Shigehide Kuhara

Method/apparatus for NMR imaging using an imaging scheme sensitive to inhomogeneity and a scheme insensitive to inhomogeneity in a single imaging step

A nuclear magnetic resonance imaging scheme for imaging living body information related to the physiological function change in the living body. In this scheme, the pulse sequence realizes a first imaging scheme sensitive to functional information of the body to be examined and a second imaging scheme insensitive to the functional information of the body to be examined so as to obtain first and second types of the nuclear magnetic resonance images corresponding to the first and second imaging schemes, respectively, by a single execution of this pulse sequence. The functional information of the body to be examined is then obtained by processing the first and second types of the nuclear magnetic resonance images.

Method and apparatus for high speed magnetic resonance imaging with improved image quality

A nuclear magnetic resonance imaging method and apparatus, capable of obtaining images with high spatial resolution arid S/N ratio, reducing the influence of the inhomogeneity of the static magnetic field and the chemical shift artifacts, and improving the contrast in the T2 enhanced image and T1 enhanced image. The imaging uses the pulse sequence, including: application of RF pulses and slicing gradient magnetic field for exciting a desired region of the body to be examined; application of reading gradient magnetic fields which regularly fluctuate between a negative value and a positive value; application of initial phase encoding gradient magnetic field before the reading gradient magnetic field is applied; application of a predetermined pulse shaped phase encoding gradient magnetic field every time the reading gradient magnetic field changes polarity; and collection of the echo signals emitted from the desired region every time the reading gradient magnetic field changes polarity. This pulse sequence is repeated while sequentially changing a setting of the initial phase encoding gradient magnetic field applied.

Nuclear magnetic resonance imaging with patient protection against nerve stimulation and image quality protection against artifacts

A nuclear magnetic resonance imaging scheme capable of reducing the eddy currents induced within the living body outside of the imaging region, so as to protect the patient against the nerve stimulation due to the eddy currents, and obtaining the MR images at high image quality by protecting the image quality against the N/2 and chemical artifacts. The nerve stimulation is prevented by providing a shield member for shielding a nerve stimulation sensitive portion of the patient located outside of the imaging region from a change of the gradient magnetic fields. The artifacts are prevented by applying a reading gradient magnetic field which is repeatedly switching its polarity along a phase encoding gradient magnetic field applied at a rate of once in every two switchings of the reading gradient magnetic field, separating the acquired NMR signals resulting from odd and even turns of switchings of the reading gradient magnetic field as separate data sets, and re-constructing MR images from the separate data set for odd turns and even turns separately.

Whole-heart coronary magnetic resonance angiography with parallel imaging: comparison of acceleration in one-dimension vs. two-dimensions.

PURPOSE To evaluate visualization of the whole-heart coronary arteries accelerated with parallel imaging (PI) applied in two-dimension (2D) in comparison with one-dimension (1D). MATERIALS AND METHODS Seventeen healthy subjects were studied with a 1.5-T scanner equipped with a whole body phased array coil system and 16-channel receivers. Using 16 coil elements, whole-heart coronary magnetic resonance angiography (CMRA) was acquired in two conditions of 1D-PI and 2D-PI. The former scan was accelerated in phase direction by factor of 2 and the latter in phase and slice directions by factors of 2.5 and 2, respectively. Visualized length of right coronary artery (RCA), left anterior descending artery (LAD), and left circumflex artery (LCX) was measured. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) was also measured. The CMRA quality was assessed in segment-wise with a five-point scale. RESULTS The average scan time decreased to 5.3+/-2.2 min in 2D-PI from 11.6+/-3.5 min in 1D-PI, reducing the scan time to 45%. The visualized length, SNR, and CNR in average were smaller for images of 2D-PI compared with those of 1D-PI, however, statistically significant results were observed only in RCA (P<0.05). Score reduction of 2D-PI image quality was limited to 0.34 in average, and only two out of fifteen segments (#2, 6) showed significant score deterioration (P<0.05). CONCLUSIONS Compared with the relatively limited degree of image degradation, 2D-PI offered a large reduction of the acquisition time, which is of large benefit in clinical situations.

Radiologist model for cardiac rest period determination based on fuzzy rule

Image data acquisition for the coronary arteries is generally implemented during the diastole rest period, in order to suppress blurring due to cardiac movement. The purpose of this study is to improve the semi-automated application to determine the cardiac rest period based on fuzzy logic. The cardiac rest period from 25 subjects were determined based on their normalized cross-correlation of consecutive frame images as well as normalized frame number as the measured variables. The fuzzy set and membership are generated based on the measured variables from the radiologists visual assessment. That visual assessment is also regarded as a gold standard for verification. The distance difference between the proposed method and visual assessment was analyzed. The fuzzy logic approach for cardiac rest period determination has no significant difference compared to the visual assessment (p>0.05) in terms of start frame and end frame. The algorithm could be extended easily in case of there are some necessary variables should be added to accommodate rest period definition from different radiologist.

