Improving the spatial accuracy in functional magnetic resonance imaging (fMRI) based on the blood oxygenation level dependent (BOLD) effect: benefits from parallel imaging and a 32-channel head array coil at 1.5 Tesla

Geometric distortions and low spatial resolution are current limitations in functional magnetic resonance imaging (fMRI). The aim of this study was to evaluate if application of parallel imaging or significant reduction of voxel size in combination with a new 32-channel head array coil can reduce those drawbacks at 1.5 T for a simple hand motor task. Therefore, maximum t-values (tmax) in different regions of activation, time-dependent signal-to-noise ratios (SNR(t)) as well as distortions within the precentral gyrus were evaluated. Comparing fMRI with and without parallel imaging in 17 healthy subjects revealed significantly reduced geometric distortions in anterior-posterior direction. Using parallel imaging, tmax only showed a mild reduction (7-11%) although SNR(t) was significantly diminished (25%). In 7 healthy subjects high-resolution (2 x 2 x 2 mm3) fMRI was compared with standard fMRI (3 x 3 x 3 mm3) in a 32-channel coil and with high-resolution fMRI in a 12-channel coil. The new coil yielded a clear improvement for tmax (21-32%) and SNR(t) (51%) in comparison with the 12-channel coil. Geometric distortions were smaller due to the smaller voxel size. Therefore, the reduction in tmax (8-16%) and SNR(t) (52%) in the high-resolution experiment seems to be tolerable with this coil. In conclusion, parallel imaging is an alternative to reduce geometric distortions in fMRI at 1.5 T. Using a 32-channel coil, reduction of the voxel size might be the preferable way to improve spatial accuracy.

New perfusion imaging of tissue transplants with Contrast Harmonic Ultrasound Imaging (CHI) and Magnetic Resonance Imaging (MRI) in comparison with laser-induced Indocyanine Green (ICG) fluorescence angiography

PURPOSE

Evaluation of post-surgery tissue perfusion of free flaps of the lower leg with contrast enhanced harmonic imaging (CHI), laser-induced indocyanine green (ICG) fluorescence angiography and magnetic resonance imaging (MRI).

MATERIALS AND METHODS

10 patients with free flaps of the lower limb were evaluated with CHI, ICG-fluorescence angiography and perfusion weighted MRI. Perfusion weighted MRI was performed after intravenous bolus injection of 25 ml Gd-DTPA. The ICG fluorescence was detected by a near-infrared-laser device (lambda em = 780 nm). Ultrasound was carried out by an experienced examiner with a linear probe after intravenous bolus injection of 2.4 ml SonoVue. For MRI time intensity curves as well as color-coded blood volume maps of the whole free flap were qualitatively evaluated. For CHI and ICG time intensity curves in selected regions of interest were analyzed. A score from 1-5 (1 = low, 5 = excellent) was used for analysis of perfusion images by three independent readers.

RESULTS

In 3 cases (radialis, parascapular and lateral thigh flap) CHI, MRI and ICG perfusion imaging showed an excellent (score 4-5) contrast enhancement of the cutaneous and subcutaneous part of the free flaps. In 2 cases of osteocutaneous flaps perfusion in central and distal parts of the free flaps was reduced (score 2). Correlation between CHI, MRI and ICG was 0.69-0.83 for the distal parts of the free flaps and 0.74-0.87 for the center of the flaps (Spearman test). Perfusion in the center of the free flaps was significantly different for MRI and ICG and also for MRI and CHI (p<0.05, Wilcoxon test).

CONCLUSION

These first results introduce CHI and MRI perfusion imaging as a promising post-surgery monitoring in patients with free flaps.

BLADE in sagittal T2-weighted MR imaging of the cervical spine

BACKGROUND AND PURPOSE

Image quality and diagnostic reliability of T2-weighted MR images of the cervical spine are often impaired by several kinds of artifacts, even in cooperative patients. The aim of this study was to evaluate if BLADE sequences might solve these problems in a routine patient collective.

MATERIALS AND METHODS

TSE and BLADE sequences were compared in 60 patients for T2-weighted sagittal imaging of the cervical spine. Image sharpness, motion artifacts, truncation artifacts, metal artifacts, CSF flow phenomena, contrast of anatomic structures (vertebral body/disk, spinal cord/CSF), and diagnostic reliability of spinal cord depiction were evaluated by 2 independent readers. Another 2 readers selected the sequence they would prefer for diagnostic purposes. Statistical evaluations were performed by using the Wilcoxon and the chi(2) test; differences with P < .05 were regarded as statistically significant.

