Objective: The purpose of this study was to evaluate the utility of gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) for the quantitative evaluation of hepatocellular carcinoma (HCC) and dysplastic nodules in the hepatobiliary phase.
Material and Methods: The subjects comprised 12 patients with 27 lesions (22 HCCs and 5 dysplastic nodules). Chemical-shift-selective fat-suppressed T₁-weighted sequences were obtained before and 10, 20, and 40 min after the injection of Gd-EOB-DTPA. Quantitative analyses were performed with the enhancement ratio of the lesion and the contrast-to-noise (C/N) ratio.
Results: The enhancement ratios of the HCCs were 44.0±36.5, 44.7±46.8, and 47.7±52.8 (%) at 10, 20, and 40 min, respectively, after the injection of Gd-EOB-DTPA. The enhancement ratios of the dysplastic nodules were 36.2±34.3, 44.3±37.3, and 40.1±46.8 (%). The C/N ratios of the HCCs were 0.2±6.6 for the precontrast image, and -9.2±12.6, -9.9±14.8, and -12.7±15.7 at 10, 20, and 40 min, respectively, after the injection of Gd-EOB-DTPA. The C/N ratios of the dysplastic nodules were 1.4±8.0, -13.7±11.1, -13.3±7.6, and -13.1±10.4. No significant differences were found between the HCCs and the dysplastic nodules in the enhancement ratio and the C/N ratio. Only two HCCs showed a positive C/N ratio value, and these HCCs were pathologically confirmed to be a well differentiated and a moderately differentiated carcinoma, respectively.
Conclusion: HCCs and some of the dysplastic nodules showed hypointensity in the hepatobiliary phase in Gd-EOB-DTPA-enhanced MRI. No specific enhancement was observed, regardless of tumor differentiation.

View full abstract

Purpose: To compare the effectiveness of whole body MRI (WB-MRI [magnetic resonance imaging]) and bone scintigram (BS) at detecting bone metastasis.
Materials and Methods: WB-MRI was performed on 16 patients for detecting bone metastasis (6 breast carcinoma, 7 prostatic carcinoma, 1 renal cell carcinoma [RCC], 1 hepatocellular carcinoma [HCC], and 1 primary unknown). BS was also performed in all cases. Patients were placed on a table top extender (Philips Medical Systems). The maximal longitudinal field of view (FOV) was 200 cm. At first, the total spine was imaged in the sagittal plane with a three-station approach for two image sets (fast spin-echo [SE] T₁-weighted images [T₁WI] and short tau inversion recovery [STIR] images). The whole body was then imaged in the coronal plane with a seven-station approach for two image sets (fast field echo [FFE] T₁WI and STIR). Total examination time, including patient positioning, was within 40 min. Three independent radiologists interpreted the imaging data.
Results: WB-MRI identified 5 cases of 24 lesions as bone metastasis, while BS identified 3 cases of 25 lesions. Concordance between WB-MRI and BS was seen in 3 cases of 22 lesions (81%). For two cases of 2 lesions, which were identified only with WB-MRI, the lesions were located in the sacrum and thoracic spine. For one case of 3 lesions, which was identified only with BS, the lesions were located in the skull and rib.
Conclusion: WB-MRI was an excellent method for screening bone metastasis, especially the vertebral body.

View full abstract

Purpose: The decay time of hyperpolarized ¹²⁹Xe in brain tissue depends on the cerebral blood flow (CBF) as well as the longitudinal relaxation time in the tissue (T_1,tissue). Therefore, the decay time is an important parameter for investigating the potential of Xe for cerebral studies. Previous attempts to measure the decay time have been performed after correction of the MR signal for the cosθ decay induced by multiple radiofrequency (RF) excitation pulses. However, since this method requires accurate knowledge of the RF pulse flip angle, the use of a surface coil is restricted because of its nonuniform RF power, distribution. We present a two-pulse protocol for estimating the decay time without the need for flip-angle estimation and demonstrate it in the rat brain.
Method: After rat inhalation of hyperpolarized Xe, two MR spectra of the rat head were obtained at various delay times (4-16 s) and the logarithmic ratio of the two amplitudes was calculated. The decay time was obtained from the slope of the logarithmic ratio against the delay time. The MR measurements were performed with a 4.7T imaging spectrometer with a surface coil located over the head of the anesthetized rat. The gas (25 cc) was smoothly introduced to the lung for 40 s before each measurement began.
Result: From 18 experiments on 11 rats, the decay time was estimated to be 17.7±1.9 s.
Discussion: Assuming a normal rat CBF value, T_1,tissue can be estimated from the decay time to be 26±4 s.

