Biomedical subjects

T Namimoto

Publications and source records attributed to T Namimoto.

30 records · Page 2Linked to original sources

PubMedDate not supplied

Characterization of focal liver lesions with half-fourier acquisition single-shot turbo-spin-echo (HASTE) and inversion recovery (IR)-HASTE sequences.

The half-Fourier acquisition single-shot turbo-spin-echo (HASTE) sequence allows for heavily T2-weighted images, and the inversion recovery (IR)-HASTE sequence represents the T1 value of the tissue in a very short time. This study was undertaken to determine whether characterizing focal liver lesions can be made by combination with these very fast sequences. Seventy-four patients (33 cysts, 28 hemangiomas, and 33 malignant solid liver masses [15 metastatic tumors, 14 hepatocellular carcinomas, and 4 cholangiocarcinomas) underwent dynamic CT and breath-hold abdominal MRI using turbo-spin-echo (TSE), HASTE, and IR-HASTE sequences with variable T1 values on a 1.5-T MR unit. The imaging time for each slice was 2 seconds for HASTE imaging and 2 to 4 seconds for IR-HASTE imaging. Lesion detection and qualitative characterization were evaluated. Quantitative analysis was performed by measuring the contrast-to-noise ratios (CNRs) as well as visual analysis. The inversion time (TI) nulling values were also statistically analyzed. All cystic lesions were detected on both TSE and HASTE imagings. For solid lesions, TSE failed to detect one small solid lesion and HASTE sequence failed to detect three lesions. With HASTE sequences, all cysts and hemangiomas were markedly hyperintense in comparison with malignant solid masses. CNRs of hemangiomas or cysts were significantly higher than those of malignant solid masses (P < .01), and there was no overlap. The TI nulling value was 1,100+/-100 msec for hemangiomas, 1,900+/-110 msec for cysts, and 740+/-140 msec for malignant solid masses. There was no overlap between the TI nulling values of hemangiomas and cysts (P < .01). By combining the CNR from the HASTE sequence and the TI nulling value from the IR-HASTE sequence, complete discrimination among malignant solid masses, hemangiomas, and cysts of the liver could be made. Application of HASTE (representing T2 values) and IR-HASTE (representing T1 values) sequences provided a rapid and reliable imaging method for characterizing focal liver lesions without the use of contrast medium.

Adolescent↗

PubMedDate not supplied

The value of respiratory triggered T2-weighted turbo spin-echo imaging of the liver using a phased array coil.

The purpose of this study was to evaluate the value of the respiratory triggered turbo spin-echo (TSE) technique for T2-weighted MRI of liver lesions. Fifty-nine patients (32 men, 27 women; mean age, 63.3 years) with focal hepatic lesions were prospectively studied with MRI at 1.5 T with use of a body phased array coil. In the first 15 patients, breath-hold TSE, respiratory triggered TSE, and conventional nonrespiratory triggered TSE T2-weighted imaging were compared. Because nonrespiratory triggered TSE imaging was significantly inferior (P < .01) to breath-hold or respiratory triggered images, breath-hold and respiratory triggered TSE T2-weighted images were compared in the remaining 44 patients. Images were analyzed quantitatively by measuring the liver signal-to-noise ratio and the lesion-liver and spleen-liver contrast-to-noise ratios and qualitatively by evaluating the lesion conspicuity, liver parenchymal homogeneity, and sharpness of intrahepatic vessels. The imaging time was 26 seconds for breath-hold TSE imaging, 49 to 219 seconds (mean, 149 seconds) for the respiratory triggered TSE imaging, and 79 to 379 seconds (mean, 239 seconds) for the nonrespiratory triggered TSE imaging. Quantitatively, the signal-to-noise ratio of the liver for breath-hold imaging was comparable to that for respiratory triggered imaging. The lesion-liver and liver-spleen contrast-to-noise ratios for the respiratory triggered images were greater by 37% and 39%, respectively, than for the breath-hold T2-weighted TSE images. Qualitatively, the respiratory triggered images showed lower frequency of image artifact, better lesion conspicuity, and greatly superior depiction of intrahepatic structures compared with the breath-hold T2-weighted TSE images. The respiratory triggered T2-weighted TSE technique provides better quality liver images than the breath-hold TSE technique or nonrespiratory triggered technique within a reasonable acquisition time.

