Review ArticleContinuing Education

Workflow and Scan Protocol Considerations for Integrated Whole-Body PET/MRI in Oncology

Axel Martinez-Möller, Matthias Eiber, Stephan G. Nekolla, Michael Souvatzoglou, Alexander Drzezga, Sibylle Ziegler, Ernst J. Rummeny, Markus Schwaiger and Ambros J. Beer
Journal of Nuclear Medicine September 2012, 53 (9) 1415-1426; DOI: https://doi.org/10.2967/jnumed.112.109348

Article Figures & Data

Figures

  • FIGURE 1.
    FIGURE 1.

    Diagram of basic acquisition protocol covering 2 bed positions in combined PET/MRI. For each PET bed position (4-min acquisition time in example), MRI AC sequence is acquired first and then MRI component can be used for further acquisitions without moving patient bed. BP1 = bed position 1; BP2 = bed position 2.

  • FIGURE 2.
    FIGURE 2.

    Diagram of acquisition protocol for combined PET/MRI focusing on single area of interest (in this example, liver imaging), with only limited MRI evaluation of partial or whole body. ax = axial; BP = bed position; cor = coronal; CM = contrast medium; DWI = diffusion-weighted imaging; Dyn. = dynamic; fs = fat-saturated.

  • FIGURE 3.
    FIGURE 3.

    Diagram of acquisition protocol focusing on head-and-neck imaging in combined PET/MRI with full diagnostic coverage of partial or whole body. ax = axial; BP = bed position; cor = coronal; CM = contrast medium; fs = fat-saturated.

  • FIGURE 4.
    FIGURE 4.

    Example of head-and-neck imaging in combined PET/MRI (18F-FDG): patient with cancer of oral cavity. (A–C) Coronal T1-weighted turbo spin echo, axial PET, and axial T2-weighted fat-saturated HASTE images show no distant metastases. (D and E) T2-weighted hyperintense lesion on MRI with high glucose metabolism on right side in frontal oral cavity is suggestive of tumor.

  • FIGURE 5.
    FIGURE 5.

    Diagram of acquisition protocol focusing on prostate imaging in combined PET/MRI with full diagnostic coverage of partial or whole body. ax = axial; BP = bed position; cor = coronal; CM = contrast medium; fs = fat-saturated.

  • FIGURE 6.
    FIGURE 6.

    Example of prostate imaging in combined PET/MRI (11C-choline): patient with radical prostatectomy and PSA recurrence. (A–C) Coronal T1-weighted turbo spin echo, axial PET, and axial T2-weighted fat-saturated HASTE images show no distant metastases. (D) Axial T2-weighted turbo spin echo image provides superb anatomic details of area of former prostate fossa. (E) Dynamic contrast-enhanced MR image shows early intense contrast enhancement in arterial phase. (F) In fused 11C-choline PET image, moderate focal high uptake is found in corresponding region. (G) Parametric map indicating area under curve confirms early and intense enhancement of suspected lesion.

  • FIGURE 7.
    FIGURE 7.

    Diagram of acquisition protocol focusing on liver imaging in combined PET/MRI with full diagnostic coverage of partial or whole body. ax = axial; BP = bed position; cor = coronal; CM = contrast medium; DWI = diffusion-weighted imaging; Dyn. = dynamic; fs = fat-saturated.

  • FIGURE 8.
    FIGURE 8.

    Example of liver imaging in combined PET/MRI (18F-FDG): patient with breast cancer and liver metastases. (A) Fused coronal T1-weighted turbo spin echo image with PET image shows hypermetabolic lesion in liver below medial part of diaphragm. (B and C) Axial PET image and axial fused image outline 2 adjacent liver metastases in right lobe. (D–G) Axial morphologic MR images (T2-weighted HASTE [D], diffusion-weighted [E], dynamic contrast-enhanced [F and G]) demonstrate high soft-tissue contrast on MRI and superb anatomic delineation of liver metastases.

  • FIGURE 9.
    FIGURE 9.

