Multidimensionally encoded magnetic resonance imaging

Magnetic resonance imaging (MRI) typically achieves spatial encoding by measuring the projection of a q‐dimensional object over q‐dimensional spatial bases created by linear spatial encoding magnetic fields (SEMs). Recently, imaging strategies using nonlinear SEMs have demonstrated potential advantages for reconstructing images with higher spatiotemporal resolution and reducing peripheral nerve stimulation. In practice, nonlinear SEMs and linear SEMs can be used jointly to further improve the image reconstruction performance. Here, we propose the multidimensionally encoded (MDE) MRI to map a q‐dimensional object onto a p‐dimensional encoding space where p > q. MDE MRI is a theoretical framework linking imaging strategies using linear and nonlinear SEMs. Using a system of eight surface SEM coils with an eight‐channel radiofrequency coil array, we demonstrate the five‐dimensional MDE MRI for a two‐dimensional object as a further generalization of PatLoc imaging and O‐space imaging. We also present a method of optimizing spatial bases in MDE MRI. Results show that MDE MRI with a higher dimensional encoding space can reconstruct images more efficiently and with a smaller reconstruction error when the k‐space sampling distribution and the number of samples are controlled. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

On the Relationship Between Feature-Recognizing MRI and MRI Encoded by Singular Value Decomposition

This paper describes the similarity between two methods of non-Fourier MRI: feature-recognizing MRI (FR MRI) and MRI with encoding by singular value decomposition (SVD MRI). Both methods represented images as truncated expansions of non-Fourier basis functions; these basis images were derived from prior image data by using closely-related mathematical techniques: the Karhunen-Loeve decomposition (or principal components analysis) and singular value decomposition, respectively. We demonstrate that FR and SVD MRI are equivalent in the following sense: given the same prior image data, they lead to exactly the same basis functions. FR MRI utilized prior images of the same body part in many “training” subjects, thought to be similar to the “unknown” subject to be imaged. SVD MRI utilized a single prior image of one subject in order to perform dynamic imaging of that subject. We demonstrate that the basis function expansion derived from a single prior image may not be capable of representing new features (features not found in the prior image). Therefore, the SVD basis functions may be inappropriate for dynamic imaging.     

Adaptive keyhole methods for dynamic magnetic resonance image reconstruction.

Dynamic magnetic resonance imaging (MRI) acquires a sequence of images for the visualization of the temporal variation of tissue or organs. Keyhole methods such as Fourier keyhole (FK) and keyhole SVD (KSVD) are the most popular methods for image reconstruction in dynamic MRI. This paper provides a class of adaptive keyhole methods, called adaptive FK (AFK) and adaptive KSVD (AKSVD), for dynamic MRI reconstruction. The proposed methods are based on the conventional Fourier encoding and SVD encoding schemes. Instead of the conventional keyhole methods' duplication of un-acquired data from the reference images, the proposed methods use a temporal model to depict the inter-frame dynamic changes and to estimate the un-acquired data in each successive frame. Because the model is online identified from the acquired data, the proposed methods do not require the pre-imaging process, the navigator signals, and any prior knowledge of the imaged objects. Furthermore, the new methods use the conventional keyhole encoding schemes without the bias to any particular object characters, and the temporal model for updating information is in the general form of AR process without the preference to any particular motion types. Hence, the proposed methods are designed as a generic approach to dynamic MRI, other than for any specific class of objects. Studies on dynamic MRI data set show that the new methods can produce images with much lower reconstruction error than the conventional FK and KSVD.     

Dynamically adaptive MRI with encoding by singular value decomposition

A new MRI spatial encoding method based upon the singular value decomposition (SVD) and using spatially selective RF excitation is described. This encoding technique is particularly; applicable to dynamic adaptive MRI, because it provides a near minimal set of spatial encoding profiles computed using an image estimate that is determined from a previously obtained image. Experimental results are presented for two cases, which exemplify its potential use in different dynamic imaging tasks. SVD-encoded MRI has demonstrated to be a highly efficient encoding scheme.     

