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- Hot Topics in Body MRI All in One: Whole-Body Cancer Imaging
Heinz-Peter Schlemmer, University Hospital Tuebingen, Germany
A malignant tumor is per se potential systemic disease. Early tumor detection,
precise staging and accurate therapy monitoring in individual patients are essential
for achieving best patient outcome in terms of survival and quality of life. Treatment
decisions with either curative or palliative intention consider individual disease
characteristics and identify patients who are candidates for aggressive medical or
surgical interventions particularly. Repeated assessment of the disease progress is
of fundamental importance for controlling the individual treatment success. The
individual proceeding is predominantly based recommendations of multidisciplinary
conferences where diagnostic and therapeutic strategies are carefully balanced
taking all medical and radiological information into account. In this concept, initial
and repeated tumor staging are preconditions for assessing prognosis, planning and
monitoring individually optimized treatment strategies as well as keeping an eye on
the therapy outcome.
Tumor serum markers are important tools for estimating the total tumor load and its
changes during therapy, but they cannot provide information about the localization of
the primary tumor, its extension into surrounding anatomical structures as well as its
lymphatic and hematogeneous spreading. Whole-body imaging is consequently of
fundamental importance for staging. It provides important components of the
decision-making process by identifying both, tumor specific as well as disease or
treatment related abnormalities, e.g. metastatic spreading and chemotherapy
induced pneumonia. Up until a few years ago, only functional nuclear medicine
examination methods enabled whole-body image information, for example,
conventional bone scan with technetium-marked phosphate complexes and, more
recently, positron emission tomography with the radioactive nuclide [18F]-2-Fluoro2desoxy-D-glucose ([18F]-PDG-PET). But over the last 10 years spiral CT has gone
through enormous technical advantages and whole-body imaging became feasible
within one single examination. Whole-body spiral CT evolved rapidly to an
indispensable tool in oncologic radiology enabling high-resolution imaging of the
whole-body within only a couple of seconds. Nevertheless, the limited specificity of
conventional CT morphological criteria for discriminating benign and malignant tissue
remained, e.g. for detecting small lymph node metastases or for discriminating
recurrent tumor from treatment related scar tissue. To solve this fundamental
problem in oncologic radiology the combination of whole-body morphologic and
functional information was urgently required. It was enabled by further advances in
the scanner and computer technology leading to the recent development of PET-CT
hybrid systems. This technology uses full capacity of both imaging methods offering
to acquire metabolic and morphologic data within one single examination and to
superimpose information on color-coded images. Clinical and research applications
are at present tremendously evolving [1-3]. MRI has the distinct advantage to
provide anatomical details with superior soft tissue contrast compared to CT and to
yield additional functional information about e.g. perfusion and metabolism. But the
method was for a long time understood as a dedicated only for evaluating local
disease. Meanwhile, technological progress enabled also high-resolution MRI of the
whole body within one single examination [4].
It is important to note, that the diagnostic accuracy of whole-body MRI strongly
depends on the applied MRI technique. An impairment of spatial and/or contrast
resolution compared to a series of sequentially acquired, conventional partial-body
MRI examinations must be avoided for maintaining the diagnostic accuracy of MRI,
particularly regarding the detection of small metastases, e.g. in the brain or moving
organs like the liver. The use of surface coils and integrated parallel imaging
acquisition technique (iPAT) enables to apply various spin-echo and gradients echo
sequences for achieving equivalent high spatial and contrast resolution of each body
part as compared to conventional MRI examinations of a single body part [4].
Exceptions are small anatomical regions where dedicated coils have necessarily to
be used for high-resolution imaging, e.g. breast, prostate and small joints of hand
and foot. By applying breath-hold or navigator techniques with iPAT, even small
metastases can be detected within a whole-body examination, also in moving organs
like the liver. Tumor lesions can furthermore be characterized by assessing their
characteristic signal behavior on different MR sequences, e.g. diffusion-weighted
(DWI) and spectroscopic MR sequences. The lack of x-ray exposure is favourable
for performing various MR sequences including contrast-enhanced dynamic imaging
studies as well closed follow-up examinations even in young and anticipated healthy
individuals.
Clinical studies comparing whole-body MRI with PET/CT have proven that MRI is
most sensitive for early tumor detection in different organs, like the brain, liver, or
bone marrow [5-8]. Whole-body MRI can accordingly play an important role for
evaluating metastatic disease and for estimating the individual total tumor burden.