    Diagram of fully diagnostic whole-body acquisition protocol in combined PET/MRI. ax = axial; BP = bed position; cor = coronal; CM = contrast medium; DWI = diffusion-weighted imaging; Dyn. = dynamic; fs = fat-saturated; stir = short-τ inversion recovery.

  • FIGURE 10.
    FIGURE 10.

    Example of whole-body imaging in combined PET/MRI (68Ga-DOTATOC): patient with neuroendocrine cancer and liver metastases. (A) Fused coronal T2-weighted short-τ inversion recovery and PET images demonstrate whole extent of examination. Because of incomplete coverage of lower legs by total-imaging-matrix surface coils, intensity and quality of MRI images in this area are substantially reduced. (B and C) PET and fused images show multiple liver metastases with high somatostatin receptor expression. (D) Diffusion-weighted image (with b-value of 50 s/mm2) shows large metastasis with many surrounding small lesions. (E) In comparison to diffusion-weighted image, fused axial T2-weighted fat-saturated HASTE and PET image demonstrates that small lesions are not visible on PET. (F and G) Fused axial T2-weighted fluid-attenuated inversion recovery image and axial T1-weighted gadolinium-enhanced image show physiologic uptake of hypophysis and no evidence of brain metastases.

  • FIGURE 11.
    FIGURE 11.

    Patient with metallic implants from lumbar spine surgery. Metallic artifacts in CT image (A) result in region’s being incorrectly segmented as air in MRI-based attenuation map (B). Non-AC PET image (C) shows normal tracer distribution around implants, but MRI-based AC leads to large areas of underestimated uptake (D).

  • FIGURE 12.
    FIGURE 12.

    MRI-based attenuation map (top row) and corresponding 18F-FDG PET images (bottom row) acquired arms-down showing truncation in arms and resulting artifacts: inhomogeneity in liver (anterior–posterior gradient, yellow arrows) and sharp change in uptake in arms corresponding to limit of field of view (blue arrows).

  • FIGURE 13.
    FIGURE 13.

    Severe artifacts in 11C-choline PET images acquired arms-down. Truncation of attenuation map can occasionally lead to biased scatter correction, which renders complete regions unevaluable (yellow arrows).

Tables

  • TABLE 1

    Technical Aspects and Differences between PET and MRI Relevant for Optimizing Protocols in Integrated PET/MRI

    PETMRI
    Patient scheduleRigorous patient scheduleFlexible patient schedule
    Acquisition at fixed time after injectionAdditional imaging possible, depending on findings or motion
    High predictability of acquisition time
    Prescan preparationTracer administrationChecking of potential contraindications and renal insufficiency when gadolinium is used
    Resting of patient during uptake timeRemoval of all metal
    With 18F-FDG, previous fasting and glucose level measurement
    In-bed patient preparationVery fast; only uploading of patient onto tablePlacement of surface coils and headphones
    Radiation exposure for staff while near patientsTime-consuming (3–5 min)
    Field of view45–60 cm transaxially35–45 cm transaxially
    15–21 cm axiallyUp to 50 cm axially
    PlanningStraightforwardExperience for fine-tuning
    Defining of field of view and time per bed positionPlanning throughout scan
    Planning by operator at start, with no further interactionFrequent interaction with radiologist
    Often oblique plane acquisitions
    AcquisitionStep and shootIsocenter for optimal image quality
    Overlapping of bedsOccasional need for bed motion even in examination of single organs
    Respiratory motionProduction of blurringFrequent production of artifacts
    Possibility of respiratory gating; increase of acquisition time to preserve image qualityPossibility of breath-hold acquisition or respiratory gating
  • TABLE 2

