Breath-hold spin-echo MR imaging for evaluation of dynamic enhancement of native and treated hepatocellular carcinoma after intravenous Gd-DTPA administration

Using a simple modification of a standard spin-echo sequence which enables acquisition of three breath-hold images in 15 s, dynamic enhancement of 30 histologically proven hepatocellular carcinomas (17 native tumors, 6 completely necrotic tumors after nonsurgical treatments, and 7 tumors with viable and necrotic portions) after intravenous injection of gadolinium-DTPA was evaluated. Native hepatocellular carcinomas and viable portions in treated nodules showed elective enhancement in images obtained 40 s after contrast injection. Contrast between these lesions and the normal liver decreased thereafter. No contrast uptake was seen in entirely necrotic nodules and necrotic portions of treated nodules. Because of the capability to demonstrate the elective arterial blood supply typical of hepatocellular carcinoma, breath-holdT ₁-weighted spin-echo sequence should replace conventionalT ₁-weighted images for the evaluation of intravenously administered gadolinium-DTPA enhancement of this tumor before and after nonsurgical treatments.     

T2-weighted breathold imaging of the liver: a quantitative and qualitative comparison of fast spin echo and half Fourier single shot fast spin echo imaging

The imaging characteristics of two EPI-hybrid breath-hold sequences, T2-weighted fast spin-echo [FSE, effective echo time (TE_eff) 138ms] and half Fourier single shot turbo spin-echo (HASTE, TE_eff 60 ms), were compared in hepatic imaging. A total of 111 patients with suspected hepatic disease were studied at 1.5 Tesla using a body phase-array coil. The signal-to-noise (S/N) and contrast-to-noise (C/N) ratios for organs and lesions were calculated and quantitatively compared. Organ delineation, visualization of anatomical structures and pathological lesions, artifacts, and total image quality were qualitatively assessed and statistically compared. The final diagnoses were metastases from colorectal, breast, and pancreatic cancer in 23/111, hepatocellular carcinoma in 15/111, cysts in 19/111, hemangiomas in 9/111, several other lesions in 7/111, and no lesions in 38/111 of the cases. A total of 139 lesion in 73% of the patients were seen while 85% of the lesions were at least 1.5 cm in size. Regarding S/Ns HASTE was significantly (P<0.03) superior to FSE with only minor (P>0.05) differences in C/Ns between the two sequences for anatomical and pathological structures. HASTE demonstrated in almost all (97.3%) of the cases no artifacts, while on fast SE imaging moderate to minor artifacts were present in 23.5–51.7% of the cases. The overall image quality and diagnostic confidence was rated significantly higher (good 43.2%, excellent 53.2%) for HASTE than for fast SE imaging (good 44.8%, excellent 17.6%). Providing comparable C/Ns for anatomical and pathological structures, breatheld HASTE imaging proved to be superior to fast SE in T2-weighted imaging of the upper abdomen regarding general image quality, and, with adequate technical prerequisites, may be a suitable substitute of fast T2-imaging techniques.     

Breathhold imaging of the upper abdomen using a circular polarized-array coil: comparison with standard body coil imaging

Current studies emphasize the use of array coils to decrease noise and increase the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). We applied Tl-weighted and T2-weighted standard nonbreathhold spin echo (SE) sequences and Tl-weighted FLASH, TurboFLASH, T2-weighted spin-echo time (TSE), and heavily T2-weighted half Fourier acquisition single-shot TSE (HASTE) sequences during breathhold for abdominal imaging in 15 normal volunteers. The breathhold scans were performed using both a standard coil and a circular polarized array coil. We analyzed the signal intensity (SI), SNR, and CNR of abdominal organs in all sequences. SNRs increased in all cases by an overall factor of 3 due to an 8% increase in overall Sis and a 50% decrease in noise when applying the array coil. Although the array-coil FLASH sequence performed at least as well as the respective SE sequence, the SNRs of the array-coil TurboFLASH, TSE breathhold, and HASTE sequences were generally lower. We conclude that array-coil imaging significantly improves fast imaging of the abdomen.     

