In Vitro Imaging of MRI and Ultrasound for Gastric Carcinoma

PURPOSE: To evaluate and compare the diagnostic accuracy of MRI and ultrasound(US) for estimation of invasion depth of gastric carcinoma by correlation with histopathologic findings in vitro and to find out the best MR pulse sequence for detection and accurate delineation of tumor. MATERIALS AND METHODS: Resected specimen of total or subtotal gastrectomy from 53 patients with gastric carcinoma were done of imaging studies of MRI and US. And US was examined by using high frequency linear transducer for tumor invasion depth by a radiologist. In each case, both imaging findings of MRI and US were evaluated independently for tumor detection and invasion depth by consensus of two radiologists and were compared the diagnostic accuracy between two imaging modalities according to the histopathologic findings. MR imaging with five MR pulse sequences, spin echo T1 and in- and out-ofphase gradient echo T1 weighted images, FSE and SSFSE T2 weighted images, were performed. Five MR pulse sequences were evaluated and compared on the point of detection and accurate distinction of tumor from surrounding normal tissue. RESULTS: In EGC, diagnostic accuracy of US(77%) was superior than that of MRI(59%) but no statistically significant difference was noted between two imaging modalities(p=0.096). In AGC, both imaging modalities of MRIand US showed relatively high diagnostic accuracy as 97% and 84% respectively. Diagnostic accuracy of MRI was statistically better than that of US at the significant level(p<0.001). The best MR pulse sequence among five in each specimen was FSE T2WI(75.5%, 40/53) in both EGC and AGC. In AGC, FSE T2WI showed excellent imaging quality by showing very high ratio (93.5%, 29/31) of accurate delineation of tumor. CONCLUSION: MRI and US show relatively high diagnostic accuracy in the evaluation of tumor invasion depth of resected specimen in AGC. The most excellent pulse sequence of MRI for the evaluation of tumor invasion depth is FSE T2WI on the point of detection and accurate delineation of tumor in both EGC and AGC.

In Vitro of MR Imaging of the Resected Normal Gastric Wall: Radiologic-Histologic Correlation

PURPOSE: To evaluate normal human gastric wall layers in vitro using magnetic resonance*(MR) imaging, to correlate the results with the histologic findings, and to determine the optimal technique for evaluation of the gastric wall. MATERIALS AND METHODS: Forty-one normal resected gastric specimens obtained from 25 patients were dissected and placed in a polyethylene tube filled with normal saline. MR imaging with four MR sequences, T1-weighted FLASH*(T1FLASH), fat-saturated T1-weighted FLASH, T2-weighted TSE*(T2TSE), and True-FISP, was performed. The number of gastric wall layers and signal intensity of each layer were determined, and after correlating MR images with the histologic findings, the conspicuity of each layer*(mucosa, submucosa, and muscle), the distinction between each layer, and overall image quality were assessed. RESULTS: The gastric wall was shown by TIFLASH to have two (n=6, 14-6%), three (n=31, 75.6%) and four layers (n=4, 9.8%); by fat-saturated TIFLASH to have two (n=6, 14.6%) and three (n=35, 85.4%) ; by T2TSE to have three (n=24, 58.5%), four (n=11, 26.8%), and five (n=6, 14.6%); and by True-FISP to have one (n=2, 4.9%), two (n=8, 19.5%), three (n=23, 56%), four (n=4, 9.8%), and five (n=4, 9.8%) . The signal intensity of each layer at T1FLASH and fat-saturated T1FLASH was high-intermediate from the lumen in two-layer cases, high-low-high/intermediate in three-layer cases, and high-low-high-intermediate in four-layer cases. The signal intensity of each layer at T2TSE was intermediate/high-low-intermediate in three-layer cases, intermediate low-high-intermediate/low in four-layer cases, and low-high-low-high-low in five-layer cases. Three-layered gastric wall corresponded mostly to mucosa, submucosa, and muscle from the inner to outer layers, respectively. T1FLASH, fat-saturated T1FLASH, and T2TSE were superior to True-FISP in evaluating the gastric wall. T1FLASH and fat-saturated T1FLASH were the best sequences for demonstrating mucosa (p<0.05), and T2TSE was the best for submucosa and the distinction between this and muscle (p<0.05). Both T1FLASH and T2TSE provided the best overall image quality (p<0.05). CONCLUSION: In-vitro MR imaging is an excellent technique for the evaluation of layers of normal gastric wall. T2TSE is the sequence which best demonstrates the conspicuity of submucosa, the distinction between submucosa and muscle, and overall image quality.