Combination of compressed sensing and parallel imaging for highly accelerated first‐pass cardiac perfusion MRI

First‐pass cardiac perfusion MRI is a natural candidate for compressed sensing acceleration since its representation in the combined temporal Fourier and spatial domain is sparse and the required incoherence can be effectively accomplished by k‐t random undersampling. However, the required number of samples in practice (three to five times the number of sparse coefficients) limits the acceleration for compressed sensing alone. Parallel imaging may also be used to accelerate cardiac perfusion MRI, with acceleration factors ultimately limited by noise amplification. In this work, compressed sensing and parallel imaging are combined by merging the k‐t SPARSE technique with sensitivity encoding (SENSE) reconstruction to substantially increase the acceleration rate for perfusion imaging. We also present a new theoretical framework for understanding the combination of k‐t SPARSE with SENSE based on distributed compressed sensing theory. This framework, which identifies parallel imaging as a distributed multisensor implementation of compressed sensing, enables an estimate of feasible acceleration for the combined approach. We demonstrate feasibility of 8‐fold acceleration in vivo with whole‐heart coverage and high spatial and temporal resolution using standard coil arrays. The method is relatively insensitive to respiratory motion artifacts and presents similar temporal fidelity and image quality when compared to Generalized autocalibrating partially parallel acquisitions (GRAPPA) with 2‐fold acceleration. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Evaluation of sampling density on the accuracy of aortic pulse wave velocity from velocity‐encoded MRI in patients with Marfan syndrome

Purpose:

To evaluate the effect of spatial (ie, number of sampling locations along the aorta) and temporal sampling density on aortic pulse wave velocity (PWV) assessment from velocity‐encoded MRI in patients with Marfan syndrome (MFS).

Materials and Methods:

Twenty‐three MFS patients (12 men, mean age 36 ± 14 years) were included. Three PWV‐methods were evaluated: 1) reference PWV_i.p. from in‐plane velocity‐encoded MRI with dense temporal and spatial sampling; 2) conventional PWV_t.p. from through‐plane velocity‐encoded MRI with dense temporal but sparse spatial sampling at three aortic locations; 3) EPI‐accelerated PWV_t.p. with sparse temporal but improved spatial sampling at five aortic locations with acceleration by echo‐planar imaging (EPI).

Results:

Despite inferior temporal resolution, EPI‐accelerated PWV_t.p. showed stronger correlation (r = 0.92 vs. r = 0.65, P = 0.03) with reference PWV_i.p. in the total aorta, with less error (8% vs. 16%) and variation (11% vs. 27%) as compared to conventional PWV_t.p.. In the aortic arch, correlation was comparable for both EPI‐accelerated and conventional PWV_t.p. with reference PWV_i.p. (r = 0.66 vs. r = 0.67, P = 0.46), albeit 92% scan‐time reduction by EPI‐acceleration.

Conclusion:

Improving spatial sampling density by adding two acquisition planes along the aorta results in more accurate PWV assessment, even when temporal resolution decreases. For regional PWV assessment in the aortic arch, EPI‐accelerated and conventional PWV assessment are comparably accurate. Scan‐time reduction makes EPI‐accelerated PWV assessment the preferred method of choice. J. Magn. Reson. Imaging 2012; 36:1470–1476. © 2012 Wiley Periodicals, Inc.     

A comparison of RIGR and SVD dynamic imaging methods

Several constrained imaging methods have recently been proposed for dynamic imaging applications. This paper compares two of these methods: the Reduced-encoding Imaging by Generalized-series Reconstruction (RIGR) and Singular Value Decomposition (SVD) methods. RIGR utilizes a priori data for optimal image reconstruction whereas the SVD method seeks to optimize data acquisition. However, this study shows that the existing SVD encoding method tends to bias the data acquisition scheme toward reproducing the known features in the reference image. This characteristic of the SVD encoding method reduces its capability to capture new image features and makes it less suitable than RIGR for dynamic imaging applications.     