Adolescent↗

PubMedDate not supplied

Congenital anomalies of the pancreaticobiliary tract: findings on MR cholangiopancreatography (MRCP) using half-Fourier-acquisition single-shot turbo spin-echo sequence (HASTE).

The clinical significance of magnetic resonance cholangiopancreatography (MRCP) using half-Fourier acquisition single-shot turbo spin-echo (HASTE) in the evaluation of congenital anomalies of pancreaticobiliary tract was demonstrated in 56 patients (man: 31, women: 25; age: 0-60 years old, mean 15 years old) with suspected congenital anomalies of pancreaticobiliary tract. The image quality and characteristics were assessed. MRCP using HASTE with a phased array coil can be used as a non-invasive method for the evaluation of congenital anomalies of the pancreaticobiliary tracts.

Adolescent↗

PubMedDate not supplied

The value of dynamic MR imaging for hypointensity lesions of the peripheral zone of the prostate.

The aim was to evaluate the role of dynamic magnetic resonance (MR) imaging for prostatic carcinoma. Forty-two men with clinical suspicion of a prostatic carcinoma underwent MR imaging. Dynamic MR was performed, followed by postcontrast T1-weighted imaging with fat suppression. Histologic diagnosis was 21 prostatic carcinomas (in 19 patients), 21 benign tissues, and 2 chronic prostatitis. The diagnostic accuracy was 75% for T2-weighted images, and 79% for dynamic images. The accuracy of the combination of dynamic MR images with postcontrast T1-weighted images was 82%. It was concluded that dynamic MR imaging was useful in differentiation of low intensity lesions in the peripheral zone.

Aged↗

PubMedDate not supplied

High resolution breath-holding MR imaging of the abdomen with a phased-array multicoil.

We prospectively compared standard resolution and high resolution breath-hold T1- and T2-weighted images of the upper abdomen with use of a body phased-array multicoil in 30 patients. The image quality of high resolution T1-weighted FLASH sequence was equal to that of standard resolution sequence, while the quality of high resolution T2-weighted turbo spin-echo sequence was slightly inferior to that of standard resolution sequence. The merit of high resolution image is appreciated especially on a T1-weighted FLASH sequence.

Abdomen↗

PubMedDate not supplied

Experimental study on HASTE sequences: impacts of parameters on liver imaging.

This study investigates the impacts of effective TE (TEeff), echo spacing and echo train lengths (ETLs) on the imaging quality of HASTE sequences for liver imaging through a slit and a liver phantom. The HASTE sequence with a short echo spacing demonstrated higher CNR for a phantom simulating hepatocellular carcinoma (HCC) than that with long echo spacing. With a long echo spacing, the HASTE sequence showed higher spatial resolution for hemangiomas and metastasis. The improvement of spatial resolution along with the increase in ETLs (imaging matrix) was more prominent for hemangioma than for HCC.

Carcinoma, Hepatocellular↗

PubMedDate not supplied

Spin-echo echo-planar MR imaging of hepatocellular carcinoma arising from chronic liver damage: comparison with turbo spin-echo imaging.

The aim of this work was to evaluate the value of echo-planar imaging (EPI) in the detection of hepatocellular carcinomas arising in a chronic liver damage to respiratory triggered turbo spin-echo (TSE) imaging. With spin-echo EPI sequences, better lesion-liver contrast was obtained than TSE imaging. Although severe artifact is seen, this imaging produce good contrast, and may be useful as an adjunct to TSE imaging in evaluating patients with chronic liver damage.

Adolescent↗

PubMedDate not supplied

Diffuse perfusion abnormality of the liver parenchyma on angiography-assisted helical CT in relation to cirrhosis and previous treatments: a potential diagnostic pitfall for detecting hepatocellular carcinoma.

We evaluated diffuse perfusion abnormality of the liver parenchyma in relation to cirrhosis and previous treatments and estimated its potential limitation in detecting hepatocellular carcinomas (HCCs) on CT arterial portography (CTAP) and CT hepatic arteriography (CTHA). Sixty-one patients of liver cirrhosis with or without HCC received both CTAP and CTHA. Irregular defects of enhancement of the liver parenchyma on CTAP were noted in 37 of 61 patients (60.7%) and compensatory arterial perfusion in these defects on CTHA was noted in 30 of 37 patients (81.1%). Most patients had segmental or mixed patterns of enhancement. In patients with severe cirrhosis, irregular enhancement was often noted. The irregularity was also more often in patients who had had previous treatments. Four of 40 HCC nodules in 18 patients with severe irregular perfusion were not detected on CTAP and CTHA. Diffuse perfusion abnormalities of the liver parenchyma on CTAP and CTHA would decrease the accuracy of tumor detection in HCC patients.