Osteosarcoma: Correlation of T1 Map and Histology Map

PURPOSE: To determine whether T1 mapping shows regional differences between viable and necrotic regions of osteosarcomas after anticancer chemotherapy and to assess whether this mapping is able to express the characteristics of various intramural tissue components. MATERIALS AND METHODS: Eleven of 20 osteosarcomas were included in this study, while the remaining nine were excluded because the tumor site was inappropriate for comparison of T1 map and tumor macrosection. All patients underwent MR imaging for the purpose of T1 mapping, followed by pre-operative chemotherapy and subsequentl limb-salvage surgery. Spin echo pulse sequencing was used with varying TR (100, 200, 400, 800, 1600, and 2400 msec) and a constant TE of 20 msec. Using a C-language software program, T1 relaxation time was calculated on a pixel-by-pixel basis and then a T1 map was generated by using a post-processing program, NIH Image. We attempted correlation of the T1 map and histologic findings, particularly in regions of interest(ROI) if certain areas were different from other regions on either the T1 or histologic map. Value was expressed as an average of the ratio of T1 of ROI and T1 of fat tissue, and this was used as an internal reference for normalization of the measurement. RESULTS: Tumor necrosis was 100%(Grade IV) in six specimens, and over 90 % (Grade III) in five. Viable tumor cells were found mostly in regions with chondroid matrix and seldom in regions with osteoid matrix. Regardless of cell viability, values ranged from 0.9 to 9.87(mean, 4.02) in tumor necrotic area with osteoid matrices, and from 3.04 to 3.9(mean, 3.55) in areas with chondroid matrices. Other regions with fibrous tissue proliferation, hemorrhage, and fatty necrosis showed values of 2.92-9.83(mean, 7.20), 2.65 -5.96(mean, 3.59), and 1.43 -3.11(mean, 2.68) respectively. The values of various tissues overlapped. No statistically significant difference was found between regions in which tumors were viable and those with tumor necrosis. CONCLUSION: Although we hypothesized that areas of necrotic tumor would show an increased water component(proton number) and would have a longer T1 value than viable tumor tissues, our results were otherwise. Necrotic osteosarcoma tissves showed a wide range of T1 values according to the prevailing tissue components.

Magnetization Transfer Ratio in Head and Neck Lymphadenopathy

PUYPOSE: The purpose of this study was to determine whether the magnetization transfer ratio(MTR) differs between malignant and benign cervical lymphadenopathy. MATERIALS AND METHODS: Magnetization transfer ratios were obtained from 104 lymph nodes of 43 patients. Fifty-five nodes were malignant and 49 were benign. Biopsy or cervical lymph node dissection was performed in 83 nodes, while the remaining 21 were diagnosed clinically or by follow-up imaging studies. Among the 55 malignant nodes, squamous cell carcinomas accounted for 29 cases, lymphomas for 15, undifferentiated carcinomas for four, acute myelogenous leukemia for four, and melanomas for three. The 49 benign nodes comprised 21 cases of reactive hyperplasia, 12 of Kikuchi's disease, nine of acute lymphadenitis, and seven of tuberculous lymphadenitis. All scans were performed using a 1.5T Magnetom Vision(Siemens, Erlangen, Germany) with phased-array or Helmholtz-type neck coil. Scanning was performed with and without magnetization transfer pulse(MT pulse : 11.2 T, 250 Hz band-width, off-set 2.0 KHz) using FLASH 2D sequencing. The region of interest(ROI) for signal intensity(SI) measurements was sampled at the same nodes by keeping the position, shape and size of the ROI constant for the scans before and after the MT pulse was applied. SI measurements were repeated more than three times in each node and the mean value was used to calculate MTR. In this study, however, corrected MTRs(CoMTRs) were used for correction of the effect of background noise produced by magnetic field inhomogeneity. RESULTS: Mean CoMTRs of malignant and benign nodes were 0.33(SD: +/- 0.04) and 0.28(SD: +/- 0.05), respectively. This difference was statistically significant. At CoMTR 0.31, the sensitivity and specificity of malignant nodes were 83% and 75%, respectively. CONCLUSION: A CoMTR of above 0.31 suggests malignant lymphadenopathy. CoMTR is one of the MR criteria which can serve to differentiate between malignant and benign lymphadenopathy.

