MRI-guided vascular access with an active visualization needle

Purpose:

To develop an approach to vascular access under magnetic resonance imaging (MRI), as a component of comprehensive MRI‐guided cardiovascular catheterization and intervention.

Materials and Methods:

We attempted jugular vein access in healthy pigs as a model of “difficult” vascular access. Procedures were performed under real‐time MRI guidance using reduced field of view imaging. We developed an “active” MRI antenna‐needle having an open‐lumen, distinct tip appearance and indicators of depth and trajectory in order to enhance MRI visibility during the procedure. We compared performance of the active needle against an unmodified commercial passively visualized needle, measured by procedure success among operators with different levels of experience.

Results:

MRI‐guided central vein access was feasible using both the active needle and the unmodified passive needle. The active needle required less time (88 vs. 244 sec, P = 0.022) and fewer needle passes (4.5 vs. 9.1, P = 0.028), irrespective of operator experience.

Conclusion:

MRI‐guided access to central veins is feasible in our animal model. When image guidance is necessary for vascular access, performing this component under MRI will allow wholly MRI‐guided catheterization procedures that do not require adjunctive imaging facilities such as x‐ray or ultrasound. The active needle design showed enhanced visibility, as expected. These capabilities may permit more complex catheter‐based cardiovascular interventional procedures enabled by enhanced image guidance. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Gadoxetic acid‐enhanced MRI versus multiphase multidetector row computed tomography for evaluating the viable tumor of hepatocellular carcinomas treated with image‐guided tumor therapy

Purpose:

To compare the diagnostic performance of gadoxetic acid‐enhanced MRI with that of multi‐phase 40‐ or 64‐multidetector row computed tomography (MDCT) to evaluate viable tumors of hepatocellular carcinomas (HCCs) treated with image‐guided tumor therapy.

Materials and Methods:

A total of 108 patients with 162 HCCs (56 lesions with viable tumor and 106 without viable tumor) treated by means of transcatheter arterial chemoembolization or radiofrequency ablation were retrospectively included in this study. All patients underwent multi‐phase CT at 40‐ or 64‐MDCT and gadoxetic acid‐enhanced MRI using 3.0 Tesla (T). Two observers independently and randomly reviewed the CT and MR images of the treated lesions. The diagnostic performance of two techniques for the evaluation of the viable tumors in the treated lesions was assessed with a receiver operating characteristic (ROC) analysis.

Results:

For each observer, the areas under the ROC curve were 0.953 and 0.969 for MRI, and 0.870 and 0.888 for MDCT (P < 0.05). The diagnostic accuracies (96.3% for each observer) and sensitivities (92.9% and 96.4%) of MRI in two observers were significantly higher than those (82.7% and 80.9%, 53.6% for each observer, respectively) of MDCT (P < 0.001). The negative predictive values (96.3% and 98.1%) of MRI in two observers were significantly higher than those (80.0% and 79.5%) of MDCT (P < 0.001). For each observer, specificities and positive predictive values did not differ significantly between the two techniques (P > 0.05).

Conclusion:

Gadoxetic acid‐enhanced MRI shows better diagnostic performance than that of MDCT for evaluating the viable tumors of HCCs treated with image‐guided tumor therapy. J. Magn. Reson. Imaging 2010;32:629–638. © 2010 Wiley‐Liss, Inc.     

Transperineal prostate biopsy under magnetic resonance image guidance: a needle placement accuracy study

Purpose

To quantify needle placement accuracy of magnetic resonance image (MRI)‐guided core needle biopsy of the prostate.

Materials and Methods

A total of 10 biopsies were performed with 18‐gauge (G) core biopsy needle via a percutaneous transperineal approach. Needle placement error was assessed by comparing the coordinates of preplanned targets with the needle tip measured from the intraprocedural coherent gradient echo images. The source of these errors was subsequently investigated by measuring displacement caused by needle deflection and needle susceptibility artifact shift in controlled phantom studies. Needle placement error due to misalignment of the needle template guide was also evaluated.

Results

The mean and standard deviation (SD) of errors in targeted biopsies was 6.5 ± 3.5 mm. Phantom experiments showed significant placement error due to needle deflection with a needle with an asymmetrically beveled tip (3.2–8.7 mm depending on tissue type) but significantly smaller error with a symmetrical bevel (0.6–1.1 mm). Needle susceptibility artifacts observed a shift of 1.6 ± 0.4 mm from the true needle axis. Misalignment of the needle template guide contributed an error of 1.5 ± 0.3 mm.