Magnetic resonance evaluation of autonomous thyroid nodules treated by percutaneous ethanol injection

Magnetic resonance (MR) imaging was used to evaluate the effect of ultrasound-guided percutaneous ethanol injection (PEI) of autonomous thyroid nodules (ATNs). Nine patients affected with ATN (3.7–32.2 mL volume) underwent PEI (4–19 mL ethanol, subdivided in 3–6 weekly procedures). MR imaging (1.5 T) was performed before each alcoholization and 1 month after the last PEI procedure with the following parameters:T ₁-(550/12) andT ₂-weighted (2200/160) spin-echo images; 4-mm slices, 10% gap; coronal planes. A further seven patients with normal thyroid function, who had undergone PEI 6–18 months before, underwent an MR examination with the same parameters. The signal-to-noise ratio (S/N) of ATN and extranodular gland, as well as ATN volume, were evaluated on theT ₂-weighted images. OnT ₁-weighted images, ATNs appeared mostly hypointense before treatment, with hyperintense areas during treatment, and were lightly hyperintense 6–18 months after treatment. S/N onT ₂-weighted images: extranodular gland 3.5–9.2; ATNs, before treatment 13.2–19.7, before the last procedure 7.7–11.6, 1 month after the last procedure 5.6–10.9; previously treated ATNs, 4.3–8.2. No significant volume reduction was observed with MR 1 month after the last procedure. The MR examination time was about 15 minutes. In conclusion, the effect of PEI on ATNs can be evaluated with an MR examination that is not very time consuming.     

Turbo spin-echo sequences in magnetic resonance imaging of the brain: Physics and applications

Fast SE imaging provides considerable measure time reduction, high signal-to-noise ratios as well as similar contrast behavior compared to conventional SE sequences. Besides TR and TE_eff, echo train length (ETL), interecho time , and-space trajectory determine image contrast and image quality in fast SE sequences. True proton density contrast (CSF hypointense) and not too strong T2 contrast are essential requirements in routine brain MRI. A Turbo SE sequence with very short echo train length (ETL=3), short TE_eff and short interecho time (17 ms), and TR=2000 ms was selected for proton density contrast; a Turbo SE sequence with ETL=7, TE_eff=90 ms, =22 ms, and TR=3250 ms was selected for T₂-weighted images. Using both single-echo Turbo SE sequences yielded 50% measure time reduction compared to the conventional SE technique. Conventional SE and optimized Turbo SE sequences were compared in 150 patients resulting in very similar signal and contrast behavior. Furthermore, reduced flow artifacts in proton density—and especially in T₂-weighted Turbo SE images—and better contrast of high-intensity lesions in proton density-weighted Turbo SE images were found. Slightly reduced edge sharpness—mainly in T₂-weighted Turbo SE images—did not reduce diagnostic reliability. Differences between conventional and Turbo SE images concerning image contrast and quality are explained regarding special features of fast SE technique.Address for correspondence: Institut für Röntgendiagnostik, Klinikum der Universität Regensburg, Franz-Josef-Strauß-Allee 11, 93042 Regensburg, Germany. Additional reprints of this chapter may be obtained from the Reprints Department, Chapman & Hall, One Venn Plaza, New York, NY 10119.     

Acoustic noise reduction in <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript>- and proton-density-weighted turbo spin-echo imaging

Objective

To reduce acoustic noise levels in T ₁-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice.

Materials and methods

Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison.

Results

An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1–4) and the acquisition of half the number of slices per TR only. Image quality in terms of SNR and CNR was found to be preserved.

Conclusions

The proposed measures in this study allowed a threefold reduction in the acoustic perception of T ₁-weighted and proton-density-weighted TSE sequences compared to a standard TSE-acquisition. This could be achieved without visible degradation of image quality, showing the potential to improve patient comfort and scan acceptability.