Highly accelerated real‐time cardiac cine MRI using k–t SPARSE‐SENSE

For patients with impaired breath‐hold capacity and/or arrhythmias, real‐time cine MRI may be more clinically useful than breath‐hold cine MRI. However, commercially available real‐time cine MRI methods using parallel imaging typically yield relatively poor spatio‐temporal resolution due to their low image acquisition speed. We sought to achieve relatively high spatial resolution (～2.5 × 2.5 mm²) and temporal resolution (～40 ms), to produce high‐quality real‐time cine MR images that could be applied clinically for wall motion assessment and measurement of left ventricular function. In this work, we present an eightfold accelerated real‐time cardiac cine MRI pulse sequence using a combination of compressed sensing and parallel imaging (k‐t SPARSE‐SENSE). Compared with reference, breath‐hold cine MRI, our eightfold accelerated real‐time cine MRI produced significantly worse qualitative grades (1–5 scale), but its image quality and temporal fidelity scores were above 3.0 (adequate) and artifacts and noise scores were below 3.0 (moderate), suggesting that acceptable diagnostic image quality can be achieved. Additionally, both eightfold accelerated real‐time cine and breath‐hold cine MRI yielded comparable left ventricular function measurements, with coefficient of variation <10% for left ventricular volumes. Our proposed eightfold accelerated real‐time cine MRI with k–t SPARSE‐SENSE is a promising modality for rapid imaging of myocardial function. J. Magn. Reson. Imaging 2013. © 2012 Wiley Periodicals, Inc.     

Spatially encoded phase‐contrast MRI—3D MRI movies of 1D and 2D structures at millisecond resolution

This work demonstrates that the principles underlying phase‐contrast MRI may be used to encode spatial rather than flow information along a perpendicular dimension, if this dimension contains an MRI‐visible object at only one spatial location. In particular, the situation applies to 3D mapping of curved 2D structures which requires only two projection images with different spatial phase‐encoding gradients. These phase‐contrast gradients define the field of view and mean spin‐density positions of the object in the perpendicular dimension by respective phase differences. When combined with highly undersampled radial fast low angle shot (FLASH) and image reconstruction by regularized nonlinear inversion, spatial phase‐contrast MRI allows for dynamic 3D mapping of 2D structures in real time. First examples include 3D MRI movies of the acting human hand at a temporal resolution of 50 ms. With an even simpler technique, 3D maps of curved 1D structures may be obtained from only three acquisitions of a frequency‐encoded MRI signal with two perpendicular phase encodings. Here, 3D MRI movies of a rapidly rotating banana were obtained at 5 ms resolution or 200 frames per second. In conclusion, spatial phase‐contrast 3D MRI of 2D or 1D structures is respective two or four orders of magnitude faster than conventional 3D MRI. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Effect of improving spatial or temporal resolution on image quality and quantitative perfusion assessment with k‐t SENSE acceleration in first‐pass CMR myocardial perfusion imaging

k‐t Sensitivity‐encoded (k‐t SENSE) acceleration has been used to improve spatial resolution, temporal resolution, and slice coverage in first‐pass cardiac magnetic resonance myocardial perfusion imaging. This study compares the effect of investing the speed‐up afforded by k‐t SENSE acceleration in spatial or temporal resolution. Ten healthy volunteers underwent adenosine stress myocardial perfusion imaging using four saturation‐recovery gradient echo perfusion sequences: a reference sequence accelerated by sensitivity encoding (SENSE), and three k‐t SENSE–accelerated sequences with higher spatial resolution (“k‐t High”), shorter acquisition window (“k‐t Fast”), or a shared increase in both parameters (“k‐t Hybrid”) relative to the reference. Dark‐rim artifacts and image quality were analyzed. Semiquantitative myocardial perfusion reserve index (MPRI) and Fermi‐derived quantitative MPR were also calculated. The k‐t Hybrid sequence produced highest image quality scores at rest (P = 0.015). Rim artifact thickness and extent were lowest using k‐t High and k‐t Hybrid sequences (P < 0.001). There were no significant differences in MPRI and MPR values derived by each sequence. Maximizing spatial resolution by k‐t SENSE acceleration produces the greatest reduction in dark rim artifact. There is good agreement between k‐t SENSE and standard acquisition methods for semiquantitative and fully quantitative myocardial perfusion analysis. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

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.     