Osteosarcoma after Preoperative Chemotherapy: Tissue Characterization with Specimen MR and the Role of Enhanced MR Imaging

PURPOSE: To evaluate the role of enhanced MR imaging in monitoring tumor response to preoperativechemotherapy for osteosarcomas. MATERIALS AND METHODS: Fo r t y - s even patients (30 males and 17 females, witha mean age 17 years ; range 8 -44 years) with osteosarcomas were included in this study. We obtained spin echoT1-, T2-, and enhanced T1-weighted images before and after pre-operative chemotherapy and in all patientscorrelated changes in MR parameters with histopathologic response. We also obtained 19 specimen MR images,correlating these with histopathologic results in order to estimate tissue specific signals. Patients with morethan 10% viable tumor in the resected specimen were considered poor respon-ders(n=26), while those with 10% orless viable tumor were considered good respon-ders(n=21). RESULTS: Four distinct patterns of signal intensitycorresponded, respectively to dead bone and dense fibrosis (low on T1- and T2-weighted images), viable tumor cells(in-termediate on T1- and high on T2-weighted images), necrosis (low on T1- and high on T 2 - weighted images),and hemorrhage (high on T1- and T2-weighted images), but a wide range of overlap was noted. In all four groups,viable tumor cells remained. Increased tumor vo l u m e, stable or increased edema and enhancement were goodpre-dictors of poor response (predictive values of 83%, 77%, and 89%, respectively). Decreased enhancement was theonly reliable predictor of good response (predictive value, 73%). Changes in tumor margin, homogeneity, signalintensity, and joint effu-sion did not correlate with histopathologic response. CONCLUSION: Signal intensities donot reflect histologic nature. Enhanced MR imaging is a useful predictor of tumor response to preoperativechemotherapy.

MR Imaging Findings of Chondroblastic Osteosarcoma

PURPOSE: To evaluate the MR imaging findings of chondroblastic osteosarcoma. MATERIALS AND METHODS: Weincluded 11patients (8 men, 3 women, mean age of 19 years) with pathologically proven chondroblastic osteosarcomaand, as a control group, 20 patients with conventional osteosarcoma. We obtained pre- and post-enhanced MR imagesof all patients and retrospectively reviewed the signal intensity and enhancement pattern of tumors. MR imageswere correlated with histopathology. RESULT: In chondroblastic osteosarcomas, the major portion (< 75%) of thetumor showed low signal intensity on T1-weighted images and homogeneous high signal intensity on T2-weightedimages, but did not show enhancement. The margin of the area showed a lobular pattern. Enhanced nodules (n=11) andstrands (n=8) were seen in the nonenhanced portion. Histopathologically, the nonenhanced portion, nodules, andstrands revealed a chondroid matrix, hypercellular area, and fibrovascular septa, respectively. Conventionalosteosarcomas showed heterogeneous enhancement ; six showed a focal (<25%) nonenhanced area representing necrosis. CONCLUSION: Chondroblastic osteosarcoma showed characteristic MR imaging findings.

Sequential Changes of Fresh and Fixed Specimen on MRI: Optimal Time Interval and Fixatives for Good Correlation with in Vivo State

PURPOSE: With the development of MR Imaging techniques, MRI and MR spectroseopy can be used to evaluatespecimens both in vivo and in vitro. For extracted tissue specimens we wished to obtain MR images which correlatedwell with images obtained in vive; the purpose of this study was to determine which fixatives and time intervalbest facilitated this objective. MATERIALS AND METHODS: After in vivo MR imaging, sample tissues of liver, renalcortex and renal medulla were obtained from ten healthy rabbits. Each tissue sample was placed in 75% ethanol, 10%formalin, and 0.9% normal saline and MR scans of each sample were performed at 30 minutes, 11/2, 3, 6, and 12hours after resection. Signal intensities of the images were measured and their sequential changes were evaluated. RESULTS: On T1WI, signal intensities of both tissue specimens fixed in formalin and ethanol and untreatedspecimens increased significantly during the first 30 minutes. The increased signal intensity then seen for 12hours was greater than on T2WI. On T2WI, signal ntensities of tissue specimens fixed in formalin and ethanol anduntreated specimens showed no significant changes within the first 30 minutes; after that, they showed less signalintensity change for 12 hours than on T1WI. CONCLUSION: To obtain MR images with the same signal intensities as invivo tissue, MRI of tissue specimens in the untreated state should be performed as soon as possible afterresection. On T2WI, signal intensities of tissue specimens were more similar to in vivo tissue than on T1WI.

