Thermal lesion conspicuity following interstitial radiofrequency thermal tumor ablation in humans: A comparison of STIR, turbo spin-echo T2-weighted, and contrast-enhanced T1-weighted MR images at 0.2 T

Purpose: To investigate Gd-DTPA kinetics as predictors of histopathological changes following focused ultrasound (FUS) thermal ablation for improved planning and assessment. Materials and Methods:Twenty-nine FUS lesions were created in the thigh muscle of eight rabbits under MRguidance at 1.5 Tesla. Three rabbits were killed at four hours; and 11 lesions were analyzed with histopathology. Temperature-sensitive MRI using proton-resonant frequency-shift was used for time-dependent temperature measurements. Analysis of the uptake kinetics of Gd-DTPA was performed after Gd-DTPA injection, within 20 minutes after heating and again at two hours after heating. The resulting kinetic maps, permeability (K trans ) and leakage space (v e ), were correlated to peak temperatures, T 2 -weighted MR, and histopathology.Results: Images of K trans and v e reveal regions of histopathological change not visible on conventional posttherapy MR. At early times after heating, v e predicts the area of injury more accurately than T 2 (7 Ϯ 2% vs. 25 Ϯ 6% underestimation). A circular region of extensive structural/ vascular disruption is indicated only on K trans maps. The sharp decrease in K trans at the boundary of this region occurs at 47.5 Ϯ 0.5°C, and may be a better estimate of cell death than the conventional method of temperature threshold (55°C for coagulation) used in therapy planning. Conclusion:Our results suggest Gd-DTPA kinetics can predict different histopathological changes following FUS ablation and may be valuable for early prediction.

Section: High-intensity Focused Ultrasound (Fus)supporting

confidence: 84%

Prediction of subtle thermal histopathological change using a novel analysis of Gd‐DTPA kinetics

Cheng

Purcell

Bilbao

et al. 2003

“…In many tissues, including liver and muscle, the characteristic cross-sectional lesion appearance features a hyperintense margin, hereafter called MR zone 2, or M2, enclosing a distinct inner core (zone M1) for both T 2 -and contrastenhanced (CE) T 1 -weighted images, beyond the hyperintense margin is normal tissue (zone M3). A previous study showed that in liver tissue, similar lesion contrast was achievable using either T 2 -or CE T 1 -weighted images (7). A study of skeletal muscle tissue found greater or equal contrast was possible using T 2 -weighted imaging (8).…”

supporting

confidence: 84%

“…A study of skeletal muscle tissue found greater or equal contrast was possible using T 2 -weighted imaging (8). Previous investigations also found that immediately postablation, M1 corresponds to a region of coagulation necrosis, while M2 corresponds to an edematous or hemorrhage surrounding the ablated area (1,3,7,9,10). Typically, clinical ablation is performed such that the M1 boundary exceeds the pathologic tissue boundary by at least a few millimeters as a safety margin.…”

mentioning

confidence: 99%

Radio‐frequency‐induced thermal lesions: Subacute magnetic resonance appearance and histological correlation

Lazebnik

Breen

Fitzmaurice

et al. 2003

Self Cite

Purpose: To investigate the relationship between subacute magnetic resonance (MR) images of radio-frequency (RF) ablation lesions and tissue viability as determined from histological tissue samples. Materials and Methods:We generated lesions (N ϭ 5) in a rabbit thigh model. Four days later, we obtained in vivo T 2 -and contrast-enhanced (CE) T 1 -weighted images and ex vivo histological samples approximately perpendicular to the electrode path. Using three-dimensional registration and warping, we spatially compared manually segmented boundaries apparent on MR images to boundaries separating distinct histological zones determined from hematoxylin and eosin (H&E) and Masson trichrome (MT) stains, as well as birefringence studies.Results: Lesions have a characteristic MR appearance: an outer hyperintense margin (M2) separating background tissue (M3) from an inner core (M1), in both T 2 and CE T 1 images. Histologically, there are two zones of damage: an outer zone of likely nonviable cells (H2) separating background tissue (H3) from an inner core of coagulated nonviable cells (H1). We measured distances between automatically computed correspondence points along histological and MR boundaries. For T 2 and CE T 1 images, respectively, M1 vs. H1 distances were 0.72 Ϯ 0.99 mm (mean Ϯ SD) and 0.10 Ϯ 0.95 mm, while outer M2 vs. H2 boundary distances were 0.26 Ϯ 1.16 mm and 0.05 Ϯ 1.08 mm. The discrepancy between histological and MR boundaries was larger than the variability in segmenting MR images, but probably within registration error. There were no significant differences between T 2 and CE T 1 boundaries. Conclusion:Lesion boundaries apparent in both T 2 -and CE T 1 -weighted MR scans, performed several days postablation, similarly predict the histological response. That is, the lesion core (M1) corresponds to nonviable coagulated cells (H1), while the hyperintense margin (M2) corresponds to likely nonviable cells undergoing necrotic changes (H2).

“…[14]- [16]) can be derived from a trigonometric property (42) and applied to generate wrap-free phase difference images for further processing (10,24,28,38). tory of pixel-by-pixel phase change (24).…”

Section: Discussionmentioning

confidence: 99%

“…[16] can be ignored if and only if the maximum expected phase change between consecutive images is less than Ϯ/2. This includes the superposition of phase associated with a local thermal profile and residual background phase variations.…”

mentioning

confidence: 99%

Variation correction algorithm: Analysis of phase suppression and thermal profile fidelity for proton resonance frequency magnetic resonance thermometry at 0.2 T

Barkauskas¹,

Lewin²,

Duerk³

2003

Self Cite

Purpose: To develop and analyze the performance of the variation correction algorithm (VCA), a phase correction technique that mitigates the contribution of background phase variations by combining accurate alignment of echoes, K-space-based phase correction (as opposed to spatial polynomials), and extraction of alias-free phase difference images. Materials and Methods:A series of echo-shifted gradientrecalled echo (GRE) images was processed with K-space alignment and phase corrected with increasing sizes of M ϫ M masks of central K-space coefficients. The extent of background phase variation suppression due to magnet field drift was assessed. Further, a simulated thermal profile was superimposed on the same data in a related experiment. Residual errors in reconstructed simulated thermal profiles were quantitatively characterized to estimate algorithm performance.Results: Using a 3 ϫ 3 K-space mask, the VCA was able to 1) maintain the typical mean backround error in a 35 ϫ 35 pixel region of interest (ROI) at -0.1°C; and 2) reconstruct, relative to the applied thermal profile, a phase-corrected profile that typically contains a 1.7°C underestimation of peak temperature difference and a mean error along the 60°C line of -0.8°C. Conclusion:The results suggest that thermal profiles can be accurately reconstructed at 0.2 T using the VCA, even in the presence of over 1 ppm spatially and temporally dependent field drift over a 1-hour time frame.