     

A comparison of phase imaging and quantitative susceptibility mapping in the imaging of multiple sclerosis lesions at ultrahigh field

Objective

The aim of this study was to compare the use of high-resolution phase and QSM images acquired at ultra-high field in the investigation of multiple sclerosis (MS) lesions with peripheral rings, and to discuss their usefulness for drawing inferences about underlying tissue composition.

Materials and methods

Thirty-nine Subjects were scanned at 7 T, using 3D T ₂*-weighted and T ₁-weighted sequences. Phase images were then unwrapped and filtered, and quantitative susceptibility maps were generated using a thresholded k-space division method. Lesions were compared visually and using a 1D profiling algorithm.

Results

Lesions displaying peripheral rings in the phase images were identified in 10 of the 39 subjects. Dipolar projections were apparent in the phase images outside of the extent of several of these lesions; however, QSM images showed peripheral rings without such projections. These projections appeared ring-like in a small number of phase images where no ring was observed in QSM. 1D profiles of six well-isolated example lesions showed that QSM contrast corresponds more closely to the magnitude images than phase contrast.

Conclusions

Phase images contain dipolar projections, which confounds their use in the investigation of tissue composition in MS lesions. Quantitative susceptibility maps correct these projections, providing insight into the composition of MS lesions showing peripheral rings.

     

T 2 relaxometry measurements in low spatial frequency brain regions differ between fast spin-echo and multiple-echo spin-echo sequences

Object

Dual-echo fast spin-echo (FSE) sequences are used in T ₂ relaxometry studies of neurological disorders because of shorter clinical scanning times and protocol simplicity. However, FSE sequences have possible spatial frequency-dependent effects, and derived T ₂ values may include errors that depend on the spatial frequency characteristics of the brain region of interest.

Materials and methods

Dual-echo FSE and multi-echo spin-echo (MESE) sequences were acquired in nine subjects. The T ₂ decay curves for FSE and MESE sequences were estimated and percent error maps were generated. T ₂ error values were obtained along each patient’s corticospinal tract (CST). Whole-brain white matter (WM) and gray matter (GM) T ₂ error values were also obtained. The paired t test was performed to evaluate differences in T ₂ values in the CST between FSE and MESE sequences.

Results

Histograms of error values in CST and in whole-brain WM and GM structures revealed systematic errors in FSE sequences. Significant differences (P < 0.001) in CST T ₂ values were also observed between FSE and MESE sequences.

Conclusion

Our findings indicate that T ₂ values derived from FSE sequences are prone to large errors, even in low spatial frequency regions such as the CST, when compared to MESE sequences. Future studies should be aware of this limitation of FSE sequences.     

High-resolution MR imaging appearance of colonic tissue in rabbits using an endoluminal coil

Purpose: This study assessed the value of high-resolution magnetic resonance imaging (MRI) of the distal colon by means of a dedicated endoluminal magnetic resonance receiver coil on a 1.5-T clinical scanner. Materials and Methods: To this end, single-loop, receive-only radio-frequency coils, housed in 18 F sheaths, were built. A 1.5-T clinical imager was used. A 18 French diameter internal MRI receiver coil was inserted into the distal colon in 15 New Zealand rabbits to obtain high-resolution magnetic resonance images by using T1-weighted Flash sequences with and without Fat Saturation (FS), T2-weighted True-Fisp, turbo spin-echo, and T1-weighted Flash FS after contrast media injection. Images were compared to histological sections. Results: An adequate image quality was obtained in all specimens without significant artefacts. Based on histological reports, a five-layer structure of the wall was considered normal. On different MR sequences, only two layers were identified on the images of all rabbits specimens. The nearest layer to the mucosal surface was usually seen as a hyper intense layer and likely corresponds to the mucosa. The highest difference of signal value between internal and external layers was performed on 2D Fat saturation T1 weighted gradient echo. Comparison of mean signal value between the internal and external layers was statistically different in for each sequence used in our protocol (P< 0.05). Conclusion: Dedicated endoluminal RF coil provides good spatial resolution at the region of interest. On this prospective study of in vivo rabbit, evaluation of colon walls allowed to provide detailed information.     

