Magnetic resonance imaging evaluation of spontaneous portosystemic collaterals

Three patients, two of whom had histories of episodic hepatic encephalopathy, were shown by magnetic resonance imaging (MRI) to have occult spontaneous portosystemic shunts. The multiplanar imaging capabilities of MRI provided an optimal, noninvasive method of visualization of collateral anatomy in each case.     

Evaluation of portosystemic collaterals by SPECT imaging after endoscopic variceal sclerotherapy: usefulness for predicting recurrence.

Bleeding from esophageal varices is a major cause of morbidity and mortality in cirrhotic patients. Identification of patients at high risk for bleeding is particularly important. The aim of this study was to determine whether detection of portosystemic collaterals by SPECT could predict the outcome of endoscopic injection sclerotherapy of esophageal varices and be useful for selecting appropriate therapy. METHODS: Sixty-two patients with liver cirrhosis who were considered at high risk of bleeding were treated with endoscopic injection sclerotherapy. Endoscopy was performed every 3 mo after therapy or until bleeding occurred. Before and within 2 wk after therapy, tomographic images of intra-abdominal blood pool were constructed by SPECT. RESULTS: Before therapy, the following portosystemic collateral routes were observed: coronary veins in 53 (85.5%) of 62 patients, short gastric veins in 8 patients (12.9%), splenorenal shunts in 10 patients (16.1%), and paraumbilical veins in 6 patients (9.7%). Patients positive for imaging of coronary veins were divided into 3 groups on the basis of changes in images after therapy: complete responders (n = 17), whose coronary vein images disappeared completely; partial responders (n = 18), whose images became smaller; and nonresponders (n = 18), whose images did not change significantly before or after therapy. The rates of recurrence after endoscopic injection sclerotherapy until 6 mo in complete responders (4/17, 23.5%) and partial responders (7/18, 38.9%) were significantly less (P < 0.05) than that in nonresponders (11/13, 84.6%). The rate of recurrence of esophageal varices until 6 mo in nonresponders treated with additional submucosal injection sclerotherapy (1/5, 20.0%) was significantly less (P < 0.05) than that in nonresponders without additional submucosal injection sclerotherapy (11/13, 84.6%). CONCLUSION: Abdominal blood-pool SPECT, a noninvasive method, is useful for evaluating the therapeutic effectiveness of endoscopic sclerotherapy, for predicting the recurrence of varices, and for selecting appropriate management after sclerotherapy.     

Evaluation of portosystemic shunt caused by patent ductus venosus through sequential whole-body scanning using per-sigmoid colon 123I-IMP scintigraphy

Objective The correct estimation of the portosystemic shunt (PSS) ratio prior to surgery for patent ductus venosus is important. Until now, formulas using the lung and liver uptake for per-rectal portal scintigraphy using ¹²³I-iodoamphetamine (IMP) have been mainly used for calculating the PSS ratio. However, these methods did not take radioactivity in the brain or changes in organ radioactivity over time into consideration. Here, we performed sequential whole-body scanning by per-sigmoid colon ¹²³I-IMP scintigraphy, and evaluated the changes in radioactivity in the liver, lungs, and brain over time. Methods The patient was 7-year-old boy with a patent ductus venosus. A 10 Fr. catheter was inserted into the sigmoid colon under fluoroscopic guidance, through which about 55.5 MBq of ¹²³I-IMP was administered. Following the administration, the patient was placed in the supine position and sequential whole-body scanning (from head to thigh) was performed for up to about 80 min. Four regions of interest (ROIs) were placed on the whole brain, lungs, liver, and mediastinum. The PSS ratios were calculated using both the traditional formula (PSS index: brain uptake is not considered) and our original formula (new index: brain uptake is considered). Results Prior to surgery, the radioactivity could be seen clearly in the brain and lungs just following the injection. The liver uptake was faint on the first and second scans (15 min/scan), and increased gradually over time. In contrast, almost no radioactivity was detected in the brain or lungs following surgery. The liver uptake could be seen clearly just following the injection. The new index was significantly higher than the PSS index. Both the new index and the PSS index showed changes over time especially prior to surgery. Conclusions Distinct brain radioactivity was observed early following administration in a patient with PSS. The calculation of the PSS fraction should be performed taking the brain radioactivity into consideration. The timing of the scan should be fixed, but 30 min following administration may be too early to begin scanning.     

Diagnostic performance of using effervescent powder for detection and grading of esophageal varices by multi-detector computed tomography

Purpose

To investigate the effect of using effervescent powder (EP) on the efficacy of multi-detector computed tomography (MDCT) in detection and grading of esophageal varices in cirrhotic patients by considering endoscopy as the gold standard.

