Magnetic resonance imaging of skeletal muscle. Prolongation of T1 and T2 subsequent to denervation

The changes seen in the T1 and T2 relaxation times, water content and size of the extracellular fluid spaces of rat muscle samples following 15 days of denervation were studied by in vitro proton NMR spectrometry (10 MHz). Two different skeletal muscle groups (gastrocnemius and soleus) were studied. Denervation led to longer T1 values: 548 +/- 61 msec vs. 486 +/- 16 msec (P less than .05) for the gastrocnemius and 581 +/- 27 msec vs. 521 +/- 25 msec (P less than .05) for the soleus. Similar increases in T2 were measured. The sizes of the extracellular fluid spaces of denervated muscle were significantly larger despite a minor increase in total water content. Overall, the relaxation times of skeletal muscle correlated better with the size of the extracellular fluid space than with the total water content.     

T1rho relaxation mapping in human osteoarthritis (OA) cartilage: comparison of T1rho with T2

PURPOSE: To quantify the spin-lattice relaxation time in the rotating frame (T1rho) in various clinical grades of human osteoarthritis (OA) cartilage specimens obtained from total knee replacement surgery, and to correlate the T1rho with OA disease progression and compare it with the transverse relaxation time (T2). MATERIALS AND METHODS: Human cartilage specimens were obtained from consenting patients (N = 8) who underwent total replacement of the knee joint at the Pennsylvania Hospital, Philadelphia, PA, USA. T2- and T1rho-weighted images were obtained on a 4.0 Tesla whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA). A 7-cm diameter transmit/receive quadrature birdcage coil tuned to 170 MHz was employed. RESULTS: All of the surgical knee replacement OA cartilage specimens showed elevated relaxation times (T2 and T1rho) compared to healthy cartilage tissue. In various grades of OA specimens, the T1rho relaxation times varied from 62 +/- 5 msec to 100 +/- 8 msec (mean +/- SEM) depending on the degree of cartilage degeneration. However, T2 relaxation times varied only from 32 +/- 2 msec to 45 +/- 4 msec (mean +/- SEM) on the same cartilage specimens. The increase in T2 and T1rho in various clinical grades of OA specimens were approximately 5-50% and 30-120%, respectively, compared to healthy specimens. The degenerative status of the cartilage specimens was also confirmed by histological evaluation. CONCLUSION: Preliminary results from a limited number of knee specimens (N = 8) suggest that T1rho relaxation mapping is a sensitive noninvasive marker for quantitatively predicting and monitoring the status of macromolecules in early OA. Furthermore, T1rho has a higher dynamic range (>100%) for detecting early pathology compared to T2. This higher dynamic range can be exploited to measure even small macromolecular changes with greater accuracy compared to T2. Because of these advantages, T1rho relaxation mapping may be useful for evaluating early OA therapy.     

Calculated T1 and T2 MR images and 31P MR spectra in rabbit thigh V2 carcinoma to monitor the effect of steroid administration

T1 and T2 proton relaxation times in six rabbit thigh V2 carcinomas were obtained from regions of interest on calculated MR images at 2.35 tesla before and after steroid administration. Mean T1 and T2 values of viable tumor tissue decreased after steroid administration, consistent with decreased tissue water content. After steroid withdrawal, T1 and T2 values returned toward baseline. Relaxation times of peritumoral muscle tissue and normal contralateral thigh muscle essentially remained unchanged. In a separate experiment, six rabbit thigh V2 carcinomas were monitored before and after steroids by 31P spectroscopy using a surface coil. No substantial steroid-related changes were recognizable. A fall of the ratio of phosphocreatine to inorganic phosphate and a signal increase from phosphomonoester and phosphodiester compounds were observed during various stages of tumor growth. Analysis of 31P spectra changes and sequential measurements of relaxation times may prove valuable for assessment of tumor growth and therapeutic response in diagnostic oncology.     