RESULTS

BLADE was significantly superior to TSE regarding image sharpness, image contrast, diagnostic reliability of spinal cord depiction, motion artifacts, CSF flow phenomena, and truncation artifacts; for metal artifacts no significant improvements were found. In 50 of 60 patients, BLADE was preferred for diagnostic purposes, and TSE was favored in 3 patients. The number of examinations that were nondiagnostic due to impaired spinal cord depiction was reduced from 12 in TSE to 3 in BLADE, and nondiagnostic examinations due to overall motion artifacts were reduced from 2 to 1.

CONCLUSIONS

Using the BLADE sequence for sagittal T2-weighted imaging of the cervical spine proved to be advantageous to reduce various kinds of artifacts.

A new method to quantify the effect after subcutaneous injection of lipolytic substances

BACKGROUND

Increasing numbers of patients request lipolytic injection therapy for aesthetic indications. However, only the clinical results of these therapies have been published to date. In most cases, pre- and postprocedure photographs and measurements have been presented. As with every other medical procedure, it is necessary to ensure that the results of lipolytic injections are quantified on an objective and scientific basis with comparable data.

METHODS

In the past, the size of fat tissue could not be measured properly with conventional ultrasound systems. High-resolution, real-time three-dimensional (RT-3D) ultrasound is a fairly new method for measuring the volume of tissue. Therefore, this study aimed to measure the interscapular fat bodies of New Zealand rabbits before and after lipolytic therapy with Lipostabil, phosphatidycholine and orciprenalin (Alupent).

RESULTS

The ultrasound-controlled injection of the lipolytic substances into the interscapular fat body ensured a precise injection. The RT-3D ultrasound data were compared with the magnetic resonance imaging (MRI) measurements performed at the same time. The greatest decrease in volume, up to 44%, was measured with orciprenalin (Alupent). There was a significant correlation between the data from ultrasound imaging and MRI.

CONCLUSION

The data suggest that RT-3D ultrasound imaging could be a simple and fast method for proving the effects on volume size after lipolytic procedures. Of the three investigated substances, orciprenalin (Alupent) showed the highest lipolytic effect in our animal model.

Evaluation of carotid artery stenosis with multisection CT and MR imaging: influence of imaging modality and postprocessing

BACKGROUND AND PURPOSE

We prospectively evaluated the influence of different imaging techniques (time-of-flight MR angiography [TOF-MRA], contrast-enhanced MR angiography [CE-MRA], multisection CT angiography [CTA]) and postprocessing methods (maximum intensity projection [MIP], multiplanar reformation [MPR]) on carotid artery stenosis grading.

MATERIALS AND METHODS

Fifty patients (34 men, 16 women) with symptomatic stenosis of the internal carotid artery were examined with a 16-section spiral CT and a 1.5T MR unit. Two MRA techniques were applied: 3D-TOF and CE-MRA. MPR was used for postprocessing with all modalities; MIP was used only with MRA. Four readers measured and calculated the percentage diameter stenosis independently according to NASCET criteria. The Wilcoxon test was used to measure interobserver variability, and the Friedman test was used to test the null-hypothesis of equality of the modalities.

RESULTS

The hypothesis for global equality was rejected (P < .001). TOF-MRA and CTA assessed with MPR showed the highest concordance (difference, 0.6%; confidence interval [CI], -3.0, 4.3%), and CE-MRA with MIP and CTA showed the lowest concordance in stenosis grading (difference, 7.0%; CI, 3.4, 10.6%). MPR resulted in lower degrees of stenosis than MIP for both MRA sequences, although not statistically significant (CE, -3.0%; CI, -6.6, 0.6%; TOF, -2.2%; CI, -5.8, 1.4%). When only studies with good or excellent image quality were considered, the differences decreased, but the trends remained.

CONCLUSION

Stenosis grading is dependent on the examination method and postprocessing technique. CTA and TOF-MRA evaluated with MPR revealed highest concordance.

Magnetic Resonance Angiography of the Peripheral Vessels in Patients with Peripheral Arterial Occlusive Disease: When Is an Additional Conventional Angiography Required?

The purpose of this work was to find out how often the clinician asks for a conventional angiography (CA) in patients with peripheral arterial occlusive disease (PAOD) after a magnetic resonance angiography (MRA) has been performed and how often the CA reveals additional information for therapy planning. Quality criteria for the MRA were defined and tested to see whether they can predict the need for an additional CA. In this prospective study, 81 patients suffering from PAOD (Fontaine classification IIa, n = 13; IIb, n = 33; III, n = 10; IV, n = 25) were examined with a 1.5-T MR-scanner with dedicated coils using a step-by-step technique. The vascular surgeon decided whether he could plan the therapy on the basis of the MRA or if he needed an additional CA. The MRA was assessed in terms of the image quality of the MRA and regarding therapeutic management of the patient in a two-grade scale: sufficient and insufficient. In 27/81 (33%) patients, the clinician asked for a CA, which revealed new information in only 11 patients. The relative number of MRAs with insufficient image quality was significantly higher (p < 0.01) in the group with additional information on CA (8/11) compared to the group without additional information (0/16). The assessment of an MRA based on image quality and regarding therapeutic management of the patient might reduce the number of CAs for therapy planning in patients with PAOD.