Conclusion

Needle placement error was clinically significant in MRI‐guided biopsy for diagnosis of prostate cancer. Needle placement error due to needle deflection was the most significant cause of error, especially for needles with an asymmetrical bevel. J. Magn. Reson. Imaging 2007;26:688–694. © 2007 Wiley‐Liss, Inc.     

MRI‐guided procedures in various regions of the body using a robotic assistance system in a closed‐bore scanner: Preliminary clinical experience and limitations

Purpose:

To present the clinical setup and workflow of a robotic assistance system for image‐guided interventions in a conventional magnetic resonance imaging (MRI) environment and to report our preliminary clinical experience with percutaneous biopsies in various body regions.

Materials and Methods:

The MR‐compatible, servo‐pneumatically driven, robotic device (Innomotion) fits into the 60‐cm bore of a standard MR scanner. The needle placement (n = 25) accuracy was estimated by measuring the 3D deviation between needle tip and prescribed target point in a phantom. Percutaneous biopsies in six patients and different body regions were planned by graphically selecting entry and target points on intraoperatively acquired roadmap MR data.

Results:

For insertion depths between 29 and 95 mm, the average 3D needle deviation was 2.2 ± 0.7 mm (range 0.9–3.8 mm). Patients with a body mass index of up to ≈30 kg/m² fitted into the bore with the device. Clinical work steps and limitations are reported for the various applications. All biopsies were diagnostic and could be completed without any major complications. Median planning and intervention times were 25 (range 20–36) and 44 (36–68) minutes, respectively.

Conclusion:

Preliminary clinical results in a standard MRI environment suggest that the presented robotic device provides accurate guidance for percutaneous procedures in various body regions. Shorter procedure times may be achievable by optimizing technical and workflow aspects. J. Magn. Reson. Imaging 2010;31:964–974. ©2010 Wiley‐Liss, Inc.     

MRI‐guided vacuum‐assisted breast biopsy: A phantom and patient evaluation of targeting accuracy

Purpose

To determine the spatial localization errors of magnetic resonance imaging (MRI)‐guided core biopsy for breast lesions using the handheld vacuum‐assisted core biopsy device in phantoms and patients.

Materials and Methods

Biopsies were done using a 10‐gauge handheld vacuum‐assisted core biopsy system (Vacora, Bard, AZ, USA) on a 1.5T MRI scanner (Philips Achieva, Best, The Netherlands). A standardized biopsy localization protocol was followed by trained operators for multiplanar planning of the biopsy on a separate workstation. Biopsy localization errors were determined as the distance from needle tip to center of the target in three dimensions.

Results

Twenty MRI‐guided biopsies of phantoms were performed by three different operators. The biopsy target mean size was 6.8 ± 0.6 mm. The overall mean three‐dimensional (3D) biopsy targeting error was 4.4 ± 2.9 mm. Thirty‐two MRI breast biopsies performed in 22 patients were reviewed. The lesion mean size was 10.5 ± 9.4 mm. The overall mean 3D localization error was 5.7 ± 3.0 mm. No significant differences between phantom and patients biopsy errors were found (P > 0.5).

Conclusion

MRI‐guided handheld vacuum‐assisted core biopsy device shows good targeting accuracy and should allow localization of lesions to within ～5 to 6 mm. J. Magn. Reson. Imaging 2009;30:424–429. © 2009 Wiley‐Liss, Inc.     

Four-dimensional transcatheter intraarterial perfusion MRI monitoring of radiofrequency ablation of rabbit VX2 liver tumors

Purpose:

To investigate the hypothesis that four‐dimensional (4D) transcatheter intraarterial perfusion (TRIP) magnetic resonance imaging (MRI) can quantify immediate perfusion changes after radiofrequency (RF) ablation in rabbit VX2 liver tumors.

Materials and Methods:

Nine New Zealand White rabbits were used to surgically implant VX2 liver tumors. During ultrasound‐guided RF ablation, tumors received either a true or sham ablation. After selective catheterization of the left hepatic artery under x‐ray fluoroscopy, we acquired pre‐ and post‐RF ablation 4D TRIP MR images using 3 mL of 2.5% intraarterial gadopentetate dimeglumine. Two regions‐of‐interest were drawn upon each tumor to generate signal‐intensity time curves. Area under the curve (AUC) was calculated to provide semiquantitative perfusion measurements that were compared using a paired t‐test (α = 0.05). Ablated tissue was visually confirmed on pathology using Evans blue dye.

