional de-noising methods, substantially improves SNR and reduces artifacts.
Artifacts ; Least-Squares Analysis ; Magnetic Resonance Imaging* ; Methods ; Noise ; Signal-To-Noise Ratio

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Effect of Number of Measurement Points on Accuracy of Muscle T2 Calculations.

Noriyuki TAWARA ; Atsushi NISHIYAMA

Investigative Magnetic Resonance Imaging.2016;20(4):207-214. doi:10.13104/imri.2016.20.4.207

PURPOSE: The purpose of this study was to investigate the effect of the number of measurement points on the calculation of transverse relaxation time (T2) with a focus on muscle T2. MATERIALS AND METHODS: This study assumed that muscle T2 was comprised of a single component. Two phantom types were measured, 1 each for long (“phantom”) and short T2 (“polyvinyl alcohol gel”). Right calf muscle T2 measurements were conducted in 9 healthy male volunteers using multiple-spin-echo magnetic resonance imaging. For phantoms and muscle (medial gastrocnemius), 5 regions of interests were selected. All region of interest values were expressed as the mean ± standard deviation. The T2 effective signal-ratio characteristics were used as an index to evaluate the magnetic resonance image quality for the calculation of T2 from T2-weighted images. The T2 accuracy was evaluated to determine the T2 reproducibility and the goodness-of-fit from the probability Q. RESULTS: For the phantom and polyvinyl alcohol gel, the standard deviation of the magnetic resonance image signal at each echo time was narrow and mono-exponential, which caused large variations in the muscle T2 decay curves. The T2 effective signal-ratio change varied with T2, with the greatest decreases apparent for a short T2. There were no significant differences in T2 reproducibility when > 3 measurement points were used. There were no significant differences in goodness-of-fit when > 6 measurement points were used. Although the measurement point evaluations were stable when > 3 measurement points were used, calculation of T2 using 4 measurement points had the highest accuracy according to the goodness-of-fit. Even if the number of measurement points was increased, there was little improvement in the probability Q. CONCLUSION: Four measurement points gave excellent reproducibility and goodness-of-fit when muscle T2 was considered mono-exponential.
Humans ; Magnetic Resonance Imaging ; Male ; Muscle, Skeletal ; Polyvinyl Alcohol ; Relaxation ; Volunteers

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Detection of Perivalvular Abscess with Late Gadolinium-Enhanced MR Imaging in a Patient with Infective Endocarditis.

Seong Yoon RYU ; Hae Jin KIM ; Sung Mok KIM ; Sung Ji PARK ; Yeon Hyeon CHOE

Investigative Magnetic Resonance Imaging.2016;20(1):75-79. doi:10.13104/imri.2016.20.1.75

We report a case of perivalvular abscess in a 66-year-old man with infective endocarditis, diagnosed by late gadolinium-enhanced (LGE) cardiovascular magnetic resonance (CMR) imaging. No clinical features suspicious of infective endocarditis were noted, however, transthoracic echocardiography revealed non-specific echogenic focal wall thickening at mitral-aortic intervalvular fibrosa. Perivalvular abscess in the aortic valve was demonstrated as focal wall thickening between the anterior mitral leaflet and the non-coronary cusp of the aortic valve with peripheral enhancement and central low signal intensity on LGE CMR imaging. Other features suggestive of infective endocarditis, such as neither vegetation nor valvular perforation were present. The perivalvular abscess did not grow after intensive intravenous antibiotics therapy, and the patient was discharged without surgical treatment. CMR with LGE provided an early accurate diagnosis of perivalvular abscess. The diagnosis of perivalvular abscess using LGE CMR imaging was not previously reported in Korea.
Abscess* ; Aged ; Anti-Bacterial Agents ; Aortic Valve ; Diagnosis ; Echocardiography ; Endocarditis* ; Humans ; Korea ; Magnetic Resonance Imaging*

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Wernicke's Encephalopathy with Intracranial Hemorrhage.

Sunghee JEON ; Hyunkoo KANG

Investigative Magnetic Resonance Imaging.2016;20(1):71-74. doi:10.13104/imri.2016.20.1.71

Wernicke's encephalopathy (WE) is an acute neurological disorder resulting from thiamine deficiency. Early diagnosis and treatment of WE is important to avoid persistent brain damage. Although histopathologic examination usually demonstrates pin-point hemorrhages in affected brain parenchyma, secondary hemorrhage is a rare but serious complication of WE. We experienced a rare case of intracranial hemorrhage related to WE in a 56-year-old male patient with malnourishment.
Brain ; Early Diagnosis ; Hemorrhage ; Humans ; Intracranial Hemorrhages* ; Magnetic Resonance Imaging ; Male ; Middle Aged ; Nervous System Diseases ; Thiamine Deficiency ; Wernicke Encephalopathy*

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Mucoepidermoid Carcinoma with Distant Metastases to the Kidney, Adrenal Gland, Skull and Gluteus Maximus Muscle: a Case Report.