MR imaging relaxation times of abdominal and pelvic tissues measured in vivo at 3.0 T: preliminary results

PURPOSE: To measure T1 and T2 relaxation times of normal human abdominal and pelvic tissues and lumbar vertebral bone marrow at 3.0 T. MATERIALS AND METHODS: Relaxation time was measured in six healthy volunteers with an inversion-recovery method and different inversion times and a multiple spin-echo (SE) technique with different echo times to measure T1 and T2, respectively. Six images were acquired during one breath hold with a half-Fourier acquisition single-shot fast SE sequence. Signal intensities in regions of interest were fit to theoretical curves. Measurements were performed at 1.5 and 3.0 T. Relaxation times at 1.5 T were compared with those reported in the literature by using a one-sample t test. Differences in mean relaxation time between 1.5 and 3.0 T were analyzed with a two-sample paired t test. RESULTS: Relaxation times (mean +/- SD) at 3.0 T are reported for kidney cortex (T1, 1,142 msec +/- 154; T2, 76 msec +/- 7), kidney medulla (T1, 1,545 msec +/- 142; T2, 81 msec +/- 8), liver (T1, 809 msec +/- 71; T2, 34 msec +/- 4), spleen (T1, 1,328 msec +/- 31; T2, 61 msec +/- 9), pancreas (T1, 725 msec +/- 71; T2, 43 msec +/- 7), paravertebral muscle (T1, 898 msec +/- 33; T2, 29 msec +/- 4), bone marrow in L4 vertebra (T1, 586 msec +/- 73; T2, 49 msec +/- 4), subcutaneous fat (T1, 382 msec +/- 13; T2, 68 msec +/- 4), prostate (T1, 1,597 msec +/- 42; T2, 74 msec +/- 9), myometrium (T1, 1,514 msec +/- 156; T2, 79 msec +/- 10), endometrium (T1, 1,453 msec +/- 123; T2, 59 msec +/- 1), and cervix (T1, 1,616 msec +/- 61; T2, 83 msec +/- 7). On average, T1 relaxation times were 21% longer (P <.05) for kidney cortex, liver, and spleen and T2 relaxation times were 8% shorter (P <.05) for liver, spleen, and fat at 3.0 T; however, the fractional change in T1 and T2 relaxation times varied greatly with the organ. At 1.5 T, no significant differences (P >.05) in T1 relaxation time between the results of this study and the results of other studies for liver, kidney, spleen, and muscle tissue were found. CONCLUSION: T1 relaxation times are generally higher and T2 relaxation times are generally lower at 3.0 T than at 1.5 T, but the magnitude of change varies greatly in different tissues.     

Spin-lattice relaxation in murine tumors after in vivo treatment with interferon alpha/beta or tumor necrosis factor alpha.

1H NMR spin-lattice relaxation times (T1) were measured in vitro and in vivo in Friend leukemia cell tumors during subcutaneous tumor growth in syngeneic mice and after in vivo administration of either purified murine interferon alpha/beta (IFN) or recombinant tumor necrosis factor alpha (TNF). Untreated tumors exhibited monoexponential T1 relaxation independently of tumor age at least until Day 16 after implantation. Histological examinations showed that under these conditions tumors were highly homogeneous and substantially free of necrotic areas. Peritumoral administrations of either IFN or TNF did not significantly alter the tumor relaxation properties at early stages of inhibition of tumor growth. The longitudinal relaxation decay became instead clearly biexponential at later stages (more than 7 days of IFN treatment or 2 days after TNF administration). While the T1 relaxation behavior could be unequivocally correlated with the presence of necrotic areas in these tumors, it could not be considered as an early marker of the altered growth capability, induced by administration of either IFN or TNF.     

NMR properties of human median nerve at 3 T: Proton density,T1, T2, and magnetization transfer

Purpose

To measure the proton density (PD), the T1 and T2 relaxation time, and magnetization transfer (MT) effects in human median nerve at 3 T and to compare them with the corresponding values in muscle.

Materials and Methods

Measurements of the T1 and T2 relaxation time were performed with an inversion recovery and a Carr‐Purcell‐Meiboom‐Gill (CPMG) imaging sequence, respectively. The MT ratio was measured by acquiring two sets of 3D spoiled gradient‐echo images, with and without a Gaussian saturation pulse.