Results:

Mean AUC perfusion of VX2 tumors for the true ablation group decreased by 92.0% (95% confidence interval [CI]: 83.3%–100%), from 1913 (95% CI: 1557, 2269) before RF ablation to 76.6 (95% CI: 18.4, 134.8) after RF ablation (a.u., P < 0.001). Sham‐ablated tumors demonstrated no significant perfusion changes.

Conclusion:

4D TRIP MRI can quantify liver tumor perfusion reductions in VX2 rabbits after RF ablation. This MRI technique can potentially be used to improve tumor response assessment at the time of RF ablation. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Rapid freehand MR‐guided percutaneous needle interventions: An image‐based approach to improve workflow and feasibility

Purpose:

To develop and evaluate software‐based methods for improving the workflow of magnetic resonance (MR)‐guided percutaneous interventions.

Materials and Methods:

A set of methods was developed that allows the user to: 1) plan an entire procedure, 2) directly apply this plan to skin entry site localization without further imaging, and 3) place a needle under real‐time MR guidance with automatic alignment of three orthogonal slices along a planned trajectory with preference to the principal patient axes. To validate targeting accuracy and time, phantom experiments (96 targets) and in vivo paraspinal and kidney needle punctures in two pigs (55 targets) were performed. The influence of trajectory obliquity, level of experience, and organ motion on targeting accuracy and time was analyzed.

Results:

Mean targeting error was 1.8 ± 0.9 mm (in vitro) and 2.9 ± 1.0 mm (in vivo) in all directions. No statistically significant differences in targeting accuracy between single‐ and double‐oblique trajectories, novice and expert users, or paraspinal and kidney punctures were observed. The average time (in vivo) from trajectory planning to verification of accurate needle placement was 6 minutes.

Conclusion:

The developed methods allow for accurate needle placement along complex trajectories and are anticipated to reduce table time for MR‐guided percutaneous needle interventions. J. Magn. Reson. Imaging 2013;37:1202–1212. © 2013 Wiley Periodicals, Inc.     

MRI assessment of percutaneous ablation of liver tumors: Value of subtraction images

Purpose:

To evaluate the value of subtraction images when using MRI to assess liver tumors treated with percutaneous ablation.

Materials and Methods:

Following percutaneous ablation of 35 liver tumors, two abdominal radiologists, blinded to outcomes, independently reviewed follow‐up MRI examinations for tumoral enhancement suggestive of residual/recurrent tumor and rated their confidence level. After one year, the readers reviewed the same examinations with added subtraction images. Accuracy of the detection of residual/recurrent tumor and contrast‐to‐noise ratios (CNR; for tumoral enhancement‐to‐liver, tumoral enhancement‐to‐ablation zone, and ablation zone‐to‐liver) were calculated with and without subtraction images and compared using Wilcoxon signed rank test. Interobserver variability was computed using Kappa (κ) statistics.

Results:

Residual/recurrent tumor was present in 8 (23.5%) of 34 tumors. Accuracy of detecting residual/recurrent tumor with subtraction images and interobserver agreement (κ = 0.72, good) were better than accuracy of detecting residual/recurrent tumor and interobserver agreement (κ = 0.57, moderate) of enhanced MR images without subtraction. Mean CNR of subtraction images was significantly higher than that of enhanced MR images for tumoral enhancement‐to‐liver (0.2 ± 5 versus 11.6 ± 14.4, P = 0.03), tumoral enhancement‐to‐ablation zone (10.1 ± 12.5 versus 34.4 ± 29.4, P = 0.02), and ablation zone‐to‐liver (11.8 ± 13.3 versus 102.5 ± 238.4, P = 0.03).

Conclusion:

When using MRI, subtraction images help both detect and exclude residual/recurrent tumor following percutaneous liver ablations. J. Magn. Reson. Imaging 2013;37:407–413. © 2012 Wiley Periodicals, Inc.     

Multiparametric 3T endorectal mri after external beam radiation therapy for prostate cancer

Purpose:

To determine the best combination of magnetic resonance imaging (MRI) parameters for the detection of locally recurrent prostate cancer after external beam radiation therapy.