Enhancement characteristics of hepatic focal nodular hyperplasia and its scar by dynamic magnetic resonance imaging

Rationale and objectives: To determine the relationship between the lesion and the scar enhancement characteristics in a series of hepatic Focal Nodular Hyperplasia (FNH) lesions studied with dynamic MR imaging.Methods: Nine patients with FNH were studied. The slice showing the largest scar was selected for the dynamic single slice T1-weighted Gradient-echo sequence before and after contrast administration (15 images, one every 20 s). Analysis was performed with ROI measurements in the lesion and the scar. Signal-intensity and enhancement curves were obtained from both structures.Results: Dynamic MRI showed the typical homogeneous early enhancement of the lesion with delayed enhancement of the scar. The scar enhanced early and vigorously in all cases. Two patterns of enhancement curves were defined. In the parallel pattern, both curves started early, quickly reaching a plateau maintained over time (77.8%). In the divergent pattern the curve of the scar was above the curve of the FNH (22.2%). after the maximum slope was reached, with progressive separation of the curves.Conclusion: There is a hypervascular scar enhancement within FNH lesions with either a parallel or divergent course after the maximum early enhancement.     

Magnetic resonance imaging at 1.5 T with immunospecific contrast agent in vitro and in vivo in a xenotransplant model

Object: Demonstrating the feasibility of magnetic resonance imaging (MRI) at 1.5 T of ultrasmall particle iron oxide (USPIO)-antibody bound to tumor cells in vitro and in a murine xenotransplant model. Methods: Human D430B cells or Raji Burkitt lymphoma cells were incubated in vitro with different amounts of commercially available USPIO-anti-CD20 antibodies and cell pellets were stratified in a test tube. For in vivo studies, D430B cells and Raji lymphoma cells were inoculated subcutaneously in immunodeficient mice. MRI at 1.5 T was performed with T1-weighted three-dimensional fast field echo sequences (17/4.6/13°) and T2-weighted three-dimensional fast-field echo sequences (50/12/7°). For in vivo studies MRI was performed before and 24 h after USPIO-anti-CD20 administration. Results: USPIO-anti-CD20-treated D430B cells, showed a dose-dependent decrease in signal intensity (SI) on T2*-weighted images and SI enhancement on T1-weighted images in vitro. Raji cells showed lower SI changes, in accordance to the fivefold lower expression of CD20 on Raji with respect to D430B cells. In vivo 24 h after USPIO-anti-CD20 administration, both tumors showed an inhomogeneous decrease of SI on T2*-weighted images and SI enhancement on T1-weighted images. Conclusions: MRI at 1.5 T is able to detect USPIO-antibody conjugates targeting a tumor-associated antigen in vitro and in vivo.     

Liver and spleen enhancement after intravenous injection of carboxydextran magnetite: effect of dose,delay of imaging,and field strength in anex vivo model

It has been predicted that liver and spleen enhancement after administration of superparamagnetic contrast agents may be different, depending on the strength of the main magnetic field. With the use of anex vivo model, we investigated at 0.3, 0.5, and 1.5 T the effects on liver and spleen signal intensity of 5, 15, and 45 µmol/kg body weight of dextran magnetite (SHU 555A) in 54 rats. Nine rats served as controls. At different time delays since injection, the animals were killed, and after perfusion with saline, the liver, brain, and spleen were fixed in formalin. The specimens were embedded in an agar gel matrix and imaged with inversion recovery T1-weighted, proton density spin echo, and T2*-weighted gradient recalled echo (GRE) sequences. At each magnetic field strength, peak liver and spleen signal loss increased with increasing dose of the contrast medium. Signal loss was significantly more conspicuous after a dose of 15 than 5 µmol/kg body weight, but not after a dose of 45 compared with 15 µmol/kg. No signal change was observed in the brain. GRE images showed higher enhancement than proton density-weighted spin echo and inversion recovery images but were noisier. The enhancement showed a plateau between 30 min and 24 hours. Only the signal decrease of the liver after a low dose of contrast medium on GRE images was significantly higher (p<0.01) at 1.5 than at 0.5 and 0.3 T. Other differences in respect to the field strength were less significant (p<0.05) or nonsignificant. Differences in the spleen enhancement were nonsignificant. SHU 555A at a dose of 15 µmol/kg is an efficient intracellular contrast agent for liver and spleen at low, mid, and high field strength. Proton density spin echo images are probably the sequence of choice to exploit SHU 555A contrast effects and a wide time window for imaging after its intravenous injection does exist.     