Aged↗

PubMedDate not supplied

Fast breath-hold T2-weighted MRI of the kidney by means of half-Fourier single-shot turbo spin echo: comparison with high resolution turbo spin echo sequence.

PURPOSE: The value of the fast half-Fourier single-shot turbo spin echo (HASTE) sequence in T2-weighted MRI of the kidney was evaluated as a substitute for the conventional turbo spin echo (TSE) sequence. METHOD: Forty-five patients with suspected abnormalities of the kidney underwent MRI with a 1.5 T system. Breath-hold HASTE and respiratory-triggered TSE sequences were performed. Qualitative and quantitative analyses were performed for comparison of these sequences. RESULTS: The signal-to-noise ratio (SNR) with HASTE was higher than that with TSE. The lesion-to-kidney contrast-to-noise ratio for solid masses with HASTE was almost equal to that with TSE. For cystic masses, the CNR with HASTE was significantly higher than that with TSE (p < 0.05). Respiratory and chemical shift artifacts were significantly smaller on HASTE than on TSE (p < 0.01). However, the blurring artifact was higher on HASTE than on TSE (p = 0.01). CONCLUSION: The HASTE sequence generates high contrast images and is free of motion and chemical shift artifacts, with much better time efficacy. The sequence provides comparable diagnostic information to TSE sequences.

Adult↗

PubMedDate not supplied

Metastatic liver tumor from cystic ovarian carcinomas: CT and MRI appearance.

OBJECTIVE: The initial and follow-up CT and MRI images of ten patients with hepatic metastases from ovarian tumors were retrospectively analyzed to establish their features and sequential changes in appearance. MATERIALS AND METHODS: Ten patients with hepatic metastasis from ovarian tumors received initial and follow-up CT and MRI examinations. Six patients were followed up every two to three weeks before surgical tumor resection. Both CT and MR images were analyzed by two radiologists. RESULTS: A total of fourteen lesions were detected by CT and MRI in 10 patients. All 14 lesions were demonstrated as areas of marked hyperintensity on T2-weighted MRI. Eleven cyst-like tumors were demonstrated as round or oval low density lesions on CT and as areas of hypointensity on T1-weighted imaging. Three lesions were shown as solid masses with slightly low attenuation at the initial CT examination and slightly low or iso-intensity areas on T1-weighted imaging, and these lesions showed early peripheral globular enhancement and delayed enhancement on contrast-enhanced CT and MR imaging. Cystic formation was observed two to three weeks later after initial study in all the 3 solid lesions. Rapid subcapsular effusion, which showed obvious enhancement on delayed Gd-DTPA enhanced MR imaging, was observed in two patients. CONCLUSION: The hepatic metastatic tumor from cystic ovarian carcinoma may manifest as a well-defined cystic lesion or as a solid mass, and the solid mass shows delayed enhancement on contrast-enhanced CT and MR imaging. Furthermore, rapid cystic formation and rapid subcapsular extension is frequently seen.

Adult↗

PubMedDate not supplied

Calculation of T2 relaxation time from ultrafast single shot sequences for differentiation of liver tumors: comparison of echo-planar, HASTE, and spin-echo sequences.