Materials and Methods:

Our Institutional Review Board approved this study with a waiver of informed consent. Twenty‐six patients with suspected recurrence due to biochemical failure were part of this research. The MR protocol included T2‐weighted, MR spectroscopy, and diffusion‐weighted MRI. Transrectal ultrasound‐guided biopsy was the standard of reference. We used logistic regression to model the probability of a positive outcome and generalized estimating equations to account for clustering. The diagnostic performance of imaging was described using receiver operating characteristic (ROC) curves.

Results:

The area under the ROC curve of MR spectroscopic imaging (MRSI) was 83.0% (95% confidence interval [CI] = 75.5–89.1). The combination of all MR techniques did not significantly improve the performance of imaging beyond the accuracy of MRSI alone, but a trend toward improved discrimination was noted (86.9%; 95% CI = 77.6–93.4; P = 0.09).

Conclusion:

Incorporation of MRSI to T2‐weighted and/or diffusion‐weighted MRI significantly improves the assessment of patients with suspected recurrence after radiotherapy and a combined approach with all three modalities may have the best diagnostic performance. J. Magn. Reson. Imaging 2012;36:430–437. ©2012 Wiley Periodicals, Inc.     

Intraprocedural diffusion‐weighted PROPELLER MRI to guide percutaneous biopsy needle placement within rabbit VX2 liver tumors

Purpose

To test the hypothesis that diffusion‐weighted (DW)‐PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) magnetic resonance imaging (MRI) can be used to guide biopsy needle placement during percutaneous interventional procedures to selectively target viable and necrotic tissues within VX2 rabbit liver tumors.

Materials and Methods

Our institutional Animal Care and Use Committee approved all experiments. In six rabbits implanted with 15 VX2 liver tumors, baseline DW‐PROPELLER images acquired prior to the interventional procedure were used for apparent diffusion coefficient (ADC) measurements. Next, intraprocedural DW‐PROPELLER scans were performed with needle position iteratively adjusted to target viable, necrotic, or intermediate border tissue regions. DW‐PROPELLER ADC measurements at the selected needle tip locations were compared with the percentage of tumor necrosis qualitatively assessed at histopathology.

Results

DW‐PROPELLER images demonstrated intratumoral tissue heterogeneity and clearly depicted the needle tip position within viable and necrotic tumor tissues. Mean ADC measurements within the region‐of‐interest encompassing the needle tip were highly correlated with histopathologic tumor necrotic tissue assessments.

Conclusion

DW‐PROPELLER is an effective method to selectively position the biopsy needle tip within viable and necrotic tumor tissues. The DW‐PROPELLER method may offer an important complementary tool for functional guidance during MR‐guided percutaneous procedures. J. Magn. Reson. Imaging 2009;30:366–373. © 2009 Wiley‐Liss, Inc.     

MR-guided radiofrequency ablation of hepatic malignancies at 1.5 T: initial results

Purpose

To assess the feasibility of magnetic resonance (MR)‐guided radiofrequency ablation (RFA) of hepatic malignancies using a high‐field MR scanner.

Materials and Methods

A total of 10 patients with 14 primary (N = 1) or secondary (N = 13) hepatic malignancies underwent MR‐guided RFA using a closed‐bore 1.5 T MR scanner. Lesion diameters ranged from 2.0 cm to 4.7 cm. RFA was performed using a 200‐W generator in combination with a 3.5‐cm LeVeen electrode applying a standardized energy protocol.

Results

RFA was technically feasible in all patients. Necrosis diameter ranged from 2.5 cm to 6.8 cm. The mean follow‐up period is 12.2 ( 1 - 18 ) months. In nine out of 10 patients, local tumor control was achieved. For this purpose, a second CT‐guided RFA was required in two patients. In four patients, multifocal hepatic tumor progression occurred, with the treated lesion remaining tumor‐free in three of these patients. Two patients showed extrahepatic tumor progression. Four patients remained tumor‐free. No major complications occurred.

Conclusion

MR‐guided RFA of hepatic malignancies in a closed‐bore high‐field MR scanner is technically feasible and safe. It can be advantageous in locations considered unfavorable for CT‐guided puncture or in patients in which iodinated contrast material is contraindicated. J. Magn. Reson. Imaging 2004;19:342–348. © 2004 Wiley‐Liss, Inc.

