Molecular imaging using magnetic resonance (MR) imaging has been actively investigated and made rapid progress in the past decade. Applied to cancer gene therapy, the technique's high spatial resolution allows evaluation of gene delivery into target tissues. Because noninvasive monitoring of the duration, location, and magnitude of transgene expression in tumor tissues or cells provides useful information for assessing therapeutic efficacy and optimizing protocols, molecular imaging is expected to become a critical step in the success of cancer gene therapy in the near future. We present a brief overview of the current status of molecular MR imaging, especially in vivo reporter gene imaging using ferritin and other reporters, discuss its application to cancer gene therapy, and present our research of MR imaging detection of electroporation-mediated cancer gene therapy using the ferritin reporter gene.
Purpose: We assessed the value of adding a breath-hold, black-blood, fluid-attenuated, inversion recovery (BH-BB-FLAIR) sequence with a small motion-probing gradient (b=10 s/mm2) using superparamagnetic iron oxide (SPIO) to our present studies that utilize SPIO to detect hepatocellular carcinoma (HCC). We used inversion recovery (IR) in a FLAIR sequence to suppress signals from cysts and a low b-value to suppress vessel signals and provide higher signal to noise than that using high b-value diffusion-weighted imaging. Use of SPIO is expected to reduce the signal in both normal liver parenchyma and in most benign lesions. Materials and Methods: In 19 patients, we reviewed 38 HCC nodules diagnosed by CT arterioportography (CTAP) and CT during hepatic arteriography (CTHA). We divided SPIO-mediated images into sets, those obtained with and without BH-BB-FLAIR. Six radiologists individually interpreted the 2 image sets and sorted them by their confidence levels for the presence of HCC, and we calculated the area under the receiver operating characteristic (ROC) curve (Az) for each image set. Results: On images obtained with BH-BB-FLAIR after SPIO administration, 33 of the 38 HCC nodules appeared as areas of high signal and cyst signal was extinguished. The ROC analysis showed significantly higher Az values in the set with BH-BB-FLAIR (0.89) than in the set without (0.83). Conclusions: Adding BH-BB-FLAIR to existing SPIO-mediated imaging protocols improved detection of HCC nodules and added only 24 s to the scan time.
Purpose: Study of the kidney by apparent diffusion coefficient (ADC) measurements is interesting because of the organ's high blood flow and water transport functions. We investigated the relationship between ADC values of the kidney and the estimated glomerular filtration rate (eGFR). Methods: We retrospectively evaluated 180 patients (113 men, 67 women, aged 20 to 89 years, mean age, 61.06 years) who underwent abdominal magnetic resonance (MR) imaging at 1.5 tesla. Transverse multisection echo-planar diffusion-weighted imaging (DWI) was performed using diffusion gradient b-values of 50 and 1000 s/mm2. Regions of interests (ROIs) were manually delineated in the parenchyma as large as possible at the level of the middle portion of the bilateral kidneys. For each kidney, 2 nonoverlapping ROIs were placed at different locations; 4 total ROIs from the bilateral kidneys were averaged for each patient. ADC values were measured directly from the ROIs. The eGFR was calculated by an equation based on serum creatinine level. The patients were divided into 3 groups: eGFR<30 mL/min/1.73 m2; 30≦eGFR<60; and 60≦eGFR. Results: The mean ADC values of the 3 groups were 1.71±0.18 for the group with eGFR<30 mL/min/1.73 m2; 1.87±0.11 for those with eGFR≥30; and 1.88±0.12×10−3 mm2/s for those with eGFR≥60. The mean ADC values were significantly lower in the patients with eGFR<30 than in the other groups (P<0.05); no difference was found between the other groups; and there was no statistically significant correlation between mean ADC and eGFR values. Conclusion: Patients with low eGFR tended to have lower ADC values. However, this study failed to show significant correlation between mean ADC values and eGFR.