NMR microscopy of single neurons at 500 MHZ

Previous NMR microimaging studies at 360 MHz have demonstrated a clear differentiation between the nucleus and cytoplasm in isolated single neurons. In particular, theT ₂ of the cell nucleus is 2.5 times larger than that of the cytoplasm. In order to determine the magnitude of possibleT ₂ ^* influences on these observations, images of single cells have been obtained at 500 MHz using spin-echo and line-narrowing sequences. Comparison of the images acquired by the two sequences, and of the spin-echo images at 360 and 500 MHz, imply that anyT ₂ ^* contributions are relatively small. Consequently, the measuredT ₂ differences in spin-echo imaging represent a true difference in theT ₂ relaxation in the two cellular compartments.     

Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T

The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T₁- and T₂-weighted MR imaging was performed to follow tumor growth. T₁-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T₂-weighted images.Measurements of T₁ and T₂ relaxation times were performed with inversion recovery FLASH and Carr–Purcell–Meiboom–Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T₁ and T₂ of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T₁ relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment.     

Magnetic resonance imaging differentiation of adrenal masses at 1.5 t: t2-weighted images,chemical shift imaging,and gd-dtpa dynamic studies

The purpose of our study was to assess the potential role of spin-echo (SE), chemical shift, and gadolinium-enhanced magnetic resonance imaging (MRI) in the differentiation of adrenal masses.Seventy-two adrenal masses (26 nonhyperfunctioning adenomas, 16 aldosterone-secreting adenomas and 6 other different benign cortical masses, 18 pheochromocytomas, and 6 malignant masses) in 63 patients were evaluated with spin-echo sequences, chemical shift imaging (CSI) and gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA) dynamic studies. Ratios and indices of signal intensity for all examined MRI methods were calculated and examined for significance of difference between different types of adrenal masses.Quantitative magnetic resonance evaluation of adrenal masses showed significant differences (at least<0.01) between nonhyperfunctioning adenomasvs. pheochromocytomas orvs. malignant lesions orvs. aldosterone-secreting adenomas and between pheochromocytomasvs. malignant lesions. The most specific indicators of adrenal mass character proved to be the CSI ratio based on opposed-phase and in-phase two-dimensional fast low-angle shot (FLASH) images, reflecting lipid content in the lesion, and Gd-DTPA dynamic studies ratios reflecting contrast agent inflow and washout in the lesion: Wo_max/last and Dyn_1.2–3.2. There was no overlap of CSI ratio between adenomas and pheochromocytomas. The overlap of ranges of CSI ratio between nonhyperfunctioning adenomas and aldosterone-secreting adenomas was only 18.5%. There was no overlap of Wo_max/last ratio between adenomas and pheochromocytomas, or adenomas and malignant lesions. The overlap of ranges of Dyn_{1.2– 3.2} ratio between pheochromocytomas and malignant lesions was only 17.6%.MRI enables good visualization and specific characterization of adrenal masses. The optimal MRI protocol for the adrenal region is presented.Address for correspondence: Imaging Department, Warsatv Province Hospital, ul. Kondratowicza 8, 03-285 Warsaw, Poland.     