     

Assessment of vascular remodeling under antiangiogenic therapy using DCE‐MRI and vessel size imaging

Purpose

To assess vascular remodeling in tumors during two different antiangiogenic therapies with dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) and vessel size imaging and to evaluate the vessel size index (VSI) as a novel biomarker of therapy response.

Materials and Methods

In two independent experiments, nude mice bearing human skin squamous cell carcinoma xenografts were treated with a vascular endothelial growth factor (VEGF) inhibitor (bevacizumab) or a multitargeted tyrosine kinase inhibitor (SU11248). Changes in tumor vascularity were assessed by DCE‐MRI and vessel size imaging. DCE‐MRI data were analyzed applying a two‐compartment model (Brix), calculating the parameters Amplitude and k_ep.

Results

For both experiments Amplitude decreased significantly in treated tumors while k_ep did not change significantly. VSI showed controversial results. VSI was significantly increased in SU11248‐treated A431 tumors, whereas no changes were found in bevacizumab‐treated HaCaT‐ras‐A‐5RT3 tumors. Immunohistology confirmed these results and suggest differences in the maturation of tumor vascularization as a possible explanation.

Conclusion

DCE‐MRI and vessel size imaging provide reliable and supplementing biomarkers of antiangiogenic therapy response. The results of both methods are in excellent agreement with histology. Nevertheless, our results also indicate that vascular remodeling is complex and that a uniform response cannot be expected for different tumors and therapies. J. Magn. Reson. Imaging 2009;29:1125–1133. © 2009 Wiley‐Liss, Inc.     

Flow in porous metallic materials: a magnetic resonance imaging study

Purpose

To visualize flow dynamics of analytes inside porous metallic materials with laser‐detected magnetic resonance imaging (MRI).

Materials and Methods

We examine the flow of nuclear‐polarized water in a porous stainless steel cylinder. Laser‐detected MRI utilizes a sensitive optical atomic magnetometer as the detector. Imaging was performed in a remote‐detection mode: the encoding was conducted in the Earth's magnetic field, and detection is conducted downstream of the encoding location. Conventional MRI (7T) was also performed for comparison.

Results

Laser‐detected MRI clearly showed MR images of water flowing through the sample, whereas conventional MRI provided no image.

Conclusion

We demonstrated the viability of laser‐detected MRI at low‐field for studying porous metallic materials, extending MRI techniques to a new group of systems that is normally not accessible to conventional MRI. J. Magn. Reson. Imaging 2008;28:1299–1302. © 2008 Wiley‐Liss, Inc.     

Magnetic resonance imaging and model prediction for thermal ablation of tissue

Purpose

To monitor and predict tissue temperature distributions and lesion boundaries during thermal ablation by combining MRI and thermal modeling methods.

Materials and Methods

Radiofrequency (RF) ablation was conducted in the paraspinal muscles of rabbits with MRI monitoring. A gradient‐recalled echo (GRE) sequence via a 1.5T MRI system provided tissue temperature distribution from the phase images and lesion progression from changes in magnitude images. Post‐ablation GRE estimates of lesion size were compared with post‐ablation T2‐weighted turbo‐spin‐echo (TSE) images and hematoxylin and eosin (H&E)‐stained histological slices. A three‐dimensional (3D) thermal model was used to simulate and predict tissue temperature and lesion size dynamics.

Results

The lesion area estimated from repeated GRE images remained constant during the post‐heating period when the temperature of the lesion boundary was less than a critical temperature. The final lesion areas estimated from multi‐slice (M/S) GRE, TSE, and histological slices were not statistically different. The model‐simulated tissue temperature distribution and lesion area closely corresponded to the GRE‐based MR measurements throughout the imaging experiment.

Conclusion

For normal tissue in vivo, the dynamics of tissue temperature distribution and lesion size during RF thermal ablation can be 1) monitored with GRE phase and magnitude images, and 2) simulated for prediction with a thermal model. J. Magn. Reson. Imaging 2007;26:123–132. © 2007 Wiley‐Liss, Inc.     

Microwave ablation assisted by a real-time virtual navigation system for hepatocellular carcinoma undetectable by conventional ultrasonography

Objectives

To evaluate the efficiency and feasibility of microwave (MW) ablation assisted by a real-time virtual navigation system for hepatocellular carcinoma (HCC) undetectable by conventional ultrasonography.