Materials and methods

Ninety-two cirrhotic patients undergoing biphasic liver MDCT followed by upper gastrointestinal endoscopy within 4 weeks of MDCT were prospectively evaluated. The patients were divided into two groups before MDCT. The first group (n = 50) received effervescent powder (EP) before and during MDCT procedure and the second group did not receive (n = 42). The presence, size and grade of the esophageal varices were evaluated. MDCT findings were compared with endoscopic results. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of MDCT with EP and without EP were calculated and compared. Correlations between the grades of the varices for each group based on MDCT imaging and endoscopic grading were also evaluated.

Results

The sensitivity, specificity, accuracy, PPV, and NPV of MDCT were 100%, 88%, 96%, 94%, and 100%, respectively, in the EP group, whereas they were 76%, 67%, 74%, 89%, and 43%, respectively, in the non-EP group. Correlations between the grades of the esophageal varices on MDCT and endoscopy were significant in both groups (r = 0.94, p < 0.001 for EP group and r = 0.70, p < 0.001 for non-EP group).

Conclusion

During periodic CT scanning of cirrhotic patients, use of EP increases the success rate of MDCT for detection and grading of esophageal varices.     

Evaluation of the keyhole technique applied to the proton resonance frequency method for magnetic resonance temperature imaging

Purpose:

To evaluate the temporal and spatial resolution of magnetic resonance (MR) temperature imaging when using the proton resonance frequency (PRF) method combined with the keyhole technique.

Materials and Methods:

Tissue‐mimicking phantom and swine muscle tissue were microwave‐heated by a coaxial slot antenna. For the sake of MR hardware safety, MR images were sequentially acquired after heating the subjects using a spoiled gradient (SPGR) pulse sequence. Reference raw (k‐space) data were collected before heating the subjects. Keyhole temperature images were reconstructed from full k‐space data synthesized by combining the peripheral phase‐encoding part of the reference raw data and the center phase‐encoding keyhole part of the time sequential raw data. Each keyhole image was analyzed with thermal error, and the signal‐to‐noise ratio (SNR) was compared with the self‐reference (nonkeyhole) images according to the number of keyhole phase‐encoding (keyhole‐data size) portions.

Results:

In applied keyhole temperature images, smaller keyhole‐data sizes led to more temperature error increases, but the SNR did not decreased comparably. Additionally, keyhole images with a keyhole‐data size of <16 had significantly different temperatures compared with fully phase‐encoded self‐reference images (P < 0.05).

Conclusion:

The keyhole technique combined with the PRF method improves temporal resolution and SNR in the measurement of the temperature in the deeper parts of body in real time. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Assessment of ablative margin by unenhanced magnetic resonance imaging after radiofrequency ablation for hepatocellular carcinoma

Purpose

The aim of this study was to evaluate the feasibility of magnetic resonance imaging (MRI) without a contrast agent to visualize the ablative margin after radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC), compared with enhanced CT.

Methods

Twenty-five HCCs in 19 patients were treated by RFA. T1-weighted MRI was performed before and after RFA, and the signal intensities of the tumors and surrounding liver tissues were measured. Treatment efficacy was assessed based on three grades: margin (+), a continuous high-intensity rim around the index tumor; margin zero, a partially discontinuous high-intensity rim; margin (−), the tumor extends beyond the high-intensity rim.

Results

Twelve (86%) of fourteen low-intensity tumors on the pre-MRI were visualized as low-intensity tumors on post-MRI, and the ablative margins were visualized as high-intensity rims. Two (67%) of three high-intensity tumors on pre-MRI were visualized as higher-intensity tumors in the high-intensity ablative margin. Because the signal intensities of tumors and surrounding tissues in 14 tumors that were low- or high-intensity tumors on pre-MRI increased to the same extent, the tumors and ablative margin could be distinguished on post images. In 6 (75%) of the 8 iso-intensity tumors on pre-MRI, the ablative margin and tumor could also not be discriminated on post-MRI. The overall agreement between MRI and CT for the ablative margin was good (κ coefficient = 0.716, p = 0.00002).

Conclusion

In 82% of low- or high-intensity tumors on pre-MRI, post-MRI without a contrast agent enabled visualization of the ablative margin as a high-intensity rim, and it was possible to evaluate the ablative margin earlier and easier than with enhanced CT.     

