Patient description: The patient is a 16-year-old girl recently diagnosed with myasthenia gravis, class IIa. She complains of diplopia and weakness affecting in her upper extremities. She had a positive anti-AChR antibody test, and her single fiber electromyography (SFEMG) was positive. She is on acetylcholinesterase inhibitor treatment combined with immunosuppressants. But she still has some symptoms. She does not smoke or use illicit drugs. She is not sexually active, and her menses are regular. Her physical exam and lab studies are not remarkable for any other abnormalities. BP: 110/75 Hgb: 11 g/dl WBC: 8000 /mm3 Plt: 300000 /ml Creatinine: 0.5 mg/dl BUN: 10 mg/dl Beta hcg: negative for pregnancy

Clinical trial eligibility criteria: eligible ages (years): 0.0-30.0,  Relapsed Pediatric Solid Tumors Refractory Pediatric Solid Tumors Rhabdomyosarcoma Ewing Sarcoma Osteosarcoma Neuroblastoma Wilms Tumor Hepatic Tumor Germ Cell Tumor Desmoid Tumor AGE: ≤ 30 years of age. Histologically confirmed malignant solid tumors, which may but are not limited to rhabdomyosarcoma and other soft tissue sarcomas, Ewing's sarcoma family of tumors, osteosarcoma, neuroblastoma, Wilms' tumor, hepatic tumors, germ cell tumors, and desmoid tumors. TUMOR Target lesion(s) must be located in bone or soft tissue in close proximity to bone. Target lesions must be reachable within the normal safety margins of HIFU as specified in the instructions for use. Radiographically evaluable or measurable solid tumor target lesion(s). Malignant Tumor: The patient's cancer must have relapsed after or failed to respond to frontline curative therapy and there must not be other potentially curative treatment options available. Curative therapy may surgery, radiation therapy, chemotherapy, or any combination of these modalities. PRIOR Patients must have fully recovered from the acute toxic effects of all prior chemotherapy, immunotherapy, or radiotherapy prior to entering on this study. No limitation on the number of prior chemotherapy regimens that the patient may have received prior to study entry. Myelosuppressive chemotherapy: The last dose of all myelosuppressive anticancer drugs must be at least 3 weeks prior to study entry. Immunotherapy: The last dose of immunotherapy (monoclonal antibody or vaccine) must be at least 4 weeks prior to study entry. Biologic (anti-cancer agent): The last dose of all biologic agents for the treatment of the patient's cancer (such as retinoids or tyrosine kinase inhibitors) must be at least 7 days prior to study entry. Radiation therapy: The last dose of radiation to more than 25 % of marrow containing bones (pelvis, spine, skull) must be at least 4 weeks prior to study entry. The last dose of all other local palliative (limited port) radiation must be at least 2 weeks prior to study entry. Stem Cell Transplantation. At least 2 months post-autologous stem cell transplant or at least 3 months post-allogeneic transplant and recovered from toxicities without evidence of graft versus host disease and on stable doses of immunosuppressive medications if required. Growth Factors. The last dose of colony stimulating factors, such as filgrastim, sargramostim, and erythropoietin, must be at least 1 week prior to study entry, the last dose of long-acting colony stimulating factors, such as pegfilgrastim, must be at least 2 weeks prior to study entry. No other anti-cancer therapy (chemotherapy, biological therapy, radiation therapy) is permitted during HIFU treatment and post treatment follow up for tolerability (see section 3.3). Patients > 16 years old must have a Karnofsky performance level ≥ 50%, and children ≤ 16 years old must have a Lansky performance level ≥ 50% (See Appendix I). Patients who are unable to walk because of paralysis or motor weakness, but who are up in a wheelchair will be considered ambulatory for the purpose of calculating the performance score Peripheral absolute neutrophil count (ANC) of ≥750/µL 2. Platelet count ≥75,000/µL (may receive transfusions) RENAL Age-adjusted normal serum creatinine OR a creatinine clearance ≥60 mL/min/1.73 m2 Defined as no dyspnea at rest, and a pulse oximetry >94% on room air if there is clinical indication for determination Normal PT, PTT and INR < 1.5 x ULN (including patients on prophylactic anticoagulation)  Clinically significant unrelated systemic illness, such as serious infections, hepatic, renal or other organ dysfunction, which in the judgment of the Principal or Associate Investigator would compromise the patient's ability to tolerate the general anesthetic required for the procedure. Implant or prosthesis or scar tissue within the path of the HIFU beam. Target <1 cm from nerve plexus, spinal canal, bladder, bowel Target in contact with hollow viscera Lesion in the skull Inability to undergo MRI and/or contraindication for MRI Inability to tolerate stationary position during HIFU Patients currently receiving other anticancer agents. Patients currently receiving other investigational agents