Methods

18 patients with 18 HCC nodules (undetectable on conventional US but detectable by intravenous contrast-enhanced CT or MRI) were enrolled in this study. Before MW ablation, US images and MRI or CT images were synchronized using the internal markers at the best timing of the inspiration. Thereafter, MW ablation was performed under real-time virtual navigation system guidance. Therapeutic efficacy was assessed by the result of contrast-enhanced imagings after the treatment.

Results

The target HCC nodules could be detected with fusion images in all patients. The time required for image fusion was 8–30 min (mean, 13.3 ± 5.7 min). 17 nodules were successfully ablated according to the contrast enhanced imagings 1 month after ablation. The technique effectiveness rate was 94.44% (17/18). The follow-up time was 3–12 months (median, 6 months) in our study. No severe complications occurred. No local recurrence was observed in any patients.

Conclusions

MW ablation assisted by a real-time virtual navigation system is a feasible and efficient treatment of patients with HCC undetectable by conventional ultrasonography.     

MRI-guided biopsy and fine needle aspiration biopsy (FNAB) in the diagnosis of musculoskeletal lesions

Objectives

The purpose of this study was to evaluate the diagnostic performance of magnetic resonance imaging (MRI) guided musculoskeletal biopsy and the value of fine needle aspiration biopsy (FNAB) when combined with histologic biopsy.

Materials and methods

A total of 172 biopsies were performed under MRI guidance, 170 were histologic biopsies. In 112 cases, a fine needle aspiration biopsy was also performed. In two cases, a stand-alone FNAB was performed. The diagnostic performance was evaluated retrospectively by comparing the histopathologic and cytologic diagnosis with the current or final diagnosis after at least one year of clinical and imaging follow-up. A 0.23 T open MRI scanner with an interventional stereotactic guidance system was used.

Results

The overall diagnostic accuracy of MRI guided biopsy was 0.95, sensitivity 0.91, specificity 0.98, positive predictive value (ppv) 0.97 and negative predictive value (npv) 0.93. The diagnostic accuracy of trephine biopsy alone was 0.93, sensitivity 0.89, specificity 0.98, ppv 0.97 and npv 0.91 and accuracy for FNAB alone was 0.85, sensitivity 0.80, specificity 0.90, ppv 0.89 and npv 0.82.

Conclusions

MRI guidance is a feasible and accurate tool in percutaneous musculoskeletal biopsies. Fine needle biopsy is a useful low-cost supplement to histologic biopsy.     

MR-guided Neurolytic Celiac Plexus Ablation: An Evaluation of Effect and Injection Spread Pattern in Cancer Patients with Celiac Tumor Infiltration

Objective

The purpose of this study was to evaluate the feasibility, the initial accuracy, and the effects of the MR-guided neurolytic celiac plexus ablation as a method to treat cancer-induced chronic abdominal pain.

Methods

Thirteen celiac plexus ablations were performed for 12 patients. A 0.23-T open MRI scanner with optical navigation was used for procedural guidance. As an adjunct to the MR-guided needle positioning, the needle location was confirmed with saline injection and consequent MR imaging (STIR sequence). The spread of the ablative injection material (alcohol-lidocaine mix) was observed by repeating this sequence after the therapeutic injection. Pain scores from seven patients (eight ablations) were used to assess the therapy effect.

Results

MR guidance allowed adequate needle positioning and visualization of injection material in all cases. The rest pain scores significantly decreased from 4 (median) at baseline to 1 (median) at 2 weeks (p < 0.05). Average and worst pain experienced during the past week were significantly lower at the 2-week time point compared with the baseline (p < 0.05). However, the intervention did not result in reduction of opioid use at 2 weeks.

Conclusions

MR guidance is an accurate and safe method for celiac plexus ablation with positive therapeutic effect.     

Potential of magnetization transfer MRI for target volume definition in patients with non‐small‐cell lung cancer

Purpose

To develop a magnetization transfer (MT) module in conjunction with a single‐shot MRI readout technique and to investigate the MT phenomenon in non‐small‐cell lung cancer (NSCLC) as an adjunct for radiation therapy planning.