Sang Wook SON ; Kye Ho LEE ; Jai Hyuen LEE ; Na Hye MYONG ; Dong Soo YOO

Investigative Magnetic Resonance Imaging.2016;20(1):66-70. doi:10.13104/imri.2016.20.1.66

INTRODUCTION: Distant metastases of mucoepidermoid carcinoma (MEC) are reported with the most common sites being the soft tissue of skin, lung, liver, and bone. We report here a very rare case of MEC with multiple metastases to the kidney, adrenal gland, skull and gluteus maximus muscle. CASE REPORT: A 63-year-old male patient presented with left-sided headache. Radiologic evaluations including CT and MRI showed ill-defined soft tissue lesion involving the left infratemporal fossa and left sphenoid sinus, and multiple enlarged lymph nodes in neck and mediastinum. PET-CT demonstrated multiple hypermetabolic lesions in and around the left kidney, left adrenal gland, right ischium, right gluteus maximus and skull base. These lesions were confirmed as MEC with multiple metastases through biopsy. DISCUSSION: Only one case of metastasis to the skull has been previously reported, and moreover, there has not been a case of metastatic MEC to the kidney, adrenal gland and gluteus maximus muscle so far in the medical literature. It is important to acknowledge the possibility of every unusual MEC metastases, since the presence of metastasis has statistically significant influence on the survival of MEC.
Adrenal Glands* ; Biopsy ; Carcinoma, Mucoepidermoid* ; Headache ; Humans ; Ischium ; Kidney* ; Liver ; Lung ; Lymph Nodes ; Magnetic Resonance Imaging ; Male ; Mediastinum ; Middle Aged ; Neck ; Neoplasm Metastasis* ; Positron-Emission Tomography ; Skin ; Skull Base ; Skull* ; Sphenoid Sinus

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Subperiosteal Osteoid Osteoma of the Knee: Case Report.

Hie Bum SUH ; In Sook LEE ; Seung Joon RHEE ; You Seon SONG ; Jong Woon SONG

Investigative Magnetic Resonance Imaging.2016;20(1):61-65. doi:10.13104/imri.2016.20.1.61

Osteoid osteoma, a frequent lesions of bone, is usually intraosseous but occasionally subperiosteal. We describe the case of a 19-year-old male with knee pain caused by subperiosteal osteoid osteoma. Radiologic evaluation was performed with radiographic, computed tomography (CT), ultrasonographic (US) and magnetic resonance imaging (MRI). But the preoperative diagnosis of osteoid osteoma was delayed because of unusual imaging findings and atypical symptom. After excisional biopsy, histological examination confirmed the diagnosis of osteoid osteoma. The lesion was treated successfully with CT-guided radiofrequency ablation.
Biopsy ; Catheter Ablation ; Diagnosis ; Humans ; Knee* ; Magnetic Resonance Imaging ; Male ; Osteoma, Osteoid* ; Young Adult

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A Case of Widespread Cavernous Malformations of the Central Nervous System Associated with Acute Neurologic Deficit.

Kyung Chul NOH ; Sung Eun CHUNG ; Dokyung LEE

Investigative Magnetic Resonance Imaging.2017;21(1):34-37. doi:10.13104/imri.2017.21.1.34

A 45-year-old female visited our clinic due to sudden right leg weakness and sensory loss. Brain and spinal cord magnetic resonance imaging showed widespread cavernous malformations. Cavernous malformation in L1 spine area was accompanied by a subacute stage hematoma with perilesional edema. Sensory loss subsided after corticosteroid therapy. Usually, neurologic deficit by spinal cavernous malformation appears more chronically in the adults compared to children. Treatment options are difficult to establish in a case with multiple cavernous malformations. Identifying hemorrhagic lesions by extensive neuroimaging evaluation could be helpful to select the treatment target for cavernous malformation.
Adult ; Brain ; Central Nervous System* ; Child ; Edema ; Female ; Hematoma ; Hemorrhage ; Humans ; Leg ; Magnetic Resonance Imaging ; Middle Aged ; Neuroimaging ; Neurologic Manifestations* ; Spinal Cord ; Spine

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Measurement and Compensation of Respiration-Induced B0 Variations in Lumbar Spine Bone Marrow Fat Quantification.

Yoonho NAM ; Eojin HWANG ; Joon Yong JUNG

Investigative Magnetic Resonance Imaging.2017;21(1):28-33. doi:10.13104/imri.2017.21.1.28

PURPOSE: To investigate and compensate the effects of respiration-induced B0 variations on fat quantification of the bone marrow in the lumbar spine. MATERIALS AND METHODS: Multi-echo gradient echo images with navigator echoes were obtained from eight healthy volunteers at 3T clinical scanner. Using navigator echo data, respiration-induced B0 variations were measured and compensated. Fat fraction maps were estimated using T2*-IDEAL algorithm from the uncompensated and compensated images. For manually drawn bone marrow regions, the estimated B0 variations and the calculated fat fractions (before and after compensations) were analyzed. RESULTS: An increase of temporal B0 variations from inferior level to superior levels was observed for all subjects. After compensation using navigator echo data, the effects of the B0 variations were reduced in gradient echo images. The calculated fat fractions show significant differences (P < 0.05) in L1 and L3 between the uncompensated and the compensated. CONCLUSION: The results of this study raise the need for considering respiration-induced B0 variations for accurate fat quantification using gradient echo images in the lumbar spine. The use of navigator echo data can be an effective way for the reduction of the effects of respiratory motion on the quantification.
Bone Marrow* ; Compensation and Redress* ; Healthy Volunteers ; Respiration ; Spine*

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Assessment of Left Ventricular Function with Single Breath-Hold Magnetic Resonance Cine Imaging in Patients with Arrhythmia.