Superelliptical insert gradient coil with a field‐modifying layer for breast imaging

Many MRI applications such as dynamic contrast‐enhanced MRI of the breast require high spatial and temporal resolution and can benefit from improved gradient performance, e.g., increased gradient strength and reduced gradient rise time. The improved gradient performance required to achieve high spatial and temporal resolution for this application may be achieved by using local insert gradients specifically designed for a target anatomy. Current flat gradient systems cannot create an imaging volume large enough to accommodate both breasts; further, their gradient fields are not homogeneous, dropping off rapidly with distance from the gradient coil surface. To attain an imaging volume adequate for bilateral breast MRI, a planar local gradient system design has been modified into a superellipse shape, creating homogeneous gradient volumes that are 182% (G_x), 57% (G_y), and 75% (G_z) wider (left/right direction) than those of the corresponding standard planar gradient. Adding an additional field‐modifying gradient winding results in an additional improvement of the homogeneous gradient field near the gradient coil surface over the already enlarged homogeneous gradient volumes of the superelliptical gradients (67%, 89%, and 214% for G_x, G_y, and G_z respectively). A prototype y‐gradient insert has been built to demonstrate imaging and implementation characteristics of the superellipse gradient in a 3 T MRI system. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Progression of experimental lesions of atherosclerosis: Assessment by kinetic modeling of black‐blood dynamic contrast‐enhanced MRI

Pharmacokinetic modeling of dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI) is used to noninvasively characterize neovasculature and inflammation in atherosclerotic vessels by estimating perfusion characteristics, such as fractional plasma volume v_p and transfer constant K^trans. DCE‐MRI has potential to study the evolution of nascent lesions involving early pathological changes. However, currently used bright‐blood DCE‐MRI approaches are difficult to apply to small lesions because of the difficulty in separating the signal in the thin vessel wall from the adjacent lumen. By suppressing the lumen signal, black‐blood DCE‐MRI techniques potentially provide a better tool for early atherosclerotic lesion assessment. However, whether black‐blood DCE‐MRI can detect temporal changes in physiological kinetic parameters has not been investigated for atherosclerosis. This study of balloon‐injured New Zealand White rabbits used a reference‐region‐based pharmacokinetic model of black‐blood DCE‐MRI to evaluate temporal changes in early experimental atherosclerotic lesions of the abdominal aorta. Six rabbits were imaged at 3 and 6 months after injury. K^trans was found to increase from 0.10 ± 0.03 min^?1 to 0.14 ± 0.05 min^?1 (P = 0.01). In histological analysis of all twelve rabbits, K^trans showed a significant correlation with macrophage content (R = 0.70, P =0.01). These results suggest black‐blood DCE‐MRI and a reference‐region kinetic model could be used to study plaque development and therapeutic response in vivo. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

A 2D MTF approach to evaluate and guide dynamic imaging developments

As the number and complexity of partially sampled dynamic imaging methods continue to increase, reliable strategies to evaluate performance may prove most useful. In the present work, an analytical framework to evaluate given reconstruction methods is presented. A perturbation algorithm allows the proposed evaluation scheme to perform robustly without requiring knowledge about the inner workings of the method being evaluated. A main output of the evaluation process consists of a two‐dimensional modulation transfer function, an easy‐to‐interpret visual rendering of a method's ability to capture all combinations of spatial and temporal frequencies. Approaches to evaluate noise properties and artifact content at all spatial and temporal frequencies are also proposed. One fully sampled phantom and three fully sampled cardiac cine datasets were subsampled (R = 4 and 8) and reconstructed with the different methods tested here. A hybrid method, which combines the main advantageous features observed in our assessments, was proposed and tested in a cardiac cine application, with acceleration factors of 3.5 and 6.3 (skip factors of 4 and 8, respectively). This approach combines features from methods such as k‐t sensitivity encoding, unaliasing by Fourier encoding the overlaps in the temporal dimension‐sensitivity encoding, generalized autocalibrating partially parallel acquisition, sensitivity profiles from an array of coils for encoding and reconstruction in parallel, self, hybrid referencing with unaliasing by Fourier encoding the overlaps in the temporal dimension and generalized autocalibrating partially parallel acquisition, and generalized autocalibrating partially parallel acquisition–enhanced sensitivity maps for sensitivity encoding reconstructions. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