Cortical T2 signal shortening in amyotrophic lateral sclerosis is not due to iron deposits

Signal shortening of the motor cortex in T2-weighted MR images is a frequent finding in patients with amyotrophic lateral sclerosis (ALS). The cause of signal shortening in ALS is unknown, although iron deposits have been suggested. To test this hypothesis, we acquired T2*-weighted gradient-echo (GRE) MR images in addition to T2-weighted turbo spin-echo in 69 patients with ALS. Signal shortening in T2-weighted images was found in 31 patients. In T2*-weighted GRE images, only three patients had signal shortening. One patient with additional bifrontal haemorrhage had frontal but no motor cortex signal shortening. Iron deposits do not cause cortical signal shortening in patients with ALS predominantly. Other factors are presumably more important in the generation of cortical T2 shortening in ALS.

Carotid artery calcium: accuracy of a calcium score by computed tomography-an in vitro study with comparison to sonography and histology

OBJECTIVES

The aim of this study was to compare methods of quantifying calcification of the internal carotid artery.

MATERIALS AND METHODS

We examined 92 internal carotid artery endarterectomy specimens. Grey scale median (GSM) values were calculated from optimized B-mode scans. The degree of calcification was assessed using radiographic calcification grading. Plaques were processed histologically, and classified into: (1) calcium-rich hard plaques, (2) lipid-rich soft plaques, and (3) combined plaques. The specimens were scanned in CT-scanner. The calcium score was determined as described by Agatston.

RESULTS

Histopathology and GSM results concurred in 39 out of 92 cases (kappa=0.088). There was no significant correlation between the calcium score and the median GSM value (R=0.005; P=0.959). Histology and CT morphology showed a significant concordance (P<0.001). Also CT and radiomorphological classification showed close agreement (R=0.628, P<0.001).

CONCLUSIONS

Calcium scores calculated using CT morphology enable precise in vitro evaluation of the calcium content of plaques in the internal carotid. In contrast, grey scale median values do not adequately reflect calcification of plaques.

Hyperintense and hypointense MRI signals of the precentral gyrus and corticospinal tract in ALS: a follow-up examination including FLAIR images

In amyotrophic lateral sclerosis (ALS) patients, hyperintense signals at the subcortical precentral gyrus in brain fluid attenuated inversion recovery (FLAIR) MR images have been found more frequently than in controls. Quantitative analysis has revealed a significant increase of the FLAIR-magnetic resonance imaging (MRI) signal at the subcortical precentral gyrus of ALS patients compared to healthy controls. In addition, hypointense signals at the rim of the precentral gyrus in FLAIR and T2-weighted images have been shown in ALS patients. In 17 ALS patients, we evaluated hyperintense signals in T2-, T1-, proton density-weighted and FLAIR MR images, and hypointense signals in T2-weighted and FLAIR images 15.7+/-3.0 months after the initial examination by visual scoring. In FLAIR images, a quantitative analysis was added. The visual scores of hyperintense signals along the corticospinal tract did not change significantly in all sequences. However, the quantitative evaluation of FLAIR images revealed a significant increase of the signal intensity at the subcortical precentral gyrus (p<0.005). In addition, the frequency of the visually evaluated hypointense signals at the precentral gyrus increased significantly (p<0.05). The change of MR results did not correlate with the change of clinical parameters. In ALS patients, the increase of the quantified MRI signal at the subcortical precentral gyrus in FLAIR images and the increase of hypointense signals at the rim of the precentral gyrus corroborate the hypothesis that these signals are related to the upper motor neuron degeneration in ALS. Their specificity and clinical relevance have to be clarified further.