So Hyeon BAK ; Sung Mok KIM ; Sung Ji PARK ; Min Ji KIM ; Yeon Hyeon CHOE

Investigative Magnetic Resonance Imaging.2017;21(1):20-27. doi:10.13104/imri.2017.21.1.20

PURPOSE: To evaluate quantification results of single breath-hold (SBH) magnetic resonance (MR) cine imaging compared to results of conventional multiple breath-hold (MBH) technique for left ventricular (LV) function in patients with cardiac arrhythmia. MATERIALS AND METHODS: MR images of patients with arrhythmia who underwent MBH and SBH cine imaging at the same time on a 1.5T MR scanner were retrospectively reviewed. Both SBH and MBH cine imaging were performed with balanced steady state free precession. SBH scans were acquired using temporal parallel acquisition technique (TPAT). Fifty patients (65.4 ± 12.3 years, 72% men) were included. End-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), myocardial mass, and LV regional wall motion were evaluated. RESULTS: EF, myocardial mass, and regional wall motion were not significantly different between SBH and MBH acquisition techniques (all P-values > 0.05). EDV, ESV, and SV were significant difference between the two techniques. These parameters for SBH cine imaging with TPAT tended to lower than those in MBH. EF and myocardial mass of SBH cine imaging with TPAT showed good correlation with values of MBH cine imaging in Passing-Bablok regression charts and Bland-Altman plots. However, SBH imaging required significantly shorter acquisition time than MBH cine imaging (15 ± 7 sec vs. 293 ± 104 sec, P < 0.001). CONCLUSION: SBH cine imaging with TPAT permits shorter acquisition time with assessment results of global and regional LV function comparable to those with MBH cine imaging in patients with arrhythmia.
Arrhythmias, Cardiac* ; Humans ; Retrospective Studies ; Stroke Volume ; Ventricular Function, Left*

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Differentiation between Glioblastoma and Primary Central Nervous System Lymphoma Using Dynamic Susceptibility Contrast-Enhanced Perfusion MR Imaging: Comparison Study of the Manual versus Semiautomatic Segmentation Method.

Ye Eun KIM ; Seung Hong CHOI ; Soon Tae LEE ; Tae Min KIM ; Chul Kee PARK ; Sung Hye PARK ; Il Han KIM

Investigative Magnetic Resonance Imaging.2017;21(1):9-19. doi:10.13104/imri.2017.21.1.9

BACKGROUND: Normalized cerebral blood volume (nCBV) can be measured using manual or semiautomatic segmentation method. However, the difference in diagnostic performance on brain tumor differentiation between differently measured nCBV has not been evaluated. PURPOSE: To compare the diagnostic performance of manually obtained nCBV to that of semiautomatically obtained nCBV on glioblastoma (GBM) and primary central nervous system lymphoma (PCNSL) differentiation. MATERIALS AND METHODS: Histopathologically confirmed forty GBM and eleven PCNSL patients underwent 3T MR imaging with dynamic susceptibility contrast-enhanced perfusion MR imaging before any treatment or biopsy. Based on the contrast-enhanced T1-weighted imaging, the mean nCBV (mCBV) was measured using the manual method (manual mCBV), random regions of interest (ROIs) placement by the observer, or the semiautomatic segmentation method (semiautomatic mCBV). The volume of enhancing portion of the tumor was also measured during semiautomatic segmentation process. T-test, ROC curve analysis, Fisher's exact test and multivariate regression analysis were performed to compare the value and evaluate the diagnostic performance of each parameter. RESULTS: GBM showed a higher enhancing volume (P = 0.0307), a higher manual mCBV (P = 0.018) and a higher semiautomatic mCBV (P = 0.0111) than that of the PCNSL. Semiautomatic mCBV had the highest value (0.815) for the area under the curve (AUC), however, the AUCs of the three parameters were not significantly different from each other. The semiautomatic mCBV was the best independent predictor for the GBM and PCNSL differential diagnosis according to the stepwise multiple regression analysis. CONCLUSION: We found that the semiautomatic mCBV could be a better predictor than the manual mCBV for the GBM and PCNSL differentiation. We believe that the semiautomatic segmentation method can contribute to the advancement of perfusion based brain tumor evaluation.
Area Under Curve ; Biopsy ; Blood Volume ; Brain Neoplasms ; Central Nervous System* ; Diagnosis, Differential ; Glioblastoma* ; Humans ; Lymphoma* ; Magnetic Resonance Imaging* ; Methods* ; Perfusion* ; ROC Curve

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