SEMAC: Slice encoding for metal artifact correction in MRI

Magnetic resonance imaging (MRI) near metallic implants remains an unmet need because of severe artifacts, which mainly stem from large metal‐induced field inhomogeneities. This work addresses MRI near metallic implants with an innovative imaging technique called “Slice Encoding for Metal Artifact Correction” (SEMAC). The SEMAC technique corrects metal artifacts via robust encoding of each excited slice against metal‐induced field inhomogeneities. The robust slice encoding is achieved by extending a view‐angle‐tilting (VAT) spin‐echo sequence with additional z‐phase encoding. Although the VAT compensation gradient suppresses most in‐plane distortions, the z‐phase encoding fully resolves distorted excitation profiles that cause through‐plane distortions. By positioning all spins in a region‐of‐interest to their actual spatial locations, the through‐plane distortions can be corrected by summing up the resolved spins in each voxel. The SEMAC technique does not require additional hardware and can be deployed to the large installed base of whole‐body MRI systems. The efficacy of the SEMAC technique in eliminating metal‐induced distortions with feasible scan times is validated in phantom and in vivo spine and knee studies. Magn Reson Med 62:66–76, 2009. © 2009 Wiley‐Liss, Inc.     

Simultaneously driven linear and nonlinear spatial encoding fields in MRI

Spatial encoding in MRI is conventionally achieved by the application of switchable linear encoding fields. The general concept of the recently introduced PatLoc (Parallel Imaging Technique using Localized Gradients) encoding is to use nonlinear fields to achieve spatial encoding. Relaxing the requirement that the encoding fields must be linear may lead to improved gradient performance or reduced peripheral nerve stimulation. In this work, a custom‐built insert coil capable of generating two independent quadratic encoding fields was driven with high‐performance amplifiers within a clinical MR system. In combination with the three linear encoding fields, the combined hardware is capable of independently manipulating five spatial encoding fields. With the linear z‐gradient used for slice‐selection, there remain four separate channels to encode a 2D‐image. To compare trajectories of such multidimensional encoding, the concept of a local k‐space is developed. Through simulations, reconstructions using six gradient‐encoding strategies were compared, including Cartesian encoding separately or simultaneously on both PatLoc and linear gradients as well as two versions of a radial‐based in/out trajectory. Corresponding experiments confirmed that such multidimensional encoding is practically achievable and demonstrated that the new radial‐based trajectory offers the PatLoc property of variable spatial resolution while maintaining finite resolution across the entire field‐of‐view. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Improving temporal resolution of pulmonary perfusion imaging in rats using the partially separable functions model

Dynamic contrast‐enhanced MRI (or DCE‐MRI) is a useful tool for measuring blood flow and perfusion, and it has found use in the study of pulmonary perfusion in animal models. However, DCE‐MRI experiments are difficult in small animals such as rats. A recently developed method known as Interleaved Radial Imaging and Sliding window‐keyhole (IRIS) addresses this problem by using a data acquisition scheme that covers ( k ,t)‐space with data acquired from multiple bolus injections of a contrast agent. However, the temporal resolution of IRIS is limited by the effects of temporal averaging inherent in the sliding window and keyhole operations. This article describes a new method to cover ( k ,t)‐space based on the theory of partially separable functions (PSF). Specifically, a sparse sampling of ( k ,t)‐space is performed to acquire two data sets, one with high‐temporal resolution and the other with extended k‐space coverage. The high‐temporal resolution training data are used to determine the temporal basis functions of the PSF model, whereas the other data set is used to determine the spatial variations of the model. The proposed method was validated by simulations and demonstrated by an experimental study. In this particular study, the proposed method achieved a temporal resolution of 32 msec. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Combining two‐dimensional spatially selective RF excitation,parallel imaging,and UNFOLD for accelerated MR thermometry imaging