MR Imaging Findings of Synovial Sarcoma: Emphasis on Signal

PURPOSE: To determine the MR imaging findings of synovial sarcoma, with emphasis on the signal characteristicsof pathologically correlated T2-weighted images. MATERIALS AND METHODS: MR images of 14 cases ofpathologically-proven synovial sarcomas were retrospectively reviewed and correlated with the histopathologicfindings. We analyzed the signal intensity of T1- and T2-weighted images and the incidence of triple signalintensity, and evaluated the frequency of fluid-fluid levels, internal fibrous septa, calcification, the invasionof bone or neurovascular bundles and the involvement of joint capsules, as well as the size, location and marginof the tumors and pattern of contrast enhancement. RESULTS: Necrosis, cystic change or hemorrhage was suggested in11 cases, ten of which showed triple signal intensity, and in all cases, was pathologically confirmed. Fluid-fluidlevels were found in three cases and internal septa in ten. In four cases, maximum diameter was less than 5cm, andin nine, was greater than this. No mass was detected in one case. The tumor was located in the low extremity(n=9),pelvic girdle and hip joint area(n=2), scapular(n=1), shoulder joint area(n=1), and scalp(n=1). Eleven casesshowed a relatively well-defined margin and nine showed lobulation. Except in the area of necrosis and cysticchange, the pattern of contrast enhancement was diffuse and inhomogenous. Bony invasion was detected in two cases,neurovascular encasement in four, calcification in four, and joint capsule invasion in four. CONCLUSION: OnT2-weighted images, synovial sarcoma frequently showed triple signal intensity and internal septa with fluid-fluidlevels ; this was induced by cystic changes due to necrosis and hemorrhage.

MR Imaging of Focal Hepatic Masses: Comparison between Half-Fourier Acquisition Single-shot TSE(HASTE) andSingle-shot Echo Planar Imaging

PURPOSE: We undertook this study to evaluate breath-hold Half-Fourier Acquisition Single-shot TSE(HASTE) andsingle-shot echo planar MR imaging for the detection of focal hepatic masses. MATERIALS AND METHODS: Using a 1.5Tsuperconductive system, HASTE, vascular dephasing inversion recovery spin echo EP(VDIR-SE-EP), inversion recoveryspin echo EP(IR-SE-EP), and free induction decay EP(FID-EP) were performed in 31 patients with 34 focal livermasses. Images were compared on the basis of detection sensitivity of focal hepatic masses, liver signal-to-noiseratio(S/N), lesion-to-liver contrast-to-noise ratio(C/N), and image quality. Images analysis was performed by tworadiologists, who reached a consensus. RESULT: The detection sensitivity of focal hepatic masses with HASTE was94.1%, with VDIR-SE-EP and IR-SE-EP, this was 91.2%, and with FID-EP, the figure was 88.2%. Liver S/Ns werehighest on HASTE images, which were significantly better(p<.05) than the three types of EP image. Overalllesion-to-liver C/Ns were highest on VDIR-SE-EP and IR-SE-EP(p<.05). Lesion-to-liver C/Ns were highest onVDIR-SE-EP and IR-SE-EP for solid lesions, but for non-solid lesions, were highest on HASTE (p<.05). Compared withHASTE images, EP images were poor. CONCLUSION: For the detection of focal hepatic masses, the sensitivity ofVDIR-SE-EP and IR-SE-EP was similar to that of HASTE. When using the former, acquisition time was substantiallyreduced but image quality was poor.