Direct MR arthrography of the shoulder: 2D vs. 3D gradient-echo imaging

The aim of this study was to determine the value of a fat suppressed 3D gradient-echo sequence (GRE) data set in comparison to a 2D GRE sequence in direct MR arthrography of the shoulder. For this purpose we examined 50 consecutive patients with subacute or chronic disorders of the shoulder using a 1.5 T scanner: Transverse T1-weighted 2D (slice thickness 4 mm) and 3D GRE (slice thickness 1.5 mm reconstructed from 3 mm), oblique coronal T2- and T1-weighted turbo spin-echo (TSE) and sagittal T1-weighted TSE with fat saturation were applied. Visual image analysis of anatomical and pathological structures was performed by two independent observers. A correlation to surgical results was available in 21 patients. Transverse GRE sequences were well suited for analysis of the anterior/posterior labrum, the middle glenohumeral ligament, and cartilage. 3D GRE with fat suppression was slightly superior to 2D GRE without fat suppression in the evaluation of the anterior/posterior labrum, and the middle glenohumeral ligament, whereas for cartilage no significant differences were found between both sequences. Concerning pathological findings, in most of the cases 2D delivered the same results as 3D. In conclusion, a T1-weighted 3D GRE data set with fat saturation in transverse orientation may be useful for evaluation of the anterior/posterior labrum, and the middle glenohumeral ligament. However, similar measured slice thickness of 3 mm-even if interpolated to 1.5 mm-compared to a 2D sequence with 4 mm does not provide significant diagnostic advantages.

Endovascular brachytherapy for prophylaxis against restenosis after long-segment femoropopliteal placement of stents: initial results

PURPOSE

To evaluate the feasibility, safety, and effectiveness of endovascular brachytherapy for the prevention of restenosis after long-segment femoropopliteal percutaneous transluminal angioplasty (PTA) and stent implantation.

MATERIALS AND METHODS

Thirty-three patients (23 men, 10 women; mean age, 66 years) with femoropopliteal lesions (mean treated length, 17 cm; range, 4-30 cm) underwent PTA and stent implantation followed by brachytherapy with a centering catheter. A dose of 14 Gy was delivered to the adventitia by using an iridium 192 source. Long-term pharmacotherapy with acetylsalicylic acid was combined with clopidogrel for 1 month. Follow-up examinations included measurement of the ankle-brachial index, color-coded duplex ultrasonography, and angiography.

RESULTS

The overall 6-month recurrence rate was 30% (10 of 33 arteries). Seven patients developed sudden late thrombotic occlusion of the segment with the stent 3.5-6 months after stent implantation. Considering the overall results after successful local thrombolysis in six of these seven patients, only four (12%) of 33 arteries with a stent had in-stent restenosis caused by neointimal hyperplasia.

CONCLUSION

The study results are promising concerning the possibility of reducing in-stent restenosis by means of brachytherapy after long-segment femoropopliteal placement of stents. The high incidence of late thrombotic occlusion requires optimization of the antithrombotic regimen.

Intraluminal 192Ir brachytherapy following transjugular intrahepatic portosystemic shunt revision: long-term results and radiotherapy parameters

PURPOSE

The stenosis or occlusion of transjugular intrahepatic portosystemic shunt (TIPS) occurs in up to 75% of patients within 12 months after treatment. The aim of our investigation was to evaluate the feasibility, safety and efficacy of intraluminal high-dose rate brachytherapy (HDRBT) with Iridium-192 following TIPS revision to prevent restenosis due to pseudointimal hyperplasia.

MATERIALS AND METHODS

Between September and November 1996, intraluminal BT was performed in five patients after TIPS revision. The indications for initial TIPS were a Budd-Chiari syndrome in two female patients and recurrent variceal bleeding by alcoholic liver cirrhosis in three male patients. TIPS was created with Wallstents (10 mm diameter in four patients) and Palmaz stent (10 mm diameter in one patient). The re-dilatation was done in all five patients 6 months after first stenting because of restenosis (>50% stent lumen reduction) or occlusion of the stent. A 5-French closed-tip, noncentered BT delivery catheter was used for subsequent radiotherapy. The whole length of the stent and performed dilatation (interventional length - IL) was taken as clinical target length (CTL). A 10-mm safety margin was added proximal and distal to the CTL due to uncertainties of BT source positioning, so forming the planning target length (PTL). To ensure that prescribed dose covers the whole PTL, the active source length (ASL) was 5 mm longer proximal and distal than PTL, so forming the reference isodose length (RIL). A dose of 12 Gy was prescribed in 3 mm distance from the source axis in the mid-plane of the applicator for three patients and in 5 mm distance for two patients.

RESULTS

A normal patency (<50% lumen reduction) of the stent was achieved at 44 months follow-up (duplex sonography+portography) in all three patients with liver cirrhosis, whereas further revisions were necessary in two patients with Budd-Chiari syndrome (after 5.5 and 18 months). No acute, subacute or late brachytherapy (BT)-related side effects were seen until now.

CONCLUSIONS

HDRBT following TIPS revision was safe and feasible in all patients. The exact impact of BT on the TIPS patency should be evaluated in larger clinical trials. Moderate dose escalation and use of today's commercially available centering radiation catheters seem to be necessary.