MR thermometry can be a very challenging application, as good resolution may be needed along spatial, temporal, and temperature axes. Given that the heated foci produced during thermal therapies are typically much smaller than the anatomy being imaged, much of the imaged field‐of‐view is not actually being heated and may not require temperature monitoring. In this work, many‐fold improvements were obtained in terms of temporal resolution and/or 3D spatial coverage by sacrificing some of the in‐plane spatial coverage. To do so, three fast‐imaging approaches were jointly implemented with a spoiled gradient echo sequence: (1) two‐dimensional spatially selective RF excitation, (2) unaliasing by Fourier encoding the overlaps using the temporal dimension (UNFOLD), and (3) parallel imaging. The sequence was tested during experiments with focused ultrasound heating in ex vivo tissue and a tissue‐mimicking phantom. Temperature maps were estimated from phase‐difference images based on the water proton resonance frequency shift. Results were compared to those obtained from a spoiled gradient echo sequence sequence, using a t‐test. Temporal resolution was increased by 24‐fold, with temperature uncertainty less than 1°C, while maintaining accurate temperature measurements (mean difference between measurements, as observed in gel = 0.1°C ± 0.6; R = 0.98; P > 0.05). Magn Reson Med 66:112–122, 2011. © 2011 Wiley‐Liss, Inc.     

Application of k‐space energy spectrum analysis for inherent and dynamic B0 mapping and deblurring in spiral imaging

Spiral imaging is vulnerable to spatial and temporal variations of the amplitude of the static magnetic field (B₀) caused by susceptibility effects, eddy currents, chemical shifts, subject motion, physiological noise, and system instabilities, resulting in image blurring. Here, a novel off‐resonance correction method is proposed to address these issues. A k‐space energy spectrum analysis algorithm is first applied to inherently and dynamically generate a B₀ map from the k‐space data at each time point, without requiring any additional data acquisition, pulse sequence modification, or phase unwrapping. A simulated phase evolution rewinding algorithm and an automatic residual deblurring algorithm are then used to correct for the blurring caused by both spatial and temporal B₀ variations, resulting in a high spatial and temporal fidelity. This method is validated against conventional B₀ mapping and deblurring methods, and its advantages for dynamic MRI applications are demonstrated in functional MRI studies. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Inter-modality comparisons of seizure focus lateralization in complex partial seizures

Anterior temporal lobectomy offers a high chance of seizure-free outcome in patients suffering from drug-refractory complex partial seizure (CPS) originating from the temporal lobe. Other than EEG, several functional and morphologic imaging methods are used to define the spatial seizure origin. The present study was undertaken to compare the merits of fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET), magnetic resonance imaging (MRI) and single-voxel proton MR spectroscopy (MRS) for the lateralization of temporal lobe seizure foci. The clinical charts and imaging data of 43 consecutive CPS patients were reviewed. Based on surface EEG, 31 patients were classified with temporal lobe epilepsy (TLE; 25 lateralized, 6 not lateralized) and 12 with non-temporal lobe epilepsy. All were examined by FDG-PET, MRS and MRI within 6 weeks. FDG-PET and MRI were interpreted visually, while the N-acetyl-aspartate to creatine ratio was used for MRS interpretation. One FDG-PET scan was invalid due to seizure activity post injection. The MR spectra could not be evaluated in five cases bilaterally and three cases unilaterally for technical reasons. A total of 15 patients underwent anterior temporal lobectomy. All showed a beneficial postoperative outcome. When the proportions of agreement between FDG-PET (0.77), MRI (0.58) and MRS (0.56) and surface EEG in TLE cases were compared, there were no significant differences (P>0.10). However, FDG-PET showed a significantly higher agreement (0.93) than MRI (0.60; P=0.03) with the side of successful temporal lobectomy. The concordance of MRS with the side of successful temporal lobectomy was intermediate (0.75). When the results of functional and morphologic imaging were combined, no significant differences were found between the rates of agreement of FDG-PET/MRI and MRS/MRI with EEG (0.80 vs 0.68; P=0.50) and with the side of successful temporal lobectomy (0.87 vs 0.92; P=0.50) in TLE cases. However, MRS/MRI showed significantly more lateralized temporal lobe abnormalities in non-temporal lobe epilepsy cases than FDG-PET/MRI (0.90 vs. 0.17; P<0.01). Although FDG-PET seems to be the most reliable and stable method for this purpose, we conclude that in TLE cases it may be justified to perform MRS, which is less expensive, faster and has no radiation exposure, in combination with MRI before FDG-PET, since FDG-PET offers little additional diagnostic information if MRS and MRI indicate the same seizure focus lateralization.