    Technical Parameters for Different MRI Sequences

    RegionSequenceImage planeSlice thickness (mm)Gap (%)Slices (no.)Acquisition time (min:s)TR/TEMatrixField of view (mm)Resolution (mm2)GRAPPABreath holdRemarks
    AC
    Whole body3D T1 VIBE DixonCoronal3.1201280:193.60/1.23–2.46*192 × 1215004.1 × 2.62+MRI-based AC
    Diagnostic sequences for whole-body coverage
    Whole bodyT1 TSECoronal53025–361:11600/8.7384 × 2304502.0 × 1.22+ for chest, abdomen
    Whole bodyT2 STIRCoronal53025–361:25–3:15†7.9/500259 × 3844502.9 × 1.83Free breathing
    Diagnostic sequences for partial-body coverage
    Partial bodyT2 HASTE fat satAxial520251:081,600/95320 × 2603801.5 × 1.22Free breathingPartial body = chest to pelvis, dark-blood pulse
    Lungs3D VIBE + CMAxial40720:183.24/1.23320 × 2404001.7 × 1.32+11% slice oversampling
    Abdomen to pelvis3D VIBE + CMAxial50440:163.29/1.16320 × 2604601.8 × 1.42+Two stacks; 45% slice oversampling
    Prostate cancer recurrence
    ProstateT2 TSEAxial320314:474,610/101320 × 3102000.6 × 0.62–
    ProstateDWIAxial3.60205:394,500/93160 × 1202602.2 × 1.62–b = 50, 400, 800 s/mm2
    Prostate3D TWISTAxial3.60205:244.83/1.87192 × 1322602.0 × 1.42–DCE; temporal resolution, 4.25 s
    Primary staging of ENT tumors
    NeckT1 TSE ± CMAxial4.020303:461,330/10384 × 3842300.6 × 0.62–Each sequence before and after CM
    NeckT2 STIRAxial4.020303:485,810/54320 × 3202300.7 × 0.72–
    NeckT1 TSE fat sat + CMCoronal4.020203:371,290/9.6320 × 3202300.7 × 0.72–
    NeckT2 STIRSagittal4.02284:115,090/57384 × 3452400.7 × 0.62–
    Focus on potential liver metastases
    LiverT2 HASTECoronal5.020300:421,400/96256 × 2563801.5 × 1.53+
    LiverT2 HASTE fat satAxial5.020351:081,600/95320 × 2603801.5 × 1.22+
    LiverDWIAxial5.020355:047,800/82192 × 1443802.6 × 2.02Free breathingb = 50, 400, 800 s/mm2
    LiverVIBEAxial3.020640:184.06/1.91320 × 2403801.6 × 1.22+DCE: without CM, arterial, portal-venous, late phase; 13% slice oversampling
    Diagnostic whole-body protocol‡
    BrainT2 FLAIRAxial4.030252:089,000/85256 × 1922201.1 × 0.92–
    BrainT1 GRE +CMAxial4.030252:10250/2.48320 × 2562200.9 × 0.7—–
    BrainT1 GRE +CMCoronal4.030351:25250/2.48320 × 2562200.9 × 0.7—–
    LungsT2 HASTECoronal8.030300:22650/28320 × 2564001.6 × 1.33+
    LiverDWIAxial5.020354:089,200/85192 × 1443802.6 × 2.02Free breathingb = 50, 800 s/mm2
    NeckVIBE DixonAxial4.020360:285.61/2.46–3.69320 × 2604001.5 × 1.32–44% slice oversampling

    • ↵* Fat saturation techniques with Dixon require 2 repetition times.

    • ↵† Acquisition time is dependent on number of averages and slices per slab specific for different body regions (3–5).

    • ↵‡ Only sequences not part of other protocols are mentioned.

    • 3D = 3-dimensional; b = b-value; BLADE = noncartesian k-space data acquisition for motion correction in TSE sequences; CM = contrast medium; DCE = dynamic contrast enhanced; DWI = diffusion-weighted imaging; FLAIR = fluid-attenuated inversion recovery; GRAPPA = generalized autocalibrating partially-parallel acquisition (as integrated parallel-acquisition technique [iPAT; Siemens Healthcare]); GRE = gradient echo; sat = saturation; STIR = short-τ inversion recovery; TE = echo time; TR = repetition time; TSE = turbo spin echo; TWIST = dynamic contrast-enhanced sequence with k-space sharing.

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