Materials and Methods

A total of 10 patients with inoperable NSCLC were investigated using a 1.5T MR scanner. MT ratio (MTR) maps of several slices throughout the tumor were assessed. Each MTR‐map was acquired within a short breathhold. Fluorodeoxyglucose positron emission tomography (FDG‐PET) investigations were performed in addition to the MRI protocol. A total of 60 structures appearing conspicuous in FDG‐PET were compared with structures appearing conspicuous in corresponding MTR maps. Quantification of similarity between both modalities was performed using similarity index calculation.

Results

MTR‐maps showed different contrast than FDG‐PET images. However, structures that appeared conspicuous in FDG‐PET images, either by a marked signal enhancement or signal decrease, were found to be similarly present in MTR maps. A mean similarity index of 0.65 was calculated. MTR values of suspected atelectasis were on average lower than MTR values of tumor tissue.

Conclusion

The proposed MT‐MRI technique provides a high MT efficiency, while being robust and fast enough for breathhold acquisition. The results obtained encourage for further exploration of MT‐MRI as an adjunct for radiotherapy planning in NSCLC. J. Magn. Reson. Imaging 2008;28:1417–1424. © 2008 Wiley‐Liss, Inc.     

Changes in apparent diffusion coefficient and T2 relaxation during radiotherapy for prostate cancer

Purpose:

To evaluate regional and temporal changes in apparent diffusion coefficient (ADC) and T₂ relaxation during radiation therapy (RT) in patients with low and intermediate risk localized prostate cancer.

Materials and Methods:

Seventeen patients enrolled on a prospective clinical trial where MRI was acquired every 2 weeks throughout eight weeks of image‐guided prostate IMRT (78 Gy/39 fractions). ADC and T₂ quantification used entire prostate, central gland, benign peripheral zone, and tumor‐dense regions‐of‐interest, and mean values were evaluated for common response trends.

Results:

Overall, the RT responses were greater than volunteer measurement repeatability, and week 6 appeared to be an optimum time‐point for early detection. RT effects on the entire prostate were best detected using ADC (5–7% by week 2, P < 0.0125), effects on peripheral zone were best detected using T₂ (19% reduction at week 6; P = 0.004) and effects on tumors were best detected using ADC (14% elevation at week 6; P = 0.004).

Conclusion:

ADC and T₂ may be candidate biomarkers of early response to RT warranting further investigation against clinical outcomes. J. Magn. Reson. Imaging 2013;37:909–916. © 2012 Wiley Periodicals, Inc.     

Design and development of a prototype endocavitary probe for high-intensity focused ultrasound delivery with integrated magnetic resonance imaging

Purpose

To integrate a high intensity focused ultrasound (HIFU) transducer with an MR receiver coil for endocavitary MR‐guided thermal ablation of localized pelvic lesions.

Materials and Methods

A hollow semicylindrical probe (diameter 3.2 cm) with a rectangular upper surface (7.2 cm × 3.2 cm) was designed to house a HIFU transducer and enable acoustic contact with an intraluminal wall. The probe was distally rounded to ease endocavitary insertion and was proximally tapered to a 1.5‐cm diameter cylindrical handle through which the irrigation tubes (for transducer cooling) and electrical connections were passed. MR compatibility of piezoceramic and piezocomposite transducers was assessed using gradient‐echo (GRE) sequences. The radiofrequency (RF) tuning of identical 6.5 cm × 2.5 cm rectangular receiver coils on the upper surface of the probe was adjusted to compensate for the presence of the conductive components of the HIFU transducers. A T1‐weighted (T1‐W) sliding window dual‐echo GRE sequence monitored phase changes in the focal zone of each transducer. High‐intensity (2400 W/cm^–2), short duration (<1.5 seconds) exposures produced subtherapeutic temperature rises.

Results

For T1‐W images, signal‐to‐noise ratio (SNR) improved by 40% as a result of quartering the conductive surface of the piezoceramic transducer. A piezocomposite transducer showed a further 28% improvement. SNRs for an endocavitary coil in the focal plane of the HIFU trans‐ducer (4 cm from its face) were three times greater than from a phased body array coil. Local shimming improved uniformity of phase images. Phase changes were detected at subtherapeutic exposures.

Conclusion

We combined a HIFU transducer with an MR receiver coil in an endocavitary probe. SNRs were improved by quartering the conductive surface of the piezoceramic. Further improvement was achieved with a piezocomposite transducer. A phase change was seen on MR images during both subtherapeutic and therapeutic HIFU exposures. J. Magn. Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.