View full abstract

Purpose: Deconvolution based on truncated singular value decomposition (SVD deconvolution) is a promising method for measuring cerebral blood flow (CBF) with dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI), but it has proved extremely sensitive to tracer delay. The purpose of this study was to investigate the effect of regional tracer delay on CBF determined by SVD deconvolution (SVD-CBF). SVD-CBFs with and without correction for the delay were compared with CBF measured by positron emission tomography (PET-CBF), which is regarded as the gold standard for quantification of CBF.
Methods: Perfusion MRI and PET were performed on seven healthy men. In the PET study, the CBF image was obtained with bolus injection of H₂¹⁵O and continuous arterial sampling. In the DSC-MRI study with bolus injection of Gd-based contrast agent, dynamic perfusion data were obtained with a 1.5T scanner at 1-s intervals by means of gradient-echo echo-planar imaging. CBF was determined by the SVD deconvolution method with and without correction for the tracer delay. Region-of-interest measurements were obtained in the gray matter (cerebral cortex in the middle cerebral artery territory) and white matter (centrum semiovale).
Results: Tracer delay was significantly longer in white matter than in gray matter (1.45±0.61 s vs. 0.59±0.35 s, P<0.01). Correction for the delay increased SVD-CBF in the white matter and consequently reduced the gray-to-white SVD-CBF ratio. The uncorrected gray-to-white SVD-CBF ratio was significantly larger than that of PET-CBF (3.33±0.66 vs. 2.54±0.49, P<0.01). However, the gray-to-white delay-corrected SVD-CBF ratio did not differ significantly from that of PET-CBF (2.83±0.31 vs. 2.54±0.49, P=0.10).
Conclusion: The tracer delay in DSC-MRI causes errors in CBF estimates, even in healthy persons, and therefore should be corrected for when delay-sensitive deconvolution, such as SVD deconvolution, is used.

View full abstract

Purpose: The purpose of this study was to investigate the utility of diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) value in differentiating benign and malignant breast lesions and evaluating the detection accuracy of the cancer extension.
Materials and Methods: We used DWI to obtain images of 191 benign and malignant lesions (24 benign, 167 malignant) before surgical excision. The ADC values of the benign and malignant lesions were compared, as were the values of noninvasive ductal carcinoma (NIDC) and invasive ductal carcinoma (IDC). We also evaluated the ADC map, which represents the distribution of ADC values, and compared it with the cancer extension.
Results: The mean ADC value of each type of lesion was as follows: malignant lesions, 1.22±0.31×10^-3 mm²/s; benign lesions, 1.67±0.54×10^-3 mm²/s; normal tissues, 2.09±0.27×10^-3 mm²/s. The mean ADC value of the malignant lesions was statistically lower than that of the benign lesions and normal breast tissues. The ADC value of IDC was statistically lower than that of NIDC. The sensitivity of the ADC value for malignant lesions with a threshold of less than 1.6×10^-3 mm²/s was 95% and the specificity was 46%. A full 75% of all malignant cases exhibited a near precise distribution of low ADC values on ADC maps to describe malignant lesions. The main causes of false negative and underestimation of cancer spread were susceptibility artifact because of bleeding and tumor structure. Major histologic types of false-positive lesions were intraductal papilloma and fibrocystic diseases. Fibrocystic diseases also resulted in overestimation of cancer extension.
Conclusions: DWI has the potential in clinical appreciation to detect malignant breast tumors and support the evaluation of tumor extension. However, the benign proliferative change remains to be studied as it mimics the malignant phenomenon on the ADC map.

View full abstract

We developed a new method employing a balanced turbo field-echo (b-TFE) sequence with progressive spin saturation (PSS) for magnetic resonance angiography (MRA) of the renal arteries during breath-holding without the use of contrast agents. We compared our new method with conventional dynamic MRA of renal arteries. For all portions, renal MRA using b-TFE with PSS was clearer to define (p<0.002) than did conventional dynamic MRA. We confirmed that angiography of renal arteries using b-TFE with PSS was more useful than conventional dynamic MRA.

View full abstract

Array coils play an important role in improving the signal-to-noise ratio (SNR) and achieving parallel imaging; however, one disadvantage of array coils is the nonuniformity of their sensitivity. We propose a simple algorithm to enhance blood vessel visualization in 3D-TOF-MRA (three-dimensional time-of-flight magnetic resonance angiography) utilizing this surface array sensitivity, and we apply it to the MRA data of normal volunteers. We have verified that visualization of peripheral vessels has been remarkably improved.

View full abstract