Here's the pertinent portion of the federal regulation as it pertains to Invivo's application:
Sec. 814.102 Designation of HUD status.
(a)Request for designation. Prior to submitting an HDE application, the applicant shall submit a request for HUD designation to FDA's Office of Orphan Products Development. The request shall contain the following:
(1) A statement that the applicant requests HUD designation for a rare disease or condition or a valid subset of a disease or condition which shall be identified with specificity;
(2) The name and address of the applicant, the name of the applicant's primary contact person and/or resident agent, including title, address, and telephone number;
(3) A description of the rare disease or condition for which the device is to be used, the proposed indication or indications for use of the device, and the reasons why such therapy is needed. If the device is proposed for an indication that represents a subset of a common disease or condition, a demonstration that the subset is medically plausible should be included;
(4) A description of the device and a discussion of the scientific rationale for the use of the device for the rare disease or condition; and
(5) Documentation, with appended authoritative references, to demonstrate that the device is designed to treat or diagnose a disease or condition that affects or is manifested in fewer than 4,000 people in the United States per year. If the device is for diagnostic purposes, the documentation must demonstrate that fewer than 4,000 patients per year would be subjected to diagnosis by the device in the United States. Authoritative references include literature citations in specialized medical journals, textbooks, specialized medical society proceedings, or governmental statistics publications. When no such studies or literature citations exist, the applicant may be able to demonstrate the prevalence of the disease or condition in the United States by providing credible conclusions from appropriate research or surveys.
(b)FDA action. Within 45 days of receipt of a request for HUD designation, FDA will take one of the following actions:
(1) Approve the request and notify the applicant that the device has been designated as a HUD based on the information submitted;
(2) Return the request to the applicant pending further review upon submission of additional information. This action will ensue if the request is incomplete because it does not on its face contain all of the information required under 814.102(a). Upon receipt of this additional information, the review period may be extended up to 45 days; or
(3) Disapprove the request for HUD designation based on a substantive review of the information submitted. FDA may disapprove a request for HUD designation if:
(i) There is insufficient evidence to support the estimate that the disease or condition for which the device is designed to treat or diagnose affects or is manifested in fewer than 4,000 people in the United States per year;
(ii) FDA determines that, for a diagnostic device, 4,000 or more patients in the United States would be subjected to diagnosis using the device per year; or
(iii) FDA determines that the patient population defined in the request is not a medically plausible subset of a larger population.
(c)Revocation of designation. FDA may revoke a HUD designation if the agency finds that:
(1) The request for designation contained an untrue statement of material fact or omitted material information; or
(2) Based on the evidence available, the device is not eligible for HUD designation.
(d)Submission. The applicant shall submit two copies of a completed, dated, and signed request for HUD designation to: Office of Orphan Products Development (HF-35), Food and Drug Administration, 5600 Fishers Lane, Rockville, MD 20857.
If the FDA follows regulation, then there should be SOME response back.