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Diffusion-Weighted MR

Posted Apr 30, 2008 Updated Apr 7, 2023
By Byung Jae Youn MD , Jin Wook Chung M.D. , Kyu Ri Son M.D. , Hyo-Cheol Kim MD , Hwan Jun Jae M.D. , Jeong Min Lee MD , In Chan Song PhD , In-One Kim MD , Jae Hyung Park M.D.
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Rationale and Objectives

The study goal was to evaluate the ability of diffusion-weighted imaging (DWI) in assessing the viability of rabbit liver VX-2 tumor after transcatheter arterial chemoembolization (TACE).

Materials and Methods

VX-2 tumors were grown in the livers of 19 rabbits, and chemoembolization was performed. MR imaging was acquired 1 week after TACE. The rabbits were killed for histologic investigation immediately after MR imaging, and the proportion of viable tumor was calculated based on histopathologic examination. Apparent diffusion coefficient (ADC) values were measured in viable and necrotic tumor portion, and were compared using the paired Student’s t test.

Results

Viable tumors were absent (n = 3), less than 5% (n = 6), and 5% or more (n = 10) at pathology examination. On DWI, three tumors with no viable portion were interpreted as having no viable portion, but three of six tumors with a viable portion of less than 5% were considered as having no viable portion. The mean ADC values of necrotic and viable tumor were 1.653 ± 0.126 mm 2 /sec and 0.883 ± 0.407 mm 2 /sec ( b = 1000 sec/mm 2 ), respectively, and the ADC values of necrotic tumors were significantly greater than those in viable tumors ( p < .01).

Conclusion

Although DWI is a useful tool for assessing tumor viability, viable tumor may not be detected on DWI when it is too small.

Hepatocellular carcinoma (HCC) is one of the most frequent malignant tumors ( ). Because of an advanced disease stage and associated liver cirrhosis at its initial presentation, the treatment options are limited and transcatheter arterial chemoembolization (TACE) has been widely performed as a palliative treatment for HCC ( ).

Computed tomography (CT) and conventional magnetic resonance imaging (MRI) do not provide exact information about the extent of tumor cell death and the amount of viable tumor tissue after treatment ( ). Hyperattenuating Lipiodol impairs the assessment of residual tumor enhancement on contrast-enhanced CT ( ). On gadolinium-enhanced MRI, enhancing areas in the lesion are presumed to represent viable tumor, but they could also be due to post-treatment granulation tissue ( ). Diffusion-weighted imaging (DWI) was initially used to evaluate early ischemic brain lesions and its value in this field has been accepted. However, a few studies are available about DWI in evaluating hepatic lesions ( ).

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Materials and methods

Experimental Animals and the Establishments of a VX-2 Tumor Model

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Transcatheter Arterial Chemoembolization

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MRI Technique

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Image and Pathologic Analysis

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Results

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Table 1

Tumors at each image interpretation session and pathologic examination

Tumor Treatment Method Viable Tumor Rate on Pathologic Examination Viable Tumor Rate on Conventional Images Viable Tumor Rate on DWI 1 Lip-dox 17 ≥5 ≥5 2 Lip-dox 0 <5 0 3 Lip-dox 1 ≥5 0 4 Lip-dox 0 <5 0 5 Lip-dox 11 ≥5 ≥5 6 Lip-dox 21 ≥5 ≥5 7 Lip-dox 0 <5 0 8 Lip 15 ≥5 ≥5 9 Lip-eth 60 ≥5 ≥5 10 Lip-eth 1 ≥5 <5 11 Lip 40 ≥5 ≥5 12 Lip-eth 3 <5 0 13 Lip-eth 8 ≥5 ≥5 14 Lip-eth 1 ≥5 <5 15 Lip-eth 1 ≥5 0 16 Lip 25 ≥5 ≥5 17 Lip-dox 5 ≥5 ≥5 18 Lip-dox 3 <5 <5 19 Lip 14 ≥5 ≥5

Lip-dox, Lipiodol-doxorubicin emulsion (1.6 mg doxorubicin/0.4 ml Lipiodol); Lip-eth, Lipiodol-ethylbromopyruvate emulsion (40 mM ethylbromopyruvate/0.4 ml Lipiodol); Lip, Lipiodol 0.4 ml.

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Figure 1, Tumor with no viable portion. (a) Gadolinium-enhanced T1-weighted image reveals peripheral rim enhancement and subtle nodular enhancement ( arrowhead ) raising the suspicion of viable tumor. (b) DWI obtained with b -values of b = 1000 sec/mm 2 shows homogeneous intermediate signal intensity ( arrowheads ) reflecting the totally necrotic nature of the tumor. (c) Macroscopic photograph of pathologic slide shows a large necrotic tumor with no viable portion. A rectangle represents the microscopic field of (d) . (d) Photomicrograph (original magnification, ×40; hematoxylin-eosin stain) shows fibrocollagenous capsule (C) with inflammatory cells between normal liver (L) and necrotic tumor (N).

Figure 2, Tumor with 3% residual viable portion. (a) Gadolinium-enhanced T1-weighted image reveals peripheral rim enhancement ( arrowhead ) and enhancing daughter nodule ( arrow ). (b) DWI obtained with b -values of b = 1000 sec/mm 2 shows homogeneous intermediate signal intensity suggesting total necrosis of the tumor ( arrowheads ) and bright signal intensity of daughter nodule ( arrow ). (c) Macroscopic photograph of pathologic slide shows a large necrotic tumor with small daughter nodule ( arrowheads ). A rectangle represents microscopic field of (d) . (d) Photomicrograph (original magnification, ×100; hematoxylin-eosin stain) shows focal viable tumor ( arrow ) between normal liver (L) and necrotic tumor (N).

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Figure 3, Tumor with 3% residual viable portion. (a) Gadolinium-enhanced T1-weighted image reveals peripheral rim enhancement ( arrows ). (b) DWI obtained with b -values of b = 1000 sec/mm 2 shows focal bright signal intensity ( arrow ) indicating viable tumor. (c) Macroscopic photograph of pathologic slide shows a large necrotic tumor with focal viable portion. A rectangle represents microscopic field of (d) . (d) Photomicrograph (original magnification, ×40; hematoxylin-eosin stain) shows focal viable tumor ( arrows ).

Figure 4, Tumor with 17% residual viable portion. (a) Gadolinium-enhanced T1-weighted image reveals peripheral rim enhancement. (b) DWI obtained with b -values of b = 1000 sec/mm 2 . An area of bright signal intensity ( arrowheads ) is identified at periphery of tumor. (c) Macroscopic photograph of pathologic slide shows central necrotic portion (N) and peripheral viable tumor (V). A rectangle represents microscopic field of (d) . (d) Photomicrograph (original magnification, ×40; hematoxylin-eosin stain) shows viable tumor portion (T) between normal liver (L) and necrotic tumor (N).

Table 2

Mean ADC values of viable tumor and necrotic tumor according to b -values

ADC Values Viable Tumor Necrotic Tumor_p_ -Value_b_ = 100 1.269 (0.428) × 10 −3 mm 2 /sec 2.135 (0.756) × 10 −3 mm 2 /sec <.01b = 500 1.047 (0.443) × 10 −3 mm 2 /sec 1.836 (0.489) × 10 −3 mm 2 /sec <.01b = 1000 0.883 (0.407) × 10 −3 mm 2 /sec 1.653 (0.126) × 10 −3 mm 2 /sec <.01

Numbers in parentheses are standard deviation.

ADC, apparent diffusion coefficient.

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Discussion

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Academic Radiology, Volume 15, Issue 5
Journals General Radiology
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