Multimodal fusion imaging ensemble for targeted sentinel lymph node management: initial results of an innovative promising approach for anatomically difficult lymphatic drainage in different tumour entities

Purpose There are situations where exact identification and localisation of sentinel lymph nodes (SLNs) are very difficult using lymphoscintigraphy, a hand-held gamma probe and vital dye, either a priori or a posteriori. We developed a new method using a simultaneous injection of two lymphotropic agents for exact topographical tomographic localisation and biopsy of draining SLNs. The purpose of this prospective pilot study was to investigate the feasibility and efficacy of this method ensemble. Methods Fourteen patients with different tumour entities were enrolled. A mixture of ^99mTc-nanocolloid and a dissolved superparamagnetic iron oxide was injected interstitially. Dynamic, sequential static lymphoscintigraphy and SPECT served as pathfinders. MR imaging was performed 2 h after injection. SPECT, contrast MRI and, if necessary, CT scan data sets were fused and evaluated with special regard to the topographical location of SLNs. The day after injection, nine patients underwent SLN biopsy and, in the presence of SLN metastasis, an elective lymph node dissection. Results Twenty-five SLNs were localised in the 14 patients examined. A 100% fusion correlation was achieved in all patients. The anatomical sites of SLNs detected during surgery showed 100% agreement with those localised on the multimodal fusion images. SLNs could be excised in 11/14 patients, six of whom had nodal metastasis. Conclusion Our novel approach of multimodal fusion imaging for targeted SLN management in primary tumours with lymphatic drainage to anatomically difficult regions enables SLN biopsy even in patients with lymphatic drainage to obscure regions. Currently, we are testing its validity in larger patient groups and other tumour entities.     

Evaluation of four postprocessing methods for determination of cerebral blood volume and mean transit time by dynamic susceptibility contrast imaging.

Four different postprocessing methods to determine cerebral blood volume (CBV) and contrast agent mean transit time (MTT) by dynamic susceptibility contrast (DSC) MRI were compared. CBV was determined by two different methods that integrate tracer concentration-time curves numerically and by two other methods that take recirculation into account. For the two methods that use numerical integration, one method cuts the integration after the first pass while the other method integrates over the whole time series. For the two methods that account for recirculation, one method uses a gamma-variate fit, whereas the other method utilizes tissue impulse response. All four methods determine MTT as the ratio of CBV and cerebral blood flow (CBF). In each case, CBF was obtained as the height of the impulse response obtained by deconvolving the tissue concentration-time curves with a noninvasively determined arterial input function. Monte Carlo simulations were performed to determine the reliability of the methods and the validity of the simulations was supported by observation of similar trends in 13 acute stroke patients. The method of determining CBV and subsequently MTT was found to affect the measured value especially in areas where MTT is prolonged, but had no apparent effect on the visually determined hypoperfusion volumes.     

Evaluation of [11C]SA5845 and [11C]SA4503 for imaging of sigma receptors in tumors by animal PET

Sigma receptors are expressed in a wide variety of tumor cell lines, and are expressed in proliferating cells. A radioligand for the visualization of sigma receptors could be useful for selective detection of primary tumors and their metastases, and for non-invasive assessment of tumor proliferative status. To this end we evaluated two sigma receptor ligands, [11C]SA5845 and [11C]SA4503. In an in vitro study, AH109A hepatoma showed moderate densities of sigma1 and sigma2 receptors, and VX-2 carcinoma showed a high density of sigma2 receptors: Bmax (fmol/mg protein) for sigma1 vs. sigma2, 1,700 vs. 1,200 for AH109A hepatoma and 800 vs. 10,000 for VX-2 carcinoma. In a cell growth assay in vitro, neither SA5845 nor SA4503 (<10 microM) showed any inhibitory effect on proliferation of the AH109A hepatoma cells. In rats, the uptake of [11C]SA5845 and [11C]SA4503 in AH109A tissues was accumulated over the first 60 minutes; however, the uptake of both tracers increased by co-injection with haloperidol as a sigma receptor ligand. On the other hand, in the PET studies of rabbits, the uptake of [11C]SA5845 in the VX-2 carcinoma was relatively higher than that of [11C]SA4503, because of a much higher density of sigma2 receptors compared to sigma1 receptors in the VX-2 tissue, and the uptake of both tracers in the VX-2 tissue was decreased by carrier-loading and pre-treatment with haloperidol ([11C]SA5845, 53% and 26%, respectively; [11C]SA4503, 41% and 22%, respectively at 30 minutes after injection). Therefore, [11C]SA5845 and [11C]SA4503 may be potential ligands for PET imaging of sigma receptor-rich tumors.