Results

The median nerve T1 was 1410 ± 70 msec. The T2 decay consisted of two components, with average T2 values of 26 ± 2 msec and 96 ± 3 msec and normalized amplitudes of 78 ± 4% and 22 ± 4%, respectively. The dominant component is likely to reflect myelin water and connective tissue, and the less abundant component originates possibly from intra‐axonal water protons. The value of proton density of MRI‐visible protons in median nerve was 81 ± 3% that of muscle. The MT ratio in median nerve (40.3 ± 2.0%) was smaller than in muscle (45.4 ± 0.5%).

Conclusion

MRI‐relevant properties, such as PD, T1 and T2 relaxation time, and MT ratio were measured in human median nerve at 3 T and were in many respects similar to those of muscle. J. Magn. Reson. Imaging 2009;29:982–986. © 2009 Wiley‐Liss, Inc.     

Multispectral tissue characterization in a RIF-1 tumor model: monitoring the ADC and T2 responses to single-dose radiotherapy. Part II.

A multispectral (MS) approach that combines apparent diffusion coefficient (ADC) and T(2) parameter maps with k-means (KM) clustering was employed to distinguish multiple compartments within viable tumor tissue (V1 and V2) and necrosis (N1 and N2) following single-dose (1000 cGy) radiotherapy in a radiation-induced fibrosarcoma (RIF-1) tumor model. The contributions of cell kill and tumor growth kinetics to the radiotherapy-induced response were investigated. A larger pretreatment V1 volume was correlated with decreased tumor growth delay (TGD) (r = 0.68) and cell kill (r = 0.71). There was no correlation for the pretreatment V2 volume. These results suggest that V1 tissue is well oxygenated and radiosensitive, whereas V2 tissue is hypoxic and therefore radioresistant. The relationship between an early ADC response and vasogenic edema and formation of necrosis was investigated. A trend for increased ADC was observed prior to an increase in the necrotic fraction (NF). Because there were no changes in T(2), these observations suggest that the early increase in ADC is more likely based on a slight reduction in cell density, rather than radiation-induced vasogenic edema. Quantitative assessments of individual tissue regions, tumor growth kinetics, and cell kill should provide a more accurate means of monitoring therapy in preclinical animal models because such assessments can minimize the issue of intertumor variability.     

Lung cancer: differentiation of tumor, necrosis, and atelectasis by means of T1 and T2 values measured in vitro

In vitro measurements of T1 and T2 values were performed in surgical specimens from 15 patients with lung cancer. Correlation between histologic results and measured values revealed that different pathologic tissues can be characterized by means of T1 and T2 values. The transverse magnetization decay curve of the lung tissue was multiexponential, which can be explained by two different relaxation times, fast T2 and slow T2. The signal intensity of pathologic lung tissues at different pulse sequences was simulated on a signal intensity gradient graph based on measured values of T1, fast T2, slow T2, and water content. The results showed that T2-weighted sequences were more valuable in discriminating viable lung cancer from necrotic tumor and collapsed lung lesions.     

Experimental acute pancreatitis: MR relaxation time studies using gadolinium-DTPA

Spin-lattice (T1) and spin-spin (T2) relaxation times of normal and sodium taurocholate-induced pancreatitis (38 rats) were determined in vitro using a 10.7-MHz magnetic resonance (MR) spectrometer. The increase in pancreatic T1 time in acute hemorrhagic pancreatitis correlated well with the elevated water content of the organ. Gadolinium-DTPA did not affect significantly the relaxation times of normal pancreas in vitro during 1 t 20 min postinjection, but it decreased the elevated T1 times of inflamed pancreas almost to baseline values. MR imaging studies of rat pancreas in vivo (8 rats, 0.35-T resistive magnet) indicated that the swollen pancreas and associated edema were depicted using a T2-weighted SE sequence. Fifteen minutes postinjection of gadolinium-DTPA a homogeneous enhancement of inflamed pancreas was detected. The differentiation of pancreatic necrotic foci from surrounding viable tissue and edema could not be detected on Gd-DTPA-enhanced MR images after 15 min postinjection although microscopical workup indicated these different tissue constituents in the pancreas.     