PURPOSE: The purpose of this study was to evaluate the accuracy of T2 calculation from single shot imaging sequences such as echo-planar imaging (EPI) and half-Fourier single shot turbo spin-echo (HASTE) imaging. MATERIALS AND METHODS: For the phantom study, we prepared vials containing different concentrations of agarose, copper sulfate, and nickel chloride. The temperature of the phantom was kept at 22 degrees C. MR images were obtained with a 1.5-Tesla superconductive magnet. Spin-echo (SE) -type EPI and HASTE sequences with different TEs were obtained for T2 calculation, and the T2 values were compared with those obtained from the Carr-Purcell-Meiborm-Gill (CPMG) sequence. The clinical study group consisted of 30 consecutive patients referred for MR imaging to characterize focal liver lesions. A total of 40 focal liver lesions were evaluated, including 25 primary or metastatic solid masses and 15 non-solid lesions. Single shot SE-type EPI and HASTE were both performed with TEs of 64 and 90 msec. RESULTS: In the phantom study, the T2 values obtained from both single shot sequences showed significant correlations with those from the CPMG sequence (T2 on EPI vs. T2 on CPMG: r=0.98, p<0.01; T2 on HASTE vs. T2 on CPMG: r=0.99, p<0.01). In the clinical study, mean T2 values for liver calculated from EPI (42 msec) were significantly shorter than those calculated from the HASTE sequence (58 msec) (p<0.001). Mean T2 values for solid tumors were 95 msec with HASTE and 72 msec with EPI, and mean T2 values for non-solid lesions were 128 msec with HASTE and 159 msec with EPI. Although mean T2 values between solid and non-solid lesions were significantly different for both EPI and HASTE sequences (p=0.01 for HASTE, p<0.001 for EPI), the overlap of solid and non-solid lesions was less frequent in EPI than in HASTE. CONCLUSION: With single shot sequences, it is possible to obtain the T2 values that show excellent correlation with the CPMG sequence. Although both HASTE and EPI are useful to calculate T2 values, EPI appears to be more accurate in characterizing focal liver lesions.

Adult↗

PubMedDate not supplied

The value of fast and ultrafast T2-weighted MR imaging sequences in hepatic enhancement with ferumoxides: comparison with conventional spin-echo sequence.

PURPOSE: The efficacy of superparamagnetic iron oxide (SPIO) was evaluated with fast T2-weighted imaging sequences such as turbo spin-echo (TSE), half-Fourier single shot turbo spin echo (HASTE), and echo-planar imaging (EPI) in comparison with the conventional spin-echo (SE) sequence on a 1.5 Tesla MR unit. MATERIALS AND METHODS: In a phantom study, we prepared vials containing different concentrations of ferumoxides (0, 0.25, 0.5, 0.75, and 1 micromol Fe) in 2% agarose simulating the liver. In an animal study, contrast medium in doses of 10, 20, and 30 micromol/kg of ferumoxides was injected into the ear vein of rabbits weighing 3.0-4.0 kg under general anesthesia. MR imaging of the phantom and liver of the rabbits was obtained with the T2-weighted SE sequence (TR/TE=2000/20, 80), TSE sequences (TR/effective TE=2000/90, echo train length=7), HASTE (effective TE=64, 90 msec), and EPI (effective TE=64, 90 msec). Three rabbits in each group were imaged before and 1 hour after ferumoxides administration for in-vivo study. The Signal intensity of pre- and postcontrast imaging of the phantom or rabbits' livers was measured with operator-defined regions of interest, and signal-to-noise ratios (SNR) were obtained. Immediately after imaging, the rabbits were sacrificed and the livers were removed at autopsy, followed by ex-vivo study. In a clinical study, 10 micromol/kg of ferumoxides was given in 34 consecutive patients with 31 solid tumors. The liver SNR were evaluated for all 34 patients, and tumor to-liver contrast-to-noise ratios (CNR) were evaluated for all 31 solid lesions. The same series of imaging techniques as in the experimental studies was performed for quantitative and qualitative analyses. RESULTS: In both in-vitro and in-vivo studies, SNR of the phantom or rabbits' livers significantly decreased after ferumoxides administration. The decrease in SNR on excised rabbits' livers was 72% for EPI, 36% for HASTE, 61% for SE, and 51% for TSE at a dose of 10 micromol/kg of ferumoxides. In the clinical study, HASTE and TSE showed significant improvement in CNRs after ferumoxides administration (p<0.05). Visual analysis revealed improvement in tumor detection for all sequences. On EPI, although contrast was excellent, severe image distortion was seen. Although the signal decrease with HASTE and TSE was somewhat inferior to those with EPI and SE, respectively, the effect of contrast enhancement on HASTE and TSE was marked on visual analysis. CONCLUSION: Although TSE sequences and HASTE sequences are less susceptible to magnetic field inhomogeneities than SE and EPI sequences, the decrease in liver signal on HASTE and TSE sequences was comparable to that on EPI and SE sequences, respectively. These sequences are useful clinically for ferumoxides imaging, because they are less sensitive to motion artifacts.

Adult↗