Coronary Whole-heart MR Angiography: Feasibility of Breath-hold Chasing with Diaphragmatic Navigation

We propose a simple but novel data acquisition technique for whole-heart coronary magnetic resonance angiography (CMRA). In this technique, the breath-hold chasing MRA, data are collected during breath-hold intervals, with the navigation window manually adjusted to the diaphragmatic level. Compared with the conventional free breathing MRA, this method provided 33% reduction of acquisition time and improved visibility of right coronary artery in 18 normal subjects without any additional software or hardware requirements.

Clinical application of an automatic slice-alignment method for cardiac MR imaging.

PURPOSE We evaluated the usefulness of an automatic slice-alignment method to simplify planning of cardiac magnetic resonance (MR) scans with a 3-tesla scanner. METHODS We obtained 2-dimensional (2D) axial multislice images using steady-state free precession (SSFP) sequences covering the whole heart at the end-diastole phase with electrocardiography (ECG) gating in 38 patients. We detected several anatomical feature points of the heart and calculated all planes required for cardiac imaging based on those points. We visually evaluated the acceptability of an acquired imaging plane and measured the angular differences of each view between the results obtained by this method and by a conventional manual pointing approach. RESULTS The average visual scores were 3.4 ± 1.0 for short-axis images, 3.2 ± 0.9 for 4-chamber images, 3.2 ± 0.8 for 2-chamber images, and 3.3 ± 0.8 for 3-chamber images; average angular differences were 5.8 ± 5.1 (short axis), 7.7 ± 5.7 (4-chamber), 11.5 ± 6.7 (2-chamber), and 9.1 ± 4.6 degrees (3-chamber). Processing time was within 1.8 s in all subjects. CONCLUSION The proposed method can provide planes within the clinically acceptable range and within a short time in cardiac imaging of patients with various cardiac shapes and diseases without the need for high level operator proficiency in performing the examination and interpreting results.

Evaluation of clinical datasets in fully automatic planning assist system for cardiac magnetic resonance imaging.

Background Planning assist systems for cardiac MR examinations are necessary for easier operation and shorter examination times. Slice alignment systems [1] have played an important role in achieving these objectives. We propose a new automatic planning assist system for couch adjustment, local shimming, and axial multislice imaging as the input to a slice alignment system [2]. The new system employs an atlas-based segmentation technique using single scout volume data. In the present study, the accuracy and robustness of the proposed method were evaluated based on more than 50 datasets including clinical data, and the results were compared against the degree of interobserver error in manual annotation.

Whole-heart coronary MR angiography under a single breath-hold: A comparative study with respiratory-gated acquisition using a multi-element phased-array coil

AIM To compare visualization using whole-heart coronary magnetic resonance angiography (CMRA) acquired during a single breath-hold (BH) with that using conventional respiratory-gated (RG) CMRA. MATERIALS AND METHODS The CMRAs of 14 healthy subjects under either BH or RG conditions were studied using a 1.5 T system equipped with a whole-body phased-array coil and 16-channel receivers. The BH examination was accelerated using parallel imaging (PI) by factors of 2.5 and 2 in the phase and section directions, respectively. For the RG examination, a PI factor of 2 was used only in the phase direction. The visualization quality of 15 coronary segments using each condition was evaluated with a five-point scale (0-4). Differences between two conditions were compared at segments with an average score greater than 2 in RG-CMRA. RESULTS The average examination time for BH and RG acquisition scans was 34 s and 11 min 31 s, respectively. Ten segments (segments 1-3, 5-9, 11, and 13) had average scores higher than 2 in RG-CMRA. Of these, BH-CMRA had significantly lower scores than RG-CMRA at six segments (segments 1, 5-8, and 11) after correction for multiple comparisons (p<0.005). However, in BH-CMRA, proximal segments (segments 1-2, 5-7, and 11) showed average scores over 2, indicating marginally acceptable image quality. CONCLUSION Compared with the relatively limited degree of image degradation with RG-CMRA, the present data suggest that BH-CMRA would be useful for screening and as an adjunct to RG-CMRA that is occasionally incomplete.

Whole-heart magnetic resonance coronary angiography with multiple breath-holds and automatic breathing-level tracking

Whole-heart (WH) magnetic resonance coronary angiography (MRCA) studies are usually performed during free breathing while monitoring the position of the diaphragm with real-time motion correction. However, this results in a long scan time and the patient’s breathing pattern may change, causing the study to be aborted. Alternatively, WH MRCA can be performed with multiple breath-holds (mBH). However, one problem in the mBH method is that patients cannot hold their breath at the same position every time, leading to image degradation. We have developed a new WH MRCA imaging method that employs both the mBH method and automatic breathing-level tracking to permit automatic tracking of the changes in breathing or breath-hold levels. Evaluation of its effects on WH MRCA image quality showed that this method can provide high-quality images within a shorter scan time. This proposed method is expected to be very useful in clinical WH MRCA studies.