Sodium T2* relaxation times in human heart muscle

PURPOSE: To determine sodium transverse relaxation (T2*) characteristics for myocardium, blood and cartilage in humans. METHODS: T2* measurements were performed using a 3D ECG-gated spoiled gradient echo sequence. A 1.5 Tesla clinical scanner and a 23Na heart surface coil were used to examine eight healthy volunteers. In biological tissue, the sodium 23 nucleus exhibits a two-component T2 relaxation due to the spin 3/2 and its quadrupolar nature. The long T2* components of normal myocardium, blood, and cartilage were quantified. For myocardium, the T2* was determined separately for the septum, anterior wall, lateral wall, and posterior wall. RESULTS: The long T2* relaxation time components of 13.3 +/- 4.3 msec (septum 13.9 +/- 3.2 msec, anterior wall 13.8 +/- 5.4 msec, lateral wall 11.4 +/- 4.1 msec, posterior wall 14.1 +/- 3.7 msec), 19.3 +/- 3.3 msec, and 10.2 +/- 1.6 msec, were significantly different for myocardium, blood, and cartilage, respectively (P < 0.00001, Friedman's ANOVA). CONCLUSION: Measurement of 23Na T2* relaxation times is feasible for different regions of the human heart muscle, which might be useful for the evaluation of cardiac pathologies.     

Multispectral quantification of tissue types in a RIF-1 tumor model with histological validation. Part I.

Accurate assessments of therapeutic efficacy are confounded by intra- and intertumor heterogeneity. To address this issue we employed multispectral (MS) analysis using the apparent diffusion coefficient (ADC), T(2), proton density (M(0)), and k-means (KM) clustering algorithm to identify multiple compartments within both viable and necrotic tissue in a radiation-induced fibrosarcoma (RIF-1) tumor model receiving single-dose (1000 cGy) radiotherapy. Optimization of the KM method was achieved through histological validation by hematoxylin-eosin (H& and E) staining and hypoxia-inducible factor-1alpha (HIF-1alpha) immunohistochemistry. The optimum KM method was determined to be a two-feature (ADC, T(2)) and four-cluster (two clusters each of viable tissue and necrosis) segmentation. KM volume estimates for both viable (r = 0.94, P < 0.01) and necrotic (r = 0.69, P = 0.07) tissue were highly correlated with their H&E counterparts. HIF-1alpha immunohistochemistry showed that the intensity of HIF-1alpha expression tended to be concentrated in perinecrotic regions, supporting the subdivision of the viable tissue into well-oxygenated and hypoxic regions. Since both necrosis and hypoxia have been implicated in poor treatment response and reduced patient survival, the ability to quantify the degree of necrosis and the severity of hypoxia with this method may aid in the planning and modification of treatment regimens.     

MR imaging of adrenal masses smaller than 5 cm. Characterization with T2 relaxation time at 1.5 T]

The T2 relaxation times of 28 adrenal masses smaller than 5 cm obtained using a 1.5 Tesla MR imaging system were analysed to evaluate the ability of this parameter to characterize the tissue masses. The adrenal masses included 13 nonhyperfunctioning adenomas, five hyperfunctioning adenomas, five metastatic tumors, two pheochromocytomas, one nodular hyperplasia, one ganglioneuroma, and one cyst. The mean T2 value of nonhyperfunctioning adenomas was almost the same as that of hyperfunctioning adenomas. A significant difference was found in T2 (p less than 0.01) between nonhyperfunctioning adenoma (50 msec +/- 7 msec; mean +/- S.D.) and metastatic tumor (63 msec +/- 11 msec), whereas there was no significant difference in mass size between them. The two pheochromocytomas and the ganglioneuroma, which were derived from adrenal medulla, had relatively long T2 of over 70 msec. The T2 values of nodular hyperplasia and adrenal cyst were 58 msec and 123 msec, respectively. Although the T2 values of metastatic tumors tended to be longer than those of nonhyperfunctioning adenomas, differentiation between them with a T2 of 60 msec was not necessarily possible, especially in smaller masses. The T2 values of two metastatic tumors of less than 2 cm indicated 50 msec levels. There seemed to be a correlation between mass size and T2 in metastatic tumors. In adenomas, however, no significant correlation was demonstrated. We conclude that the characterization of small adrenal masses by T2 at 1.5 Tesla is unsatisfactory in differentiating metastatic tumors from nonhyperfunctioning adenomas.     