Low-field magnetic resonance imaging of the pelvis in patients with anal dynamic graciloplasty: initial experience

The aim of this study was to determine whether low-field magnetic resonance (MR) imaging can safely and accurately depict inflammatory changes in patients with anal dynamic graciloplasty, in whom high-field MR imaging is contraindicated and ultrasonography and computed tomography are inadequate. A 0.2-T field-strength MR examination was performed in six patients with anal dynamic graciloplasty malfunction in whom reoperation was contemplated. The following sequences were applied:T ₂-weighted turbo spinecho with fat saturation,T ₁-weighted conventional spin-echo, and contrastenhancedT ₁-weighted conventional spin-echo with fat saturation. Results indicated that none of the patients experienced relevant discomfort, pacemaker malfunction, or electrode dislocation with low-field MR imaging. Inflammatory pelvic changes were visualized in four patients and atrophy of the transposed gracilis muscle in another. Surgery was thus avoided in the four, who underwent conservative treatment for their pelvic inflammation. It was concluded that these prelininary results demonstrate the feasibility of MR imaging with a low field strength in patients with anal dynamic graciloplasty. In such patients, in whom diagnostic imaging had been problematic, the potential for safe and accurate visualization will be a boon to treatment planning.     

3D <Emphasis Type="Italic">T</Emphasis><Subscript>2</Subscript>-weighted imaging at 7T using dynamic k<Subscript>T</Subscript>-points on single-transmit MRI systems

Objectives

For turbo spin echo (TSE) sequences to be useful at ultra-high field, they should ideally employ an RF pulse train compensated for the B ₁ ⁺ inhomogeneity. Previously, it was shown that a single k_T-point pulse designed in the small tip-angle regime can replace all the pulses of the sequence (static k_T-points). This work demonstrates that the B ₁ ⁺ dependence of T ₂-weighted imaging can be further mitigated by designing a specific k_T-point pulse for each pulse of a 3D TSE sequence (dynamic k_T-points) even on single-channel transmit systems

Materials and methods

By combining the spatially resolved extended phase graph formalism (which calculates the echo signals throughout the sequence) with a gradient descent algorithm, dynamic k_T-points were optimized such that the difference between the simulated signal and a target was minimized at each echo. Dynamic k_T-points were inserted into the TSE sequence to acquire in vivo images at 7T.

Results

The improvement provided by the dynamic k_T-points over the static k_T-point design and conventional hard pulses was demonstrated via simulations. Images acquired with dynamic k_T-points showed systematic improvement of signal and contrast at 7T over regular TSE—especially in cerebellar and temporal lobe regions without the need of parallel transmission.

Conclusion

Designing dynamic k_T-points for a 3D TSE sequence allows the acquisition of T ₂-weighted brain images on a single-transmit system at ultra-high field with reduced dropout and only mild residual effects due to the B ₁ ⁺ inhomogeneity.

     

Rat cerebral ischemia induced with photochemical occlusion of proximal middle cerebral artery: a stroke model for MR imaging research

A stroke model in rats with photochemically induced thrombosis (PIT) of proximal cerebral middle artery (MCA) is introduced for magnetic resonance imaging (MRI) study. Thirty-seven rats subjected to surgical and optical procedures for inducing the PIT models were scanned using a 1.5-T scanner with T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI), and contrast-enhanced perfusion-weighted imaging (PWI) at 1 h and 24 h after MCA occlusion. The penumbra evolution and PWI-derived parameters including relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) were monitored; and the relative lesion size (RLS) was compared with the final RLS on the gold standard triphenyl tetrazolium chloride (TTC) staining at 24 h. The results showed that the focal cerebral ischemic lesions were detectable in all rats with different MR approaches. The lesion on PWI at 1 h and on all MR images at 24 h was matched well with that seen on TTC staining; the peri-infarct area decreased from 6.2 ± 7.2% of the brain volume at 1 h to 0.3 ± 5.6% at 24 h. Compared to that in the contralateral hemisphere, rCBV in ischemic region was 52.6 ± 21.4 and 40.0 ± 15.8% (p > 0.05), and rCBF was 64.6 ± 11.2 and 47.3 ± 11.1% (p < 0.05) at 1 h and 24 h respectively. The present PIT model in rats has been successfully adopted for MRI research, which might be feasible for certain stroke studies and should be beneficial for the evaluation on effects of potential diagnostic and therapeutic approaches.     