Role of EPI in Diagnosing Cavernous Hemangioma & Small HCC: Comparision with Fast T2-Weighted MR Imaging

PURPOSE: To compare single-shot echo-planar MR imaging(EPI) with breath-hold fast T2-weighted imaging(HASTEor Turbo spin-echo T2WI) for evaluation of the role of EPI in distinguishing small hepatocellular carcinoma fromcavernous hemangioma. MATERIALS AND METHODS: We retrospectively evaluated MR images of 35 patients (21 cases ofsmall HCC and 14 cases of cavernous hemangioma). EPI and breath-hold fast T2WI images were obtained and comparedon the basis of lesion detection sensitivity, lesion-to-liver signal intensity ratio(SIR), contrast ratio(CT), andlesion-to-liver contrast to noise ratio(CNR). RESULTS: For the detection of small HCC, the sensitivity of EPI andbreath-hold fast T2WI were equal in 14 of 21 cases(71.4%). The detection sensitivity of cavernous hemangioma withEPI and breath-hold fast T2WI was 100%(14/14). Mean SIR on breath-hold fast T2WI was 2.02+/-0.45 for small HCC and3.65+/-0.97 for cavernous hemangioma; on EPI, the corresponding figures wer 2.91+/-0.57 and 6.98+/-1.37. Mean CR onbreath-hold fast T2WI was 1.16+/-0.58 for small HCC and 2.65+/-0.57 for cavernous hemangioma; On EPI, the figuresobtained were 2.27+/-0.52 and 6.26+/-2.19, respectively. Mean CNR on breath-hold fast T2WI was 14.24+/- 4.098 forsmall HCC and 50.28+/-10.96 for cavernous hemangioma, while on EPI, the corresponding figures were 13.84+/-3.02 and45.44+/-11.21. CONCLUSION: In detecting focal hepatic mass, the sensitivity of EPI and breath-hold fast T2WI arecomparable; for the diagnosis of small HCC and cavernous hemangioma, EPI can provide additional information.

Musculoskeletal Adipose tumors of the extremities: Benign vs Malignancy in MR Imaging

PURPOSE: The purpose of this study was to evaluate the MR findings of benign and malignant musculoskeletal adipose tumors and to determine the points of difference between these two types. MATERIALS AND METHODS: This study involved 41 histopathologically proven cases; 26 were benign lipoma and 15 were liposarcoma. T1- and T2-weighted images were obtained in all cases and enhancement study was performed in 15 case of benign lipoma and14 of liposarcoma. To determine MR findings and possible differences between the two groups, we retrospectively analyzed size, location, margin, degree of signal intensity, homogeneity, enhancement pattern and internal septa, as seen on MR images. RESULTS: On both T1- and T2-weighted images, all lipomas showed a signal intensity similar to that of subcutaneous fat. Twenty-one lipomas had thin and regular internal septa and three showed focal enhancement. On T1-weighted images, 13 of 15 liposarcomas showed linear strands or patchy or diffuse areas with high signal intensity, representing a fatty component. Ten liposarcomas showed inhomogeneous signal intensity and the other five, homogeneous intensity. Irregular and thick septa were seen in nine liposarcomas, and in 12 cases, nodular diffuse enhancement was documented. CONCLUSION: Homogeneity of signal intensity, enhancing pattern and internal septa might be useful MR findings for the differential diagnosis of benign lipoma and liposarcoma.

A Study on MR Signal Intensity of Calcifications According to Calcium Concentration and Compound

PURPOSE: The signal of intracranial calcification on magnetic resonance (MR) imaging has been known to bevariable. The purpose of this study was to evaluate the MR signal of calcifications according to calciumconcentration and compound. MATERIALS AND METHODS: T1-weighted, proton density and T2-weighted images were obtained in phantoms with various conposition of calcium carbonate and calcium phosphate. The signal intensities and T1/T2 relaxation times were measured and analyzed according to calcium concentration and compound. The configurations of calcium particles were evaluated by scanning electron microscopy. RESULTS: The signal intensity of calcium carbonate on T1-weighted images gradually decreased as the concentration increased, while that ofcalcium phosphate showed a biphasic curve with a peak intensity at 0.2 g/ml. The signal intensity of both calcium compounds on T2-weighted images decreased as the concentration increased. The T1 relaxation time of calcium carbonate remained constant with increasing calcium concentration, however, that of calcium phosphate decreased upto 0.2g/ml and then remained constant. The T2 relaxation time of both calcium compounds decreased in a similar fashion with increasing concentration. Calcium phosphate showed larger surface area on scanning electron microscope. CONCLUSION: Calcifications show variable MR signal due to difference of T1 and T2 relaxation times according to calcium concentration and compound. Large surface area of calcium particle might cause shortening of T1 relaxation time leading to high signal on T1-weighted image. Understanding of these findings will help interpretation of MR images more precisely.