Combined T1-T2 mapping of human femoro-tibial cartilage with turbo-mixed imaging at 1.5T

PURPOSE: To evaluate the influence of Gd-DTPA on cartilage T2 mapping using turbo-mixed (tMIX) imaging, and to show the possible usefulness of the tMIX technique for simultaneously acquiring T1 and T2 information in cartilage. MATERIALS AND METHODS: Twenty volunteers underwent MRI of the knee using the tMIX sequence before and after gadolinium administration. T1 and T2 maps were calculated. The mean T1 was determined on the pre- and postcontrast T1 maps. T2 relaxation values before and after gadolinium administration were statistically analyzed. RESULTS: The obtained relaxation values are in correspondence with previously published data. The mean T1 before gadolinium administration was 449 msec +/- 34.2 msec (SD), and after gadolinium administration it was 357 msec +/- 55.8 msec (SD). The postcontrast T1 relaxation range was 221.5-572.8 msec. The mean T2 of the precontrast T2 maps was 34.2 msec +/- 3.1 msec (SD), and the mean T2 of the postcontrast T2 maps was 32.5 msec +/- 3.1 msec (SD). These are statistically significant different values. A correction for the postcontrast T2 values, using a back-calculation algorithm, yielded a 98% correlation with the precontrast T2 values. CONCLUSION: The absolute difference of pre- and postcontrast T2 is very small and is ruled out using the back-calculation algorithm. Combined T1-T2 tMIX cartilage mapping is a valuable alternative for separate T1 and T2 cartilage mapping.     

In vitro proton T1 and T2 studies on rat liver: analysis of multiexponential relaxation processes

At 37 degrees C and 20 MHz, the T1 and T2 proton relaxation processes in intact rat liver tissue are multiexponential functions which in the majority of cases were decomposed into a major (alpha* approximately 90%, T1* = 374 ms, T2* = 58 ms) and a minor (alpha** approximately 10%, T1** = 130 ms, T2* = 181 ms) component. Both, T1 and T2, are temperature-dependent with a temperature shift of delta T1 = 1.5 ms/degrees C and delta T2 = 0.5 ms/degrees C, respectively. Storage of liver tissue at 4 degrees C and 37 degrees C led to remarkable changes of the T1 and T2 values. For T2 these changes occurred after a shorter storage time than for T1, but they are more pronounced for T1. To avoid such influences the relaxation measurements were performed within one hour after excision of the tissue. Even at 4 degrees C, long-term storage (greater than 3 h) must be avoided. A method for the quantitative determination of the fat content in liver based on multiexponential analysis of the T1 relaxation process was evaluated employing mixtures of triolein with liver homogenate. Triolein is a two-component system with T1* = 144 ms (alpha* = 62%) and T1** = 355 ms (alpha** = 38%). Finally, liver-specific protocol conditions were defined for in vitro relaxation studies.     

MR imaging of the thyroid

The thyroid gland was evaluated with MR imaging in six normal subjects and 32 patients with thyroid disease. The purpose was to evaluate signal characteristics of normal and diseased thyroid tissue; determine the contrast between normal and diseased tissue on T1- and T2-weighted images; compare relaxation times of normal thyroid, adenomas, and carcinoma; and assess the capability of MR for showing the extent of large thyroid masses. Adenomas and carcinomas were frequently isointense with normal thyroid tissue on T1-weighted images but had markedly higher intensity on T2-weighted images. The mean T1 (1202 +/- 717 msec) and T2 (118 +/- 48 msec) relaxation times of adenomas were markedly longer than the T1 (721 +/- 97 msec) and T2 (59 +/- 10 msec) times of normal thyroid tissue. Likewise, the T1 and T2 values of carcinomas were markedly prolonged compared with normal thyroid but the values overlapped with those of the adenomas. Sagittal and coronal images effectively depicted the extent of large goiters, adenomas, and carcinomas and indicated extension below the cervicothoracic junction. The marked prolongation of relaxation times associated with thyroid disease causes excellent contrast of lesions with normal thyroid and surrounding structures. The large field of view possible with coronal and sagittal images is useful for assessing extensive thyroid masses. These attributes indicate the potential clinical utility of MR for evaluating thyroid disease.     