Cranial fixation plates in cerebral magnetic resonance imaging: a 3 and 7 Tesla in vivo image quality study

Objective

This study assesses and quantifies impairment of postoperative magnetic resonance imaging (MRI) at 7 Tesla (T) after implantation of titanium cranial fixation plates (CFPs) for neurosurgical bone flap fixation.

Materials and methods

The study group comprised five patients who were intra-individually examined with 3 and 7 T MRI preoperatively and postoperatively (within 72 h/3 months) after implantation of CFPs. Acquired sequences included T₁-weighted magnetization-prepared rapid-acquisition gradient-echo (MPRAGE), T₂-weighted turbo-spin-echo (TSE) imaging, and susceptibility-weighted imaging (SWI). Two experienced neurosurgeons and a neuroradiologist rated image quality and the presence of artifacts in consensus reading.

Results

Minor artifacts occurred around the CFPs in MPRAGE and T₂ TSE at both field strengths, with no significant differences between 3 and 7 T. In SWI, artifacts were accentuated in the early postoperative scans at both field strengths due to intracranial air and hemorrhagic remnants. After resorption, the brain tissue directly adjacent to skull bone could still be assessed. Image quality after 3 months was equal to the preoperative examinations at 3 and 7 T.

Conclusion

Image quality after CFP implantation was not significantly impaired in 7 T MRI, and artifacts were comparable to those in 3 T MRI.

     

Comparison of T1-weighted 2D TSE, 3D SPGR,and two-point 3D Dixon MRI for automated segmentation of visceral adipose tissue at 3 Tesla

Objectives

To evaluate and compare conventional T1-weighted 2D turbo spin echo (TSE), T1-weighted 3D volumetric interpolated breath-hold examination (VIBE), and two-point 3D Dixon-VIBE sequences for automatic segmentation of visceral adipose tissue (VAT) volume at 3 Tesla by measuring and compensating for errors arising from intensity nonuniformity (INU) and partial volume effects (PVE).

Materials and methods

The body trunks of 28 volunteers with body mass index values ranging from 18 to 41.2 kg/m² (30.02 ± 6.63 kg/m²) were scanned at 3 Tesla using three imaging techniques. Automatic methods were applied to reduce INU and PVE and to segment VAT. The automatically segmented VAT volumes obtained from all acquisitions were then statistically and objectively evaluated against the manually segmented (reference) VAT volumes.

Results

Comparing the reference volumes with the VAT volumes automatically segmented over the uncorrected images showed that INU led to an average relative volume difference of ?59.22 ± 11.59, 2.21 ± 47.04, and ?43.05 ± 5.01 % for the TSE, VIBE, and Dixon images, respectively, while PVE led to average differences of ?34.85 ± 19.85, ?15.13 ± 11.04, and ?33.79 ± 20.38 %. After signal correction, differences of ?2.72 ± 6.60, 34.02 ± 36.99, and ?2.23 ± 7.58 % were obtained between the reference and the automatically segmented volumes. A paired-sample two-tailed t test revealed no significant difference between the reference and automatically segmented VAT volumes of the corrected TSE (p = 0.614) and Dixon (p = 0.969) images, but showed a significant VAT overestimation using the corrected VIBE images.

Conclusion

Under similar imaging conditions and spatial resolution, automatically segmented VAT volumes obtained from the corrected TSE and Dixon images agreed with each other and with the reference volumes. These results demonstrate the efficacy of the signal correction methods and the similar accuracy of TSE and Dixon imaging for automatic volumetry of VAT at 3 Tesla.