Purpose: Three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) imaging after intratympanic gadolinium injection is useful for pathophysiologic and morphologic analysis of the inner ear. However, statistical analysis of differences in inner ear signal intensity among 3D-FLAIR and other sequences has not been reported. We evaluated the signal intensity of cochlear fluid on each of 3D-FLAIR, 3D-T1-weighted imaging (T1WI), and 3D-constructive interference in the steady state (CISS) to clarify the differences in contrast effect among these 3 sequences using intratympanic gadolinium injection. Methods: Twenty-one patients underwent 3D-FLAIR, 3D-T1WI, and 3D-CISS imaging at 3 tesla 24 hours after intratympanic injection of gadolinium. We determined regions of interest of the cochleae (C) and medulla oblongata (M) on each image, evaluated the signal intensity ratio between C and M (CM ratio), and determined the ratio of cochlear signal intensity of the injected side to that of the non-injected side (contrast value). Results: The CM ratio of the injected side (3.00±1.31, range, 0.53 to 4.88, on 3D-FLAIR; 0.83±0.30, range, 0.36 to 1.58 on 3D-T1WI) was significantly higher than that of the non-injected side (0.52±0.14, range, 0.30 to 0.76 on 3D-FLAIR; 0.49±0.11, range, 0.30 to 0.71 on 3D-T1WI) on 3D-FLAIR and 3D-T1WI (P<0.001), although no significant difference was observed on 3D-CISS (10.03±2.19, range, 5.19 to 14.98, on the injected side; 9.52±1.63 range, 7.48 to 13.48, on the non-injected side) (P=0.11). The mean contrast value on 3D-FLAIR (5.93±2.57, range, 1.22 to 11.05) was significantly higher than that on 3D-T1WI (1.73±0.60, range, 0.98 to 3.09) (P<0.001). Conclusion: The 3D-FLAIR sequence is the most sensitive for observing alteration in inner ear fluid signal after intratympanic gadolinium injection. Our results warrant use of 3D-FLAIR as a sensitive imaging technique to clarify the pathological and morphological mechanisms of disorders of the inner ear.
Purpose: To increase the sensitivity of 3-dimensional fluid-attenuated inversion recovery (3D-FLAIR) to low concentration gadolinium (Gd)-based contrast medium, we optimized sequence parameters on a phantom and evaluated the optimized sequence in patients suspicious for endolymphatic hydrops. Materials and Methods: All scans were performed on a 3-tesla magnetic resonance (MR) unit using a 32-channel head coil. We optimized sequence parameters using a phantom filled with diluted Gd and compared the optimized protocol with 3D-FLAIR using conventional turbo spin echo sequence (3D-FLAIR-CONV). Nine patients underwent scanning using the newly optimized sequence and 3D-FLAIR-CONV 4 hours after double-dose administration of intravenous Gd. We subjectively scored separation of endo- and perilymph space and measured contrast-to-noise ratio (CNR) between endo- and perilymph. Results: The optimized sequence in the phantom study consisted of: repetition time, 9000 ms; echo time, 540 ms; inversion time, 2400 ms; low constant readout flip angle, 120° in the later part of the echo train. Image contrast became heavily T2-weighted (hT2W-3D-FLAIR). In patients, we recognized endolymphatic space for both the cochlea and vesti- bule significantly better by hT2W-3D-FLAIR than 3D-FLAIR-CONV (P<0.01). The mean CNR of the new method was also better than that of 3D-FLAIR-CONV (P<0.01). Conclusions: The newly optimized hT2W-3D-FLAIR was more sensitive than the previous method to low concentration of Gd. Visualization of the endolymphatic space by double-dose administration of intravenous Gd would be more reliable using hT2W-3D-FLAIR.
Chronic expanding hematoma is rare and occasionally misdiagnosed as malignant neoplasm. We describe a case in the female pelvis and correlate findings from pathology and magnetic resonance imaging. On diffusion-weighted images (DWI), our patient's hematoma showed 2 different signal intensities, which corresponded to pathological features of fresh and altered blood components. DWI can distinguish between such pathological features of a chronic expanding hematoma.
We present an alternative method for evaluating cardiac fat tissue-dual gradient-echo in-phase and opposed-phase magnetic resonance imaging (IPOP-MRI) with electrocardiographic (ECG) gating. Conventional IPOP-MRI can be used to evaluate small amounts of fat and is widely used for abdominal imaging, but cardiac motion artifacts make its use difficult for cardiac imaging. Using ECG gating prior to IPOP-MRI, we evaluated lipomatous metaplasia after myocardial infarction. The areas of lipomatous metaplasia measured by IPOP-MRI with ECG gating correlated well with those areas on black-blood T1-weighted imaging (r=0.82, P<0.0001, mean bias−0.29 cm2, limit of agreement±2.06 cm2).
We present magnetic resonance (MR) imaging findings of the brain of a 6-year-old girl with fatal hemophagocytic syndrome (HPS); diffusion-weighted imaging shows abnormal intensity in the white matter and entire corpus callosum. HPS is a rare disorder that affects the mononuclear phagocyte system and not uncommonly involves the central nervous system. Various MR imaging findings of HPS have been reported, but restricted water diffusion throughout the entire corpus callosum lesion and lesions of the white matter have not been reported.