Tissue relaxation time: in vivo field dependence

Relaxation times (T1 and T2) were measured in vivo in mongrel dogs at fields of 0.3, 0.5, 1.0, 1.35, and 1.5 tesla (T). T1 was measured using nine values of inversion time ranging from 10 to 1,280 msec. T2 was measured with a four-point multiple spin-echo sequence. Relaxation times were calculated for muscle, kidney cortex, spleen, and adipose tissue. T2 is independent of field. A linear fit to the field dependence of T1 yields slopes of 400-500 msec/T for tissues in which the primary source of protons is water. The lower slope of adipose (approximately 150 msec/T) reflects the different mechanism of spin-lattice relaxation of the -CH2 protons.     

Differentiation of hepatocellular carcinoma and hepatic metastasis from cysts and hemangiomas with calculated T2 relaxation times and the T1/T2 relaxation times ratio

PURPOSE: To determine the diagnostic capability of the T1 and T2 relaxation times and the T1/T2 relaxation times ratio generated with the mixed turbo spin echo (mixed-TSE) pulse sequence, in order to discriminate between hepatocellular carcinoma (HCC)/metastases and hemangiomas/cysts. MATERIALS AND METHODS: A retrospective review of 36 MR examinations implementing the mixed-TSE pulse sequence demonstrated 70 focal hepatic lesions. Quantitative MR algorithms were used to generate T1 and T2 relaxation times, and the T1/T2 relaxation times ratio for each lesion. A two-sample t-test compared mean T1 and T2 relaxation times, and the T1/T2 relaxation times ratio, by lesion type: carcinoma/metastases and hemangiomas/cysts. Sensitivity and specificity for discriminating carcinoma/metastases from hemangiomas/cysts with T2 relaxation time thresholds of 112 and 125 msec, as well as a ratio of T1/T2 relaxation times of 5.8, were calculated. RESULTS: Using a T2 relaxation time threshold of 112 msec, 92% sensitivity and 100% specificity discriminating cysts/hemangiomas from HCC/liver metastasis was demonstrated. With a threshold of 125 msec, 96% sensitivity and 98% specificity was demonstrated. There was no correlation between calculated T1 relaxation times and type of lesion. Using a T1/T2 relaxation times ratio of 5.8, 100% sensitivity and specificity were demonstrated. CONCLUSION: Although there is high sensitivity and specificity associated with the use of T2 relaxation times alone to discriminate carcinoma/metastases from hemangiomas/cysts, using the T1/T2 relaxation times ratio threshold of 5.8 allowed proper classification of all lesions.     

Theoretical considerations for optimizing intensity differences between primary musculoskeletal tumors and normal tissue with spin-echo magnetic resonance imaging

In the radiographic assessment of primary musculoskeletal tumors, it is important for therapy planning to accurately define the extent of a tumor. Using a double spin-echo pulse sequence, the T1 and T2 relaxation times and relative hydrogen densities of several neoplastic tissues and of several normal tissues in four patients were measured. Neoplasms measured included one fibrosarcoma, two osteosarcomas, and one giant cell tumor. Normal tissues measured included normal muscle, fat, and bone marrow. Using a mathematical model of the double spin-echo pulse sequence, the intensity difference between each tumor and each normal tissue for multiple values of TR and TE was calculated. These calculated intensity differences were then used to plot isodifference contour curves for each tissue pair. These plots enabled us to pick combinations of TR and TE that optimized the signal difference between tumor and normal tissue. When comparing tumor with predominantly fatty tissue such as marrow or subcutaneous fat, optimal signal difference in our imager occurred at a TR of 600 to 800 msec and a very short TE. When comparing tumor with muscle, optimal signal difference occurred with very long TR times, and TE times ranging from 30 to 90 msec. These preliminary results suggest that an optimal scanning protocol for primary musculoskeletal tumors should contain at least two different pulse sequences with widely separated TR values (500 and 2000 msec in our instrument), and short to intermediate values of TE (28 and 56 msec in our instrument). It is believed that analysis of isodifference contour plots is a useful method for optimizing intensity differences between any two tissue types.     