Regarding bone metastases, whole-body MRI has been proven to be more sensitive
than conventional bone scintigraphy, X-ray, CT and PET/CT for different tumor
types. Clinical studies with advanced melanoma patients comparing whole-body CT,
MRI and PET/CT have proven the feasibility and clinical potential of high-resolution
whole-body MRI [6, 7]. It has been found that whole-body MRI altered the
therapeutic concept in ca. 25-60% of the examined patients, which was basically
related to the high sensitivity to detect cerebral, hepatic and skeletal metastasis.
Metastases to the lung are frequent sequelae of different tumors and CT is so far the
method of choice for detecting small lung nodules. However, HASTE or 3D GRE
sequences, which can easily be integrated in an wb-MRI protocol, yielded
sensitivities about 90% for 4 to 10 mm nodules and approximately 100% for nodules
larger than 10 mm [9]. Initial results also demonstrate the potential of wb-MRI to
detect lung metastases. One major drawback of MRI remains the limited accuracy
for early detection of lymph node metastases. Novel contrast media containing
lymphotropic paramagnetic nanoparticles (USPIO) may help to increase the
specificity [10].
To screen for multifocal tumor growth or distant tumor spreading whole-body can on
principle be applied for all kind of malignant tumors. In order to minimize the total
examination time, however, a whole-body MRI examination protocol should focus on
the specific pathophysiology of the tumor as different tumors types are characterized
by different patterns of local growth and systemic spreading. Regarding
haematogenous spreading, for example, prostate cancer preferentially develops
osteoblastic bone metastases, whereas colorectal carcinomas tend to initially spread
into the liver or bronchial carcinoma into the brain. Accordingly, disease specific
examination protocols have been implemented in our institution, which are based on
a modular concept combing different organ specific examination protocols according
to the specific tumor entity and individual risk factors [11]. The examination protocols
are leant against oncologic guidelines and extended according to the individual
clinical situation.
Whole-body imaging significantly increases the number of acquired images per
patient. One examination comprises up to 1000 images, which all have carefully to
be reviewed for the presence or absence of suspicious mass lesions consuming a
notable amount of time and concentration. The time required for reading,
documentation and discussion of the high number of images vary substantially, and
15-60 minutes are needed, particularly if additional images, e.g. from follow-up
and/or multimodal diagnostic approaches with CT, PET or PET/CT have to be
evaluated. Furthermore, the imaging findings have comprehensively to be presented
in multidisciplinary conferences. The involved Radiologists are accordingly faced
with heavier workload, in particular when referring clinicians are getting more and
more aware of a comprehensive whole-body approach cutting down the total time
demand for imaging. Workflow optimization has to be considered as a prerequisite
for utilizing the potential of the whole-body imaging technology. Logistical
considerations should be aimed at minimizing the time demand for both, the patient
examination as well as the reading and reporting process. Challenging concepts for
redesigning the workflow of oncologic imaging are currently on the right track.
References:
1
Townsend DW. Dual-Modality Imaging: Combined anatomy and function. J
Nucl Med 2008; 49(6): 938-55.
2
Antoch G, Saoudi N, Kuehl H, Dahmen G, Mueller SP, Beyer T, Bockisch A,
Debatin JF, Freudenberg LS. Accuracy of whole-body dual-modality fluorine18-2-fluoro-2-deoxy-D-glucose positron emission tomography and computed
tomography (FDG-PET/CT) for tumor staging in solid tumors: comparison with
CT and PET. J Clin Oncol 2004; 22(21): 4357-68.
3
Maldonado A, González-Alenda FJ, Alonso M, Sierra JM. PET-CT in clinical
oncology. Clin Transl Oncol. 2007; 9(8): 494-505.
4
Schlemmer HP, Schäfer J, Pfannenberg C, Radny P, Korchidi S, MüllerHorvat C, Nägele T, Tomaschko K, Fenchel M, Claussen CD. Fast wholebody assessment of metastatic disease using a novel magnetic resonance
imaging system. Invest Radiol 2005; 40(2): 64-71.
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7
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9
Schroeder T, Ruehm SG, Debatin JF, Ladd ME, Barkhausen J, Goehde SC.
Detection of pulmonary nodules using a 2D HASTE MR sequence:
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HP, Severens JL, Adang EM, van der Kaa CH, Fütterer JJ, Barentsz J. MRI
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11
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