Rectal carcinoma: high-spatial-resolution MR imaging and T2 quantification in rectal cancer specimens

PURPOSE: To prospectively compare high-spatial-resolution T1-weighted, T2-weighted, and intermediate-weighted spectral fat-saturated magnetic resonance (MR) imaging for the differentiation of tumor from fibrosis and for delineation of rectal wall layers in rectal cancer specimens. MATERIALS AND METHODS: The local ethics committee approved the protocol, and written informed consent was obtained from each patient. Thin-section high-spatial-resolution MR imaging was performed in specimens obtained from 23 patients (16 men, seven women; median age, 64 years; age range, 39-84 years) immediately after resection. Seven patients underwent neoadjuvant treatment. T1-weighted spin-echo, T2-weighted fast spin-echo, and intermediate-weighted spectral fat-saturated MR images were obtained in the transverse plane. Differences in signal intensity between tumor and fibrosis and between tumor and rectal wall layers were evaluated by using visual scoring and measurements of T2 relaxation time. Statistical differences were evaluated by using the Wilcoxon signed rank test and a mixed-model regression analysis. All images were compared with whole-mount histopathologic slices (n = 86). RESULTS: T2-weighted MR images provided the best differentiation between tumor and fibrosis (P < .001). Mean visual signal intensity scores were -1.8 for T2-weighted MR images, -1.4 for intermediate-weighted spectral fat-saturated MR images, and -0.2 for T1-weighted MR images. T2 relaxation times were 97 msec +/- 4.6 for tumor and 70 msec +/- 3.8 for fibrosis (P < .001). Substantial overlap was noted between the tumor and the circular layer of the muscularis propria (97 msec +/- 2.1), and less overlap was noted between the tumor and the longitudinal layer of the muscularis propria (88 msec +/- 1.6). CONCLUSION: T2-weighted MR imaging provides superior delineation of rectal wall layers and better differentiation of tumor from fibrosis in rectal cancer specimens compared with T1-weighted MR imaging and intermediate-weighted spectral fat-saturated MR imaging by using thin-section high-spatial-resolution sequences.     

Selective enhancement of experimental rat brain tumors with Gd-TPPS

The synthetic metalloporphyrin gadolinium (III)-tetraphenylporphine sulfonate (TPPS) was successfully used as a contrast agent for in vivo magnetic resonance (MR) imaging of rat brain glioma. After injection of Gd-TPPS, the signal intensity of experimental rat brain glioma distinctly increased on T1-weighted MR images, an effect similar to that produced by the clinically applied MR imaging contrast agent gadolinium diethylenetriaminepentaacetic acid (DTPA). In contrast to other contrast agents studied (Gd-DTPA, manganese [III]-TPPS), Gd-TPPS produced hypointensity in glioma on T2-weighted images. The tumor-selective accumulation of paramagnetic Gd-TPPS in glioma shortened T1 by 53%, from 1,315 msec ± 199 to 628 msec ± 106, and T2 by 34%, from 86 msec ± 4 to 57 msec ± 5 (2 days after injection of 0.25 mmol/kg Gd-TPPS). The relaxation times of normal cortex, striaturn, corpus callosum, and temporal muscle were not significantly affected. As a result, gliomas appeared hyperintense on T1-weighted images and hypointense on T2-weighted images. Owing to the strong effect of Gd-TPPS on the T2 of glioma, normal brain tissue, tumor, and peritumorous edema could be